06 9701 41 3RP - Weebly · 2018-09-09 · Reacting 100 g of alloy in this way produced 8.0 dm3 of...

READ THESE INSTRUCTIONS FIRST

Write your Centre number, candidate number and name on all the work you hand in.Write in dark blue or black pen.You may use a soft pencil for any diagrams, graphs or rough working.Do not use staples, paper clips, highlighters, glue or correction fl uid.DO NOT WRITE IN ANY BARCODES.

Section AAnswer all questions.

Section BAnswer all questions.

You may lose marks if you do not show your working or if you do not useappropriate units.A Data Booklet is provided.Electronic calculators may be used.

At the end of the examination, fasten all your work securely together.The number of marks is given in brackets [ ] at the end of each question or part question.

CHEMISTRY 9701/41

Paper 4 Structured Questions May/June 2013

2 hours

Candidates answer on the Question Paper.

Additional Materials: Data Booklet

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONSGeneral Certifi cate of Education Advanced Level

This document consists of 15 printed pages and 1 blank page.

[Turn overIB13 06_9701_41/3RP© UCLES 2013

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Section A

Answer all the questions in the spaces provided.

1 (a) What is meant by the term standard electrode potential, SEP?

...........................................................................................................................................

...........................................................................................................................................[2]

(b) Draw a fully labelled diagram of the apparatus you could use to measure the SEP of the Fe3+

/ Fe2+ electrode.

[5]

(c) The reaction between Fe3+ ions and I– ions is an equilibrium reaction.

2Fe3+(aq) + 2I–(aq) 2Fe2+(aq) + I2(aq)

(i) Use the Data Booklet to calculate the for this reaction.

....................................................................................................................................

(ii) Hence state, with a reason, whether there will be more products or more reactants at equilibrium.

....................................................................................................................................

....................................................................................................................................

(iii) Write the expression for Kc for this reaction, and state its units.

Kc =

units .................................................

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ForExaminer’s

Use An experiment was carried out using solutions of Fe3+(aq) and I–(aq) of equal

concentrations. 100 cm3 of each solution were mixed together, and allowed to reach equilibrium.

The concentrations at equilibrium of Fe3+(aq) and I2(aq) were as follows.

[Fe3+(aq)] = 2.0 × 10–4 mol dm–3

[I2(aq)] = 1.0 × 10–2 mol dm–3

(iv) Use these data, together with the equation given in (c), to calculate the concentrations of Fe2+(aq) and I–(aq) at equilibrium.

[Fe2+(aq)] = ............................... mol dm–3

[I–(aq)] = ............................... mol dm–3

(v) Calculate the Kc for this reaction.

Kc = ......................................................[8]

[Total: 15]

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2 Ethyl ethanoate is hydrolysed slowly by water in the following acid-catalysed reaction.

H+

CH3CO2CH2CH3 + H2O CH3CO2H + CH3CH2OH

The concentration of ethyl ethanoate was determined at regular time intervals as the reaction progressed.

Two separate experiments were carried out, with different HCl concentrations. The following graph shows the results of an experiment using [HCl ] = 0.1 mol dm–3.

0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0 20 40 60 80 100 120

time / min

[CH3CO2CH2CH3]/ mol dm–3

(a) When the experiment was carried out using [HCl ] = 0.2 mol dm–3, the following results were obtained.

time / min [CH3CO2CH2CH3]/ mol dm–3

0 0.200

10 0.160

25 0.115

50 0.067

75 0.038

100 0.022

125 0.013

(i) Plot these data on the axes above, and draw a line of best fi t.

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(ii) Use one of the graphs to show that the reaction is fi rst order with respect to CH3CO2CH2CH3.

Show all your working, and show clearly any construction lines you draw on the graphs.

(iii) Use the graphs to calculate the order of reaction with respect to HCl.


(iv) Write the rate equation for this reaction, and calculate the value of the rate constant.

rate =

[7]

(b) (i) Why is it not possible to determine the order of reaction with respect to water in this experiment?

....................................................................................................................................

....................................................................................................................................

(ii) Although [CH3CO2CH2CH3] decreases during each experiment, [HCl ] remains the same as its initial value.

Why is this?

....................................................................................................................................

....................................................................................................................................[2]

[Total: 9]

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3 (a) (i) What is meant by the density of a substance?

....................................................................................................................................

(ii) Use data from the Data Booklet to explain why the density of iron is greater than that of calcium.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[3]

(b) In general, reactions of the compounds of transition elements can be classifi ed under one or more of the following headings.

acid-base ligand exchange precipitation redox

Choose the most suitable heading to describe each of the following reactions, by placing a tick ( ) in the appropriate column in the table below.

Only one tick should be placed against each reaction.

reaction acid-base ligandexchange precipitation redox

[Cu(H2O)6]2+ + 4NH3 → [Cu(NH3)4]2+ + 6H2O

[Cu(H2O)6]2+ + 4HCl → [CuCl 4]2– + 4H+ + 6H2O

2FeCl 2 + Cl 2 → 2FeCl 3

[Fe(H2O)6]2+ + 2OH– → Fe(OH)2 + 6H2O

2Fe(OH)2 + ½O2 + H2O → 2Fe(OH)3

CrO3 + 2HCl → CrO2Cl 2 + H2O

Cr(H2O)3(OH)3 + OH– → [Cr(H2O)2(OH)4]– + H2O

[Cr(OH)4]– + 1½H2O2 + OH– → CrO42– + 4H2O

[8]

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(c) Alloys of aluminium, titanium and vanadium are used in aerospace and marine equipment, and in medicine.

When a powdered sample of one such alloy is heated with an excess of aqueous NaOH, only the aluminium reacts, according to the following equation.

2Al (s) + 2OH–(aq) + 6H2O(l) → 2[Al (OH)4]–(aq) + 3H2(g)

Reacting 100 g of alloy in this way produced 8.0 dm3 of hydrogen, measured under room conditions.

Calculate the percentage by mass of aluminium in the alloy.

percentage = ........................ %[3]

[Total: 14]

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4 Because of the lack of reactivity of the nitrogen molecule, extreme conditions need to be used to synthesise ammonia from nitrogen in the Haber process.

(a) Suggest an explanation for the lack of reactivity of the nitrogen molecule, N2.

...........................................................................................................................................

...........................................................................................................................................[1]

(b) Under conditions of high temperature, nitrogen and oxygen react together to give oxides of nitrogen.

(i) Write an equation for a possible reaction between nitrogen and oxygen.

....................................................................................................................................

(ii) State two situations, one natural and one as a result of human activities, in which nitrogen and oxygen react together.

....................................................................................................................................

....................................................................................................................................

(iii) What is the main environmental effect of the presence of nitrogen oxides in the atmosphere?

....................................................................................................................................[4]

(c) Describe and explain how the basicities of ethylamine and phenylamine compare to that of ammonia.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[4]

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(d) Compound X is a useful intermediate in the synthesis of pharmaceuticals. X can be synthesised from chloromethylbenzene according to the following scheme.

T W

step 1

step 3 step 4

step 5

X

CH2Cl step 2CH2CN

CH2CH2NH CH2

CH2CO2H

O

C

(i) What type of reaction is each of the following?

step 1 .........................................................................................................................

step 2 .........................................................................................................................

(ii) Suggest reagents and conditions for

step 1, ........................................................................................................................

step 2. ........................................................................................................................

(iii) Draw the structures of the intermediates T and W in the boxes above.[6]

[Total: 15]

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5 (a) A series of experiments is carried out in which the reagent shown at the top of the column of the table is mixed, in turn, with each of the reagents at the side.

Complete the following table by writing in each box the formula of any gas produced. Write x in the box if no gas is produced. The fi rst column has been completed as an illustration.

H2O

OH CO2H OH

Na H2

KOH(aq) x

Na2CO3(aq) x

[5]

(b) Compound C is responsible for the pleasant aroma of apples. It can be prepared from phenol by the following 3-step synthesis.

OH OH

C

A

CH3H3CCH3

step1

OH

C

B

CH3H3CCH3

step2

O

O

C

C

CH3

CH3

H3CCH3

step3

(i) The only by-product of step 1 is HCl. Suggest the reagent that was used to react with phenol to produce compound A.

....................................................................................................................................

(ii) What type of reaction is occurring in step 2?

....................................................................................................................................

(iii) What reagents and conditions are required for step 3?

....................................................................................................................................

(iv) State the reagent and conditions needed to convert C back to B, the reverse ofstep 3.

....................................................................................................................................[5]

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(c) (i) Either compound A or compound B, or both, react with the following reagents. For each reagent draw the structure of the organic product formed with A, and with

B. If no reaction occurs, write ‘no reaction’ in the relevant box.

reagent and conditions product with A product with B

an excess of Br2(aq)

heat with HBr

pass vapour overheated Al 2O3

heat with acidifi ed K2Cr2O7

(ii) Choose one of the above reactions to enable you to distinguish between A and B.

State below the observations you would make with each compound.

reagent observation with A observation with B

[7]

[Total: 17]

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Section B


6 There are two important polymerisations that occur within living organisms – protein synthesis and the formation of DNA.

(a) Complete the table placing a tick ( ) in the correct column to indicate in which process each substance could be used.

substance protein synthesis formation of DNA

adenine

alanine

aspartate

phosphate[3]

(b) Proteins and DNA form different helical structures. Briefl y describe the bonding that maintains the shape of each of these helical structures.

protein ...............................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

DNA ..................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[4]

(c) Describe the differences in bonding in the primary and tertiary structures of proteins. Your answer should include reference both to the nature of the bonding and the types of amino acid causing it.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[3]

[Total: 10]

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7 Modern methods of analysis have had far-reaching effects on a number of branches of science including medicine, forensic science, environmental monitoring and archaeology.

(a) Outline, in simple terms, the technique of DNA fi ngerprinting.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[4]

(b) Complete the table by indicating whether the items can be used for DNA fi ngerprinting. Use a tick ( ) for items which can be used for DNA fi ngerprinting and a cross (x) for items

which cannot.

item for testing suitable for DNA fi ngerprinting

human hair

piece of a fl int tool

piece of Iron Age pot

piece of Roman leather

[3]

(c) Various forms of chromatography can be used to separate and analyse mixtures.HPLC (high performance liquid chromatography) can be used to separate each of the following mixtures. State another method of chromatography which would separate each mixture.

insecticides in a sample of water ......................................................................................

dyes present in a foodstuff ...............................................................................................

drug residue in an athlete’s urine .....................................................................................[3]

[Total: 10]

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8 In recent years there has been a lot of interest in polymers in the form of gels that absorb aqueous materials. One of the largest uses of these polymers is in disposable nappies (diapers). The gel which is used in this case is a polymer of propenoic acid.

O

OH

propenoic acid

(a) (i) Draw a section of the polymer of propenoic acid showing two repeat units.

(ii) By what type of chemical reaction is this polymer formed?

....................................................................................................................................

(iii) By what type of bonding is water held on the polymer?

....................................................................................................................................[3]

(b) For some disposable nappies (diapers), the monomer is a mixture of propenoic acid and sodium propenoate. The properties of the polymer are infl uenced by the proportion of sodium salt in the monomer mixture.

(i) Suggest and explain how the difference in the structure of this polymer compared to one formed only from propenoic acid might affect the water absorbing properties of the polymer.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

(ii) Suggest a property the polymer should have in order to be used in disposable products.

....................................................................................................................................[3]

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(c) A variation on the gel used for disposable nappies (diapers) containing more sodium propenoate has been used to treat soils contaminated by heavy metals such as lead (Pb2+) and cadmium (Cd2+). Suggest why the gel is effective.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[2]

(d) Another variation on this type of polymer is used in hair gels. In these, the polymer chains are cross-linked by a compound known as pentaerythritol.

OH

OH

HO

HO

pentaerythritol

(i) By what type of chemical reaction are the cross-links in this polymer formed?

....................................................................................................................................

(ii) It is important that the gel should be easily washed out of hair. What is it about the structure of the polymer that allows this to happen?

....................................................................................................................................[2]

[Total: 10]

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9701/41/M/J/13© UCLES 2013

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Section A


1 A bromoalkane, R–Br, is hydrolysed by aqueous sodium hydroxide.

(a) (i) Write a balanced equation for this reaction.

....................................................................................................................................

(ii) What type of reaction is this?

....................................................................................................................................[2]

(b) The concentration of bromoalkane was determined at regular time intervals as the reaction progressed.

Two separate experiments were carried out, with different NaOH concentrations. The graph below shows the results of an experiment using [NaOH] = 0.10 mol dm–3.

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.010

0 50 100 150 200 250

time / min

[R–Br]/ mol dm–3

When the experiment was repeated using [NaOH] = 0.15 mol dm–3, the following results were obtained.

time / min [R–Br] / mol dm–3

0 0.010040 0.007080 0.0049

120 0.0034160 0.0024200 0.0017240 0.0012


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(ii) Use one of the graphs to confi rm that the reaction is fi rst order with respect to R–Br. Show all your working, and show clearly any construction lines you draw.

(iii) Use the graphs to calculate the order of reaction with respect to NaOH. Show all your working, and show clearly any construction lines you draw on the graphs.


rate =

[7]

(c) Nitric oxide, NO, and bromine vapour react together according to the following equation.

2NO(g) + Br2(g) → 2NOBr(g) ∆H = –23 kJ mol–1

The reaction has an activation energy of +5.4 kJ mol–1 .

Use the following axes to sketch a fully-labelled reaction pathway diagram for this reaction.

Include all numerical data on your diagram.

energy/ kJ mol–1

2NO + Br2

extent of the reaction[2]

[Total: 11]

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2 (a) (i) With the aid of a fully-labelled diagram, describe the standard hydrogen electrode.

(ii) Use the Data Booklet to calculate the standard cell potential for the reaction between Cr2+ ions and Cr2O7

2– ions in acid solution, and construct a balanced equation for the reaction.

= ......................... V

equation .....................................................................................................................

(iii) Describe what you would see if a blue solution of Cr2+ ions was added to an acidifi ed solution of Cr2O7

2– ions until reaction was complete.

....................................................................................................................................

....................................................................................................................................[8]

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(b) A buffer solution is to be made using 1.00 mol dm–3 ethanoic acid, CH3CO2H, and 1.00 mol dm–3 sodium ethanoate, CH3CO2Na.

Calculate to the nearest 1 cm3 the volumes of each solution that would be required to make 100 cm3 of a buffer solution with pH 5.50.

Clearly show all steps in your working. Ka (CH3CO2H) = 1.79 × 10–5

mol dm–3

volume of 1.00 mol dm–3 CH3CO2H = ......................... cm3

volume of 1.00 mol dm–3 CH3CO2Na = ......................... cm3

[4]

(c) Write an equation to show the reaction of this buffer solution with each of the following.

(i) added HCl .................................................................................................................

(ii) added NaOH ..............................................................................................................[2]

(d) Choose one reaction in organic chemistry that is catalysed by an acid, and write the structural formulae of the reactants and products in the boxes below.

H+

[3]

[Total: 17]

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3 (a) Describe the reagents and conditions required to form a nitro compound from the following.

CH3

methylbenzene .......................................................(i)

OH

phenol .......................................................(ii)

[3]

(b) Draw the structure of the intermediate organic ion formed during the nitration of benzene.

[1]

(c) In the box over the arrow below, write the reagents needed to convert nitrobenzene into phenylamine.

NO2 NH2

[1]

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(d) Phenylamine can be converted into the organic compounds A and B.

(i) Suggest the structural formulae of A and B in the boxes below.

(ii) Suggest suitable reagents and conditions for step 1, and write them in the box over the arrow.

step 1

NH2 N+

O– Na+

Cl –N

Br2(aq)

BA

[3]

(e) When phenylamine is treated with propanoyl chloride a white crystalline compound, C, C9H11NO, is formed.

(i) Name the functional group formed in this reaction. ...................................................

(ii) Calculate the percentage by mass of nitrogen in C.

percentage = ........................ %

(iii) Draw the structural formula of C.

[3]

[Total: 11]

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4 (a) (i) Suggest why transition elements show variable oxidation states in their compounds whereas s-block elements like calcium do not.

....................................................................................................................................

....................................................................................................................................

(ii) Calculate the oxidation number of the metal in each of the following ions.

VO2+ .......................................

CrF62– .......................................

MnO42– .......................................

[4]

(b) Explain why transition element complexes are often coloured whereas compounds of s-block elements such as calcium and sodium are not.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[4]

(c) SO2 and MnO4– react together in acidic solution.

(i) Use the Data Booklet to construct a balanced equation for this reaction.

....................................................................................................................................

(ii) Describe the colour change you would see when SO2(aq) is added to a sample of acidifi ed KMnO4 until the SO2 is in excess.

from ............................................................ to ........................................................[3]

(d) Describe the observations you would make when NH3(aq) is added gradually to a solution containing Cu2+ ions, until the NH3 is in an excess.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[3]

[Total: 14]

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5 Coffee beans contain chlorogenic acid.

OO

O

HOHO

OH

OH

chlorogenic acid

OH

OH

(a) (i) Draw circles around any chiral centres in the above structure.

(ii) Write down the molecular formula of chlorogenic acid.

....................................................................................................................................

(iii) How many moles of H2(g) will be evolved when 1 mol of chlorogenic acid reacts with an excess of sodium metal?

....................................................................................................................................

(iv) How many moles of NaOH(aq) will react with 1 mol of chlorogenic acid under each of the following conditions?

in the cold ...............................................

on heating ...............................................[6]

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(b) On heating with dilute aqueous acid, chlorogenic acid produces two compounds, D and E.

chlorogenic aciddil. H+(aq)

heat

O

HOHO

HOOH

+

OH

OH

D E

O OH

OH

conc.H2SO4heat

F G

C7H6O3

Br2(aq)in excess

(i) What type of reaction is chlorogenic acid undergoing when D and E are formed?

....................................................................................................................................

When compound D is heated with concentrated H2SO4, compound F, C7H6O3, is formed.

Compound F evolves CO2(g) when treated with Na2CO3(aq), and decolourises Br2(aq), giving a white precipitate. It does not, however, decolourise cold dilute acidifi ed KMnO4.

When compound E is treated with an excess of Br2(aq), compound G is produced.

(ii) If the test with cold dilute acidifi ed KMnO4 had been positive, which functional group would this have shown to be present in F?

....................................................................................................................................

(iii) Name the functional groups in compound F that would react with the following.

Na2CO3(aq) ................................................. Br2(aq) .................................................

(iv) Suggest structures for compounds F and G and draw them in the relevant boxes above.

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(v) Compound E is one of a pair of stereoisomers.

What type of stereoisomerism is shown by compound E?

....................................................................................................................................

(vi) Draw the structure of the other stereoisomer in the box below.

[8]

(c) Calculate the volume of 0.1 mol dm–3 NaOH that is needed to react completely with 0.1 g of compound E.

volume = ....................... cm3

[3]

[Total: 17]

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Section B



(a) Complete the table by placing a tick ( ) in the correct column to indicate in which process each substance could be used.


cysteine

cytosine

glutamine

guanine[3]

(b) DNA consists of a double helical structure.

(i) Describe the bonding between the two strands in DNA and state which part of each strand is joined by it.

....................................................................................................................................

....................................................................................................................................

(ii) How does the strength of this bonding relate to the mechanism of the replication of DNA?

....................................................................................................................................

....................................................................................................................................[4]

(c) Some diseases are caused by changes in the structure of proteins. Explain the genetic basis of these changes.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[3]

[Total: 10]

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7 The techniques of mass spectrometry and NMR spectroscopy are useful in determining the structures of organic compounds.

(a) The three peaks of highest mass in the mass spectrum of organic compound Lcorrespond to masses of 142, 143 and 144.

The ratio of the heights of the M : M+1 peaks is 43.3 : 3.35, and the ratio of heights ofthe M : M+2 peaks is 43.3 : 14.1.

(i) Use the data to calculate the number of carbon atoms present in L.

(ii) Explain what element is indicated by the M+2 peak.

....................................................................................................................................

....................................................................................................................................

Compound L reacts with sodium metal. The NMR spectrum of compound L is given below.

9 8 7 6 5 4 3 2 1 0δ / ppm

4

2

1

(iii) What does the NMR spectrum tell you about the number of protons in L and their chemical environments?

....................................................................................................................................

....................................................................................................................................

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(iv) Use the information given and your answers to (i), (ii) and (iii) to deduce a structure for L.

Explain how you arrive at your answer.

structure of L

[7]

(b) The molecular formula C3H6 represents the compounds propene and cyclopropane.

CH3CH CH2

propene cyclopropane

C

H

HC

H

H

C

H

H

(i) Suggest one difference in the fragmentation patterns of the mass spectra of these compounds.

....................................................................................................................................

....................................................................................................................................

(ii) Suggest two differences in the NMR spectra of these compounds.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[3]

[Total: 10]

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8 In recent years there has been considerable interest in a range of polymers known as ‘hydrogels’. These polymers are hydrophilic and can absorb large quantities of water.

(a) The diagram shows part of the structure of a hydrogel.

C

OO

CH

O O

CH2

CH2

CH

C

OOC

CCH2

C

HO

CH2CH2

CH2 OH

CH2

CH CH

OO

CH2

The hydrogel is formed from chains of one polymer which are cross-linked using another molecule.

(i) Draw the structure of the monomer used in the polymer chains.

(ii) State the type of polymerisation used to form these chains.

....................................................................................................................................

....................................................................................................................................

(iii) Draw the structure of the molecule used to cross-link the polymer chains.

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(iv) During the cross-linking, a small molecule is formed as a by-product. Identify this molecule.

....................................................................................................................................[5]

(b) Once a hydrogel has absorbed water, it can be dried and re-used many times. Explain why this is possible, referring to the structure on the opposite page.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[2]

(c) Not every available side chain in the polymer is cross-linked, and the amount ofcross-linking affects the properties of the hydrogel.

(i) The amount of cross-linking has little effect on the ability of the gel to absorb water. Suggest why this is the case.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

(ii) Suggest one property of the hydrogel that will change if more cross-linking takes place. Explain how the increased cross-linking brings about this change.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[3]

[Total: 10]

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CHEMISTRY 9701/43


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This document consists of 15 printed pages and 1 blank page.

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Section A


1 (a) What is meant by the term standard electrode potential, SEP?

...........................................................................................................................................

...........................................................................................................................................[2]

(b) Draw a fully labelled diagram of the apparatus you could use to measure the SEP of the Fe3+

/ Fe2+ electrode.

[5]

(c) The reaction between Fe3+ ions and I– ions is an equilibrium reaction.

2Fe3+(aq) + 2I–(aq) 2Fe2+(aq) + I2(aq)

(i) Use the Data Booklet to calculate the for this reaction.

....................................................................................................................................

(ii) Hence state, with a reason, whether there will be more products or more reactants at equilibrium.

....................................................................................................................................

....................................................................................................................................

(iii) Write the expression for Kc for this reaction, and state its units.

Kc =

units .................................................

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Use An experiment was carried out using solutions of Fe3+(aq) and I–(aq) of equal

concentrations. 100 cm3 of each solution were mixed together, and allowed to reach equilibrium.

The concentrations at equilibrium of Fe3+(aq) and I2(aq) were as follows.

[Fe3+(aq)] = 2.0 × 10–4 mol dm–3

[I2(aq)] = 1.0 × 10–2 mol dm–3

(iv) Use these data, together with the equation given in (c), to calculate the concentrations of Fe2+(aq) and I–(aq) at equilibrium.

[Fe2+(aq)] = ............................... mol dm–3

[I–(aq)] = ............................... mol dm–3

(v) Calculate the Kc for this reaction.

Kc = ......................................................[8]

[Total: 15]

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2 Ethyl ethanoate is hydrolysed slowly by water in the following acid-catalysed reaction.

H+

CH3CO2CH2CH3 + H2O CH3CO2H + CH3CH2OH

The concentration of ethyl ethanoate was determined at regular time intervals as the reaction progressed.

Two separate experiments were carried out, with different HCl concentrations. The following graph shows the results of an experiment using [HCl ] = 0.1 mol dm–3.

0

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0 20 40 60 80 100 120

time / min

[CH3CO2CH2CH3]/ mol dm–3

(a) When the experiment was carried out using [HCl ] = 0.2 mol dm–3, the following results were obtained.

time / min [CH3CO2CH2CH3]/ mol dm–3

0 0.200

10 0.160

25 0.115

50 0.067

75 0.038

100 0.022

125 0.013


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(ii) Use one of the graphs to show that the reaction is fi rst order with respect to CH3CO2CH2CH3.


(iii) Use the graphs to calculate the order of reaction with respect to HCl.



rate =

[7]

(b) (i) Why is it not possible to determine the order of reaction with respect to water in this experiment?

....................................................................................................................................

....................................................................................................................................

(ii) Although [CH3CO2CH2CH3] decreases during each experiment, [HCl ] remains the same as its initial value.

Why is this?

....................................................................................................................................

....................................................................................................................................[2]

[Total: 9]

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3 (a) (i) What is meant by the density of a substance?

....................................................................................................................................

(ii) Use data from the Data Booklet to explain why the density of iron is greater than that of calcium.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[3]

(b) In general, reactions of the compounds of transition elements can be classifi ed under one or more of the following headings.

acid-base ligand exchange precipitation redox

Choose the most suitable heading to describe each of the following reactions, by placing a tick ( ) in the appropriate column in the table below.

Only one tick should be placed against each reaction.

reaction acid-base ligandexchange precipitation redox

[Cu(H2O)6]2+ + 4NH3 → [Cu(NH3)4]2+ + 6H2O

[Cu(H2O)6]2+ + 4HCl → [CuCl 4]2– + 4H+ + 6H2O

2FeCl 2 + Cl 2 → 2FeCl 3

[Fe(H2O)6]2+ + 2OH– → Fe(OH)2 + 6H2O

2Fe(OH)2 + ½O2 + H2O → 2Fe(OH)3

CrO3 + 2HCl → CrO2Cl 2 + H2O

Cr(H2O)3(OH)3 + OH– → [Cr(H2O)2(OH)4]– + H2O

[Cr(OH)4]– + 1½H2O2 + OH– → CrO42– + 4H2O

[8]

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(c) Alloys of aluminium, titanium and vanadium are used in aerospace and marine equipment, and in medicine.

When a powdered sample of one such alloy is heated with an excess of aqueous NaOH, only the aluminium reacts, according to the following equation.

2Al (s) + 2OH–(aq) + 6H2O(l) → 2[Al (OH)4]–(aq) + 3H2(g)

Reacting 100 g of alloy in this way produced 8.0 dm3 of hydrogen, measured under room conditions.

Calculate the percentage by mass of aluminium in the alloy.

percentage = ........................ %[3]

[Total: 14]

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4 Because of the lack of reactivity of the nitrogen molecule, extreme conditions need to be used to synthesise ammonia from nitrogen in the Haber process.

(a) Suggest an explanation for the lack of reactivity of the nitrogen molecule, N2.

...........................................................................................................................................

...........................................................................................................................................[1]

(b) Under conditions of high temperature, nitrogen and oxygen react together to give oxides of nitrogen.

(i) Write an equation for a possible reaction between nitrogen and oxygen.

....................................................................................................................................

(ii) State two situations, one natural and one as a result of human activities, in which nitrogen and oxygen react together.

....................................................................................................................................

....................................................................................................................................

(iii) What is the main environmental effect of the presence of nitrogen oxides in the atmosphere?

....................................................................................................................................[4]

(c) Describe and explain how the basicities of ethylamine and phenylamine compare to that of ammonia.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[4]

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(d) Compound X is a useful intermediate in the synthesis of pharmaceuticals. X can be synthesised from chloromethylbenzene according to the following scheme.

T W

step 1

step 3 step 4

step 5

X

CH2Cl step 2CH2CN

CH2CH2NH CH2

CH2CO2H

O

C

(i) What type of reaction is each of the following?

step 1 .........................................................................................................................

step 2 .........................................................................................................................

(ii) Suggest reagents and conditions for

step 1, ........................................................................................................................

step 2. ........................................................................................................................

(iii) Draw the structures of the intermediates T and W in the boxes above.[6]

[Total: 15]

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5 (a) A series of experiments is carried out in which the reagent shown at the top of the column of the table is mixed, in turn, with each of the reagents at the side.

Complete the following table by writing in each box the formula of any gas produced. Write x in the box if no gas is produced. The fi rst column has been completed as an illustration.

H2O

OH CO2H OH

Na H2

KOH(aq) x

Na2CO3(aq) x

[5]

(b) Compound C is responsible for the pleasant aroma of apples. It can be prepared from phenol by the following 3-step synthesis.

OH OH

C

A

CH3H3CCH3

step1

OH

C

B

CH3H3CCH3

step2

O

O

C

C

CH3

CH3

H3CCH3

step3

(i) The only by-product of step 1 is HCl. Suggest the reagent that was used to react with phenol to produce compound A.

....................................................................................................................................

(ii) What type of reaction is occurring in step 2?

....................................................................................................................................

(iii) What reagents and conditions are required for step 3?

....................................................................................................................................

(iv) State the reagent and conditions needed to convert C back to B, the reverse ofstep 3.

....................................................................................................................................[5]

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(c) (i) Either compound A or compound B, or both, react with the following reagents. For each reagent draw the structure of the organic product formed with A, and with

B. If no reaction occurs, write ‘no reaction’ in the relevant box.

reagent and conditions product with A product with B

an excess of Br2(aq)

heat with HBr

pass vapour overheated Al 2O3

heat with acidifi ed K2Cr2O7

(ii) Choose one of the above reactions to enable you to distinguish between A and B.

State below the observations you would make with each compound.

reagent observation with A observation with B

[7]

[Total: 17]

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Section B



(a) Complete the table placing a tick ( ) in the correct column to indicate in which process each substance could be used.


adenine

alanine

aspartate

phosphate[3]

(b) Proteins and DNA form different helical structures. Briefl y describe the bonding that maintains the shape of each of these helical structures.

protein ...............................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

DNA ..................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[4]

(c) Describe the differences in bonding in the primary and tertiary structures of proteins. Your answer should include reference both to the nature of the bonding and the types of amino acid causing it.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[3]

[Total: 10]

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7 Modern methods of analysis have had far-reaching effects on a number of branches of science including medicine, forensic science, environmental monitoring and archaeology.

(a) Outline, in simple terms, the technique of DNA fi ngerprinting.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[4]

(b) Complete the table by indicating whether the items can be used for DNA fi ngerprinting. Use a tick ( ) for items which can be used for DNA fi ngerprinting and a cross (x) for items

which cannot.

item for testing suitable for DNA fi ngerprinting

human hair

piece of a fl int tool

piece of Iron Age pot

piece of Roman leather

[3]

(c) Various forms of chromatography can be used to separate and analyse mixtures.HPLC (high performance liquid chromatography) can be used to separate each of the following mixtures. State another method of chromatography which would separate each mixture.

insecticides in a sample of water ......................................................................................

dyes present in a foodstuff ...............................................................................................

drug residue in an athlete’s urine .....................................................................................[3]

[Total: 10]

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8 In recent years there has been a lot of interest in polymers in the form of gels that absorb aqueous materials. One of the largest uses of these polymers is in disposable nappies (diapers). The gel which is used in this case is a polymer of propenoic acid.

O

OH

propenoic acid

(a) (i) Draw a section of the polymer of propenoic acid showing two repeat units.

(ii) By what type of chemical reaction is this polymer formed?

....................................................................................................................................

(iii) By what type of bonding is water held on the polymer?

....................................................................................................................................[3]

(b) For some disposable nappies (diapers), the monomer is a mixture of propenoic acid and sodium propenoate. The properties of the polymer are infl uenced by the proportion of sodium salt in the monomer mixture.

(i) Suggest and explain how the difference in the structure of this polymer compared to one formed only from propenoic acid might affect the water absorbing properties of the polymer.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

(ii) Suggest a property the polymer should have in order to be used in disposable products.

....................................................................................................................................[3]

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(c) A variation on the gel used for disposable nappies (diapers) containing more sodium propenoate has been used to treat soils contaminated by heavy metals such as lead (Pb2+) and cadmium (Cd2+). Suggest why the gel is effective.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[2]

(d) Another variation on this type of polymer is used in hair gels. In these, the polymer chains are cross-linked by a compound known as pentaerythritol.

OH

OH

HO

HO

pentaerythritol

(i) By what type of chemical reaction are the cross-links in this polymer formed?

....................................................................................................................................

(ii) It is important that the gel should be easily washed out of hair. What is it about the structure of the polymer that allows this to happen?

....................................................................................................................................[2]

[Total: 10]

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Electronic calculators may be used.You may lose marks if you do not show your working or if you do not useappropriate units.A Data Booklet is provided.


CHEMISTRY 9701/41

Paper 4 Structured Questions October/November 2013

2 hours






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Section A


1 (a) Gaseous ammonia reacts with gaseous hydrogen chloride to form solid ammonium chloride.

NH3 + HCl → NH4Cl

The bonding in ammonium chloride includes ionic, covalent and co-ordinate (dative covalent) bonds.

Complete the following ‘dot-and-cross’ diagram of the bonding in ammonium chloride. For each of the six atoms show all the electrons in its outer shell. Three electrons have already been included.

Use the following code for your electrons.

electrons from chlorine x electrons from hydrogen o electrons from nitrogen

H H

H

N Cl

H

+

–

xo

[3]

(b) When a sample of dry ammonia is needed in the laboratory, the gas is passed through a tower containing lumps of solid calcium oxide, CaO.

(i) Suggest why the usual drying agent for gases, concentrated H2SO4, is not used for ammonia.

....................................................................................................................................

(ii) Write an equation for the reaction between CaO and H2O.

....................................................................................................................................

(iii) Suggest why CaO rather than MgO is used to dry ammonia.

....................................................................................................................................[3]

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(c) (i) Write an equation showing the thermal decomposition of calcium nitrate, Ca(NO3)2.

....................................................................................................................................

(ii) State and explain how the thermal stabilities of the nitrates vary down Group II.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[4]

[Total: 10]

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2 (a) The melting points of some Group IV elements are given below.

element melting point / K

C 3925

Si 1683

Ge 1210

Sn 505

Suggest an explanation for each of the following.

(i) The melting point of silicon is less than that of carbon.

....................................................................................................................................

....................................................................................................................................

(ii) The melting point of tin is less than that of germanium.

....................................................................................................................................

....................................................................................................................................[2]

(b) Using data from the Data Booklet where appropriate, write equations for the following reactions of compounds of Group IV elements.

(i) SiCl 4(l) + H2O(l)

....................................................................................................................................

(ii) the action of heat on PbCl 4(l)

....................................................................................................................................

(iii) SnCl 2(aq) + FeCl 3(aq)

....................................................................................................................................

(iv) SnO2(s) + NaOH(aq)

....................................................................................................................................[4]

[Total: 6]

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3 (a) (i) Using the symbol HZ to represent a Brønsted-Lowry acid, write equations which show the following substances acting as Brønsted-Lowry bases.

NH3 + →

CH3OH + →

(ii) Using the symbol B– to represent a Brønsted-Lowry base, write equations which show the following substances acting as Brønsted-Lowry acids.

NH3 + →

CH3OH + →

[4]

(b) State briefl y what is meant by the following terms.

(i) reversible reaction

....................................................................................................................................

(ii) dynamic equilibrium

....................................................................................................................................

....................................................................................................................................[2]

(c) (i) Explain what is meant by a buffer solution.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

(ii) Explain how the working of a buffer solution relies on a reversible reaction involving a Brønsted-Lowry acid such as HZ and a Brønsted-Lowry base such as Z–.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[4]

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(d) Propanoic acid, CH3CH2CO2H, is a weak acid with Ka = 1.34 × 10–5 mol dm–3.

(i) Calculate the pH of a 0.500 mol dm–3 solution of propanoic acid.

Buffer solution F was prepared by adding 0.0300 mol of sodium hydroxide to 100 cm3 of a 0.500 mol dm–3 solution of propanoic acid.

(ii) Write an equation for the reaction between sodium hydroxide and propanoic acid.

....................................................................................................................................

(iii) Calculate the concentrations of propanoic acid and sodium propanoate in buffer solution F.

[propanoic acid] = ................................ mol dm–3

[sodium propanoate] = ................................ mol dm–3

(iv) Calculate the pH of buffer solution F.

pH = ................................[6]

(e) Phenyl propanoate cannot be made directly from propanoic acid and phenol. Suggest the identities of the intermediate G, the reagent H and the by-product J in the

following reaction scheme.

O

ONa

O+ JGCH3CH2CO2H

H

G is ..........................................................

H is ..........................................................

J is ..........................................................[2]

[Total: 18]

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4 (a) Explain what is meant by the term bond energy.

...........................................................................................................................................

...........................................................................................................................................[2]

(b) (i) Describe and explain the trend in bond energies of the C–X bond in halogenoalkanes, where X = F, Cl, Br or I.

....................................................................................................................................

....................................................................................................................................

(ii) Describe the relationship between the reactivity of halogenoalkanes, RX, and the bond energies of the C–X bond.

....................................................................................................................................

....................................................................................................................................[3]

(c) Use the Data Booklet to suggest an explanation as to why CFCs such as CF2Cl 2 are much more harmful to the ozone layer than fl uorocarbons such as CF4 or hydrocarbons such as butane, C4H10.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[3]

(d) Predict the products of the following reactions and draw their structures in the boxes below. The molecular formula of each product is given, where X = Cl , Br or I.

H2O

C3H5O2X

+ Cl Cl

O

H2O

C3H7OX

+ I Cl

H2O

C7H7OX

+

Br

Br

[3]

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(e) Ethane reacts with chlorine according to the following equation.

C2H6 + Cl 2 → C2H5Cl + HCl

(i) State the conditions needed for this reaction.

....................................................................................................................................

(ii) State the type of reaction occurring here.

....................................................................................................................................

One of the steps during this reaction is the following process.

Cl + CH3CH3 → HCl + CH3CH2

(iii) Use the Data Booklet to calculate the enthalpy change, ∆H, of this step.

∆H = ................................ kJ mol–1

(iv) Use the Data Booklet to calculate the enthalpy change, ∆H, of the similar reaction:

I + CH3CH3 → HI + CH3CH2

∆H = ................................ kJ mol–1

(v) Hence suggest why it is not possible to make iodoethane by reacting together iodine and ethane.

....................................................................................................................................

(vi) Complete the following equations of some possible steps in the formation of chloroethane.

Cl 2 → ..............


CH3CH2 + .............. → ........................ + ..............

.............. + .............. → CH3CH2Cl[8]

[Total: 19]

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5 Super-absorbent polymers have the ability to absorb 200-300 times their own mass of water. They are classifi ed as hydrogels and they are widely used in personal disposable hygiene products such as babies’ nappies (diapers).

These polymers are commonly made by the polymerisation of compound K mixed with sodium hydroxide in the presence of an initiator.

CH2 C

H

CO2HK

(a) (i) Explain what is meant by the term polymerisation.

....................................................................................................................................

....................................................................................................................................

(ii) What type of polymerisation is involved in the formation of hydrogels?

....................................................................................................................................

(iii) Describe the changes in chemical bonding that occur during the polymerisation of K.

....................................................................................................................................

....................................................................................................................................[3]

(b) Acrylic acid is the common name for compound K. Suggest the systematic (chemical) name of K.

...........................................................................................................................................[1]

(c) (i) Draw the structure of at least two repeat units of the polymer formed by the above method from acrylic acid, K, when mixed with NaOH.

(ii) The C–C–C bond angle in compound K changes when the polymer is formed. State and explain how the C–C–C bond angle differs between a molecule of K and

the polymer.

angle changes from ............................................ to .................................................

explanation ................................................................................................................

....................................................................................................................................[4]

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(d) (i) Draw a detailed diagram of a portion of the polymer you have drawn in (c)(i) to explain how it can absorb a large volume of water.

(ii) A student added 0.10 g of the polymer to 10 cm3 of aqueous copper(II) sulfate solution.

Predict, with a reason, what you expect to observe.

....................................................................................................................................

....................................................................................................................................[4]

(e) Compound L, CH2=CHCONH2, can also be polymerised to form a super-absorbent polymer.

(i) Name the two functional groups in compound L.

....................................................................................................................................

....................................................................................................................................

Compound K can be converted into compound L by the following two-step route.

H2C CO2H

HC

H2C CO2–NH4

+

HC

K

H2C CONH2

HC

L

step 1 step 2

(ii) Suggest a reagent for step 1.

....................................................................................................................................

(iii) What other product is formed in step 2?

....................................................................................................................................

(iv) State the reagents and conditions necessary to re-form K from L.

....................................................................................................................................[5]

[Total: 17]

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Section B


6 (a) Protein molecules are formed by the polymerisation of amino acids in the body. The structures of three amino acids are given.

OHH2N

O

OHHO

NH2

O

OH

NH2

O

glycine (gly) serine (ser) valine (val)

(i) How many different tripeptides can be made using one molecule of each of the amino acids shown?

....................................................................................................................................

(ii) Draw the tripeptide ser-gly-val, showing the peptide bonds in displayed form.

(iii) Within the tripeptide, which amino acid provides a hydrophobic side chain?

....................................................................................................................................

(iv) Polypeptide chains can form bonds giving proteins their secondary and tertiary structures.

Using the tripeptide in (ii), state two types of bonding that can be formed and the groups in the tripeptide that are involved in this bonding.

bond .................................................... groups ........................................................

bond .................................................... groups ........................................................[6]

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(b) Enzymes are particular types of proteins that catalyse chemical reactions. The effi ciency of enzymes can be reduced by the presence of other molecules known as inhibitors.

Explain how both competitive and non-competitive inhibitors prevent enzymes from working effi ciently.

(i) competitive inhibitors .................................................................................................

....................................................................................................................................

....................................................................................................................................

(ii) non-competitive inhibitors ..........................................................................................

....................................................................................................................................

....................................................................................................................................

(iii) The graph shows the rate of an enzyme-catalysed reaction against the substrate concentration in the absence of an inhibitor.

rate ofreaction

concentration of substrate

On the same axes, sketch a graph showing the rate of this reaction if anon-competitive inhibitor was present.

[4]

[Total: 10]

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7 Electrophoresis is a technique which can be used to separate amino acids or peptide fragments present in a mixture.

(a) Draw a diagram to show the apparatus used to carry out electrophoresis. You should label each of the relevant parts of the apparatus.

[4]

(b) How far an amino acid will travel during electrophoresis depends on the pH of the solution. For a given potential difference, state two other factors that will affect how far a given

amino acid travels in a fi xed time during electrophoresis.

1. .......................................................................................................................................

...........................................................................................................................................

2. .......................................................................................................................................

...........................................................................................................................................[2]

(c) A number of analytical and separation techniques rely on substances having different partition coeffi cients.

State what is meant by the term partition coeffi cient.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[1]

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(d) The partition coeffi cient of X between ethoxyethane and water is 40.0. A solution contains 4.00 g of X dissolved in 0.500 dm3 of water.

Calculate the mass of X that can be extracted from this aqueous solution by shaking it with

(i) 0.050 dm3 of ethoxyethane,

(ii) two successive portions of 0.025 dm3 of ethoxyethane.

[4]

[Total: 11]

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8 In a world with a rapidly increasing population, access to clean drinking water is critical. For many countries, groundwater sources, rather than stored rainwater or river-water, are vital. Groundwater is water that exists in the pore spaces and fractures in rock and sediment beneath the Earth's surface. The World Health Organisation (WHO) provides maximum recommended concentrations for different ions present in drinking water.

(a) The geological nature of the soil determines the chemical composition of the groundwater. The table shows some ions which may contaminate groundwater.

ion present WHO maximum permittedconcentration / mg dm–3

Ba2+ 0.30

Cl – 250.00

NO3– 50.00

Pb2+ 0.01

Na+ 20.00

SO42– 500.00

(i) Nitrate, NO3–, ions are diffi cult to remove from groundwater.

What is the reason for this?

....................................................................................................................................

(ii) State which ions in the table above are likely to be removed from the water by treatment with powdered limestone, CaCO3, giving reasons for each of your answers.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[4]

(b) Nitrates and phosphates can enter water courses such as rivers or streams as a result of human activity. Both of these ions are nutrients for algae.

(i) What is the origin of these nitrates?

....................................................................................................................................

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(ii) Suggest an origin for the phosphates found in water courses.

....................................................................................................................................

(iii) What effect do nitrates and phosphates have on water courses?

....................................................................................................................................

....................................................................................................................................[3]

(c) Acid rain can have a major impact on natural waters, particularly lakes. In recent years there has been a worldwide effort to reduce the amount of acid rain produced.

(i) Write equations to show the production of acid rain from sulfur dioxide, SO2.

....................................................................................................................................

....................................................................................................................................

(ii) The use of fossil fuels is one major source of sulfur dioxide. Name another major industrial source.

....................................................................................................................................[2]

[Total: 9]

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CHEMISTRY 9701/42


2 hours





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*5507470235*


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Section A


1 (a) Gaseous ammonia reacts with gaseous hydrogen chloride to form solid ammonium chloride.

NH3 + HCl → NH4Cl

The bonding in ammonium chloride includes ionic, covalent and co-ordinate (dative covalent) bonds.

Complete the following ‘dot-and-cross’ diagram of the bonding in ammonium chloride. For each of the six atoms show all the electrons in its outer shell. Three electrons have already been included.


electrons from chlorine x electrons from hydrogen o electrons from nitrogen

H H

H

N Cl

H

+

–

xo

[3]

(b) When a sample of dry ammonia is needed in the laboratory, the gas is passed through a tower containing lumps of solid calcium oxide, CaO.

(i) Suggest why the usual drying agent for gases, concentrated H2SO4, is not used for ammonia.

....................................................................................................................................

(ii) Write an equation for the reaction between CaO and H2O.

....................................................................................................................................

(iii) Suggest why CaO rather than MgO is used to dry ammonia.

....................................................................................................................................[3]

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(c) (i) Write an equation showing the thermal decomposition of calcium nitrate, Ca(NO3)2.

....................................................................................................................................

(ii) State and explain how the thermal stabilities of the nitrates vary down Group II.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[4]

[Total: 10]

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2 (a) The melting points of some Group IV elements are given below.

element melting point / K

C 3925

Si 1683

Ge 1210

Sn 505

Suggest an explanation for each of the following.

(i) The melting point of silicon is less than that of carbon.

....................................................................................................................................

....................................................................................................................................

(ii) The melting point of tin is less than that of germanium.

....................................................................................................................................

....................................................................................................................................[2]


(i) SiCl 4(l) + H2O(l)

....................................................................................................................................

(ii) the action of heat on PbCl 4(l)

....................................................................................................................................

(iii) SnCl 2(aq) + FeCl 3(aq)

....................................................................................................................................

(iv) SnO2(s) + NaOH(aq)

....................................................................................................................................[4]

[Total: 6]

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3 (a) (i) Using the symbol HZ to represent a Brønsted-Lowry acid, write equations which show the following substances acting as Brønsted-Lowry bases.

NH3 + →

CH3OH + →

(ii) Using the symbol B– to represent a Brønsted-Lowry base, write equations which show the following substances acting as Brønsted-Lowry acids.

NH3 + →

CH3OH + →

[4]

(b) State briefl y what is meant by the following terms.

(i) reversible reaction

....................................................................................................................................

(ii) dynamic equilibrium

....................................................................................................................................

....................................................................................................................................[2]

(c) (i) Explain what is meant by a buffer solution.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

(ii) Explain how the working of a buffer solution relies on a reversible reaction involving a Brønsted-Lowry acid such as HZ and a Brønsted-Lowry base such as Z–.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[4]

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(d) Propanoic acid, CH3CH2CO2H, is a weak acid with Ka = 1.34 × 10–5 mol dm–3.

(i) Calculate the pH of a 0.500 mol dm–3 solution of propanoic acid.

Buffer solution F was prepared by adding 0.0300 mol of sodium hydroxide to 100 cm3 of a 0.500 mol dm–3 solution of propanoic acid.

(ii) Write an equation for the reaction between sodium hydroxide and propanoic acid.

....................................................................................................................................

(iii) Calculate the concentrations of propanoic acid and sodium propanoate in buffer solution F.

[propanoic acid] = ................................ mol dm–3

[sodium propanoate] = ................................ mol dm–3

(iv) Calculate the pH of buffer solution F.

pH = ................................[6]

(e) Phenyl propanoate cannot be made directly from propanoic acid and phenol. Suggest the identities of the intermediate G, the reagent H and the by-product J in the

following reaction scheme.

O

ONa

O+ JGCH3CH2CO2H

H

G is ..........................................................

H is ..........................................................

J is ..........................................................[2]

[Total: 18]

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4 (a) Explain what is meant by the term bond energy.

...........................................................................................................................................

...........................................................................................................................................[2]

(b) (i) Describe and explain the trend in bond energies of the C–X bond in halogenoalkanes, where X = F, Cl, Br or I.

....................................................................................................................................

....................................................................................................................................

(ii) Describe the relationship between the reactivity of halogenoalkanes, RX, and the bond energies of the C–X bond.

....................................................................................................................................

....................................................................................................................................[3]

(c) Use the Data Booklet to suggest an explanation as to why CFCs such as CF2Cl 2 are much more harmful to the ozone layer than fl uorocarbons such as CF4 or hydrocarbons such as butane, C4H10.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[3]

(d) Predict the products of the following reactions and draw their structures in the boxes below. The molecular formula of each product is given, where X = Cl , Br or I.

H2O

C3H5O2X

+ Cl Cl

O

H2O

C3H7OX

+ I Cl

H2O

C7H7OX

+

Br

Br

[3]

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(e) Ethane reacts with chlorine according to the following equation.

C2H6 + Cl 2 → C2H5Cl + HCl

(i) State the conditions needed for this reaction.

....................................................................................................................................

(ii) State the type of reaction occurring here.

....................................................................................................................................

One of the steps during this reaction is the following process.


(iii) Use the Data Booklet to calculate the enthalpy change, ∆H, of this step.

∆H = ................................ kJ mol–1

(iv) Use the Data Booklet to calculate the enthalpy change, ∆H, of the similar reaction:

I + CH3CH3 → HI + CH3CH2

∆H = ................................ kJ mol–1

(v) Hence suggest why it is not possible to make iodoethane by reacting together iodine and ethane.

....................................................................................................................................

(vi) Complete the following equations of some possible steps in the formation of chloroethane.

Cl 2 → ..............


CH3CH2 + .............. → ........................ + ..............

.............. + .............. → CH3CH2Cl[8]

[Total: 19]

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5 Super-absorbent polymers have the ability to absorb 200-300 times their own mass of water. They are classifi ed as hydrogels and they are widely used in personal disposable hygiene products such as babies’ nappies (diapers).

These polymers are commonly made by the polymerisation of compound K mixed with sodium hydroxide in the presence of an initiator.

CH2 C

H

CO2HK

(a) (i) Explain what is meant by the term polymerisation.

....................................................................................................................................

....................................................................................................................................

(ii) What type of polymerisation is involved in the formation of hydrogels?

....................................................................................................................................

(iii) Describe the changes in chemical bonding that occur during the polymerisation of K.

....................................................................................................................................

....................................................................................................................................[3]

(b) Acrylic acid is the common name for compound K. Suggest the systematic (chemical) name of K.

...........................................................................................................................................[1]

(c) (i) Draw the structure of at least two repeat units of the polymer formed by the above method from acrylic acid, K, when mixed with NaOH.

(ii) The C–C–C bond angle in compound K changes when the polymer is formed. State and explain how the C–C–C bond angle differs between a molecule of K and

the polymer.

angle changes from ............................................ to .................................................

explanation ................................................................................................................

....................................................................................................................................[4]

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(d) (i) Draw a detailed diagram of a portion of the polymer you have drawn in (c)(i) to explain how it can absorb a large volume of water.

(ii) A student added 0.10 g of the polymer to 10 cm3 of aqueous copper(II) sulfate solution.

Predict, with a reason, what you expect to observe.

....................................................................................................................................

....................................................................................................................................[4]

(e) Compound L, CH2=CHCONH2, can also be polymerised to form a super-absorbent polymer.

(i) Name the two functional groups in compound L.

....................................................................................................................................

....................................................................................................................................

Compound K can be converted into compound L by the following two-step route.

H2C CO2H

HC

H2C CO2–NH4

+

HC

K

H2C CONH2

HC

L

step 1 step 2

(ii) Suggest a reagent for step 1.

....................................................................................................................................

(iii) What other product is formed in step 2?

....................................................................................................................................

(iv) State the reagents and conditions necessary to re-form K from L.

....................................................................................................................................[5]

[Total: 17]

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Section B


6 (a) Protein molecules are formed by the polymerisation of amino acids in the body. The structures of three amino acids are given.

OHH2N

O

OHHO

NH2

O

OH

NH2

O

glycine (gly) serine (ser) valine (val)

(i) How many different tripeptides can be made using one molecule of each of the amino acids shown?

....................................................................................................................................

(ii) Draw the tripeptide ser-gly-val, showing the peptide bonds in displayed form.

(iii) Within the tripeptide, which amino acid provides a hydrophobic side chain?

....................................................................................................................................

(iv) Polypeptide chains can form bonds giving proteins their secondary and tertiary structures.

Using the tripeptide in (ii), state two types of bonding that can be formed and the groups in the tripeptide that are involved in this bonding.

bond .................................................... groups ........................................................

bond .................................................... groups ........................................................[6]

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(b) Enzymes are particular types of proteins that catalyse chemical reactions. The effi ciency of enzymes can be reduced by the presence of other molecules known as inhibitors.

Explain how both competitive and non-competitive inhibitors prevent enzymes from working effi ciently.

(i) competitive inhibitors .................................................................................................

....................................................................................................................................

....................................................................................................................................

(ii) non-competitive inhibitors ..........................................................................................

....................................................................................................................................

....................................................................................................................................


rate ofreaction


On the same axes, sketch a graph showing the rate of this reaction if anon-competitive inhibitor was present.

[4]

[Total: 10]

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7 Electrophoresis is a technique which can be used to separate amino acids or peptide fragments present in a mixture.

(a) Draw a diagram to show the apparatus used to carry out electrophoresis. You should label each of the relevant parts of the apparatus.

[4]

(b) How far an amino acid will travel during electrophoresis depends on the pH of the solution. For a given potential difference, state two other factors that will affect how far a given

amino acid travels in a fi xed time during electrophoresis.

1. .......................................................................................................................................

...........................................................................................................................................

2. .......................................................................................................................................

...........................................................................................................................................[2]

(c) A number of analytical and separation techniques rely on substances having different partition coeffi cients.

State what is meant by the term partition coeffi cient.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[1]

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(d) The partition coeffi cient of X between ethoxyethane and water is 40.0. A solution contains 4.00 g of X dissolved in 0.500 dm3 of water.

Calculate the mass of X that can be extracted from this aqueous solution by shaking it with

(i) 0.050 dm3 of ethoxyethane,

(ii) two successive portions of 0.025 dm3 of ethoxyethane.

[4]

[Total: 11]

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8 In a world with a rapidly increasing population, access to clean drinking water is critical. For many countries, groundwater sources, rather than stored rainwater or river-water, are vital. Groundwater is water that exists in the pore spaces and fractures in rock and sediment beneath the Earth's surface. The World Health Organisation (WHO) provides maximum recommended concentrations for different ions present in drinking water.

(a) The geological nature of the soil determines the chemical composition of the groundwater. The table shows some ions which may contaminate groundwater.

ion present WHO maximum permittedconcentration / mg dm–3

Ba2+ 0.30

Cl – 250.00

NO3– 50.00

Pb2+ 0.01

Na+ 20.00

SO42– 500.00

(i) Nitrate, NO3–, ions are diffi cult to remove from groundwater.

What is the reason for this?

....................................................................................................................................

(ii) State which ions in the table above are likely to be removed from the water by treatment with powdered limestone, CaCO3, giving reasons for each of your answers.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[4]

(b) Nitrates and phosphates can enter water courses such as rivers or streams as a result of human activity. Both of these ions are nutrients for algae.

(i) What is the origin of these nitrates?

....................................................................................................................................

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(ii) Suggest an origin for the phosphates found in water courses.

....................................................................................................................................

(iii) What effect do nitrates and phosphates have on water courses?

....................................................................................................................................

....................................................................................................................................[3]

(c) Acid rain can have a major impact on natural waters, particularly lakes. In recent years there has been a worldwide effort to reduce the amount of acid rain produced.

(i) Write equations to show the production of acid rain from sulfur dioxide, SO2.

....................................................................................................................................

....................................................................................................................................

(ii) The use of fossil fuels is one major source of sulfur dioxide. Name another major industrial source.

....................................................................................................................................[2]

[Total: 9]







CHEMISTRY 9701/43


2 hours






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ForExaminer’s

Use

Section A


1 (a) The nitrate ion, NO3–, contains a dative covalent bond.

Complete the following ‘dot-and-cross’ diagram of the bonding in the nitrate ion. For each of the four atoms show all the electrons in its outer shell. Three electrons have already been included.


electrons from oxygen x electrons from nitrogen added electron(s) responsible for the overall negative charge

N

O

O

O

x

–

[3]

(b) (i) Write an equation showing the action of heat on magnesium nitrate, Mg(NO3)2.

....................................................................................................................................

(ii) Describe and explain the trend that is observed in the thermal stabilities of theGroup II nitrates.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[4]

(c) When concentrated nitric acid, HNO3, is added to copper turnings, a brown gas is evolved. Use data from the Data Booklet to construct an ionic equation for this reaction.

...........................................................................................................................................

...........................................................................................................................................[2]

[Total: 9]

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2 (a) State two assumptions of the kinetic theory of gases, as applied to ideal gases.

...........................................................................................................................................

...........................................................................................................................................[2]

(b) (i) State the conditions of temperature and pressure under which real gases behave least like an ideal gas.

....................................................................................................................................

(ii) Explain why real gases do not behave ideally under these conditions.

....................................................................................................................................

....................................................................................................................................[2]

(c) Gaseous aluminium chloride is dimeric at low temperatures, but the dimer dissociates on heating.

Al 2Cl 6(g) 2Al Cl 3(g)

(i) State whether this dissociation is endothermic or exothermic. Explain your answer.

....................................................................................................................................

....................................................................................................................................

(ii) Choose one reaction in organic chemistry that is catalysed by Al Cl 3, and write the structural formulae of the reactants and products in the boxes below.

Al Cl 3

[3]

[Total: 7]

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3 (a) Write equations, with state symbols, to defi ne the following.

(i) the C–Br bond energy in CH3Br

....................................................................................................................................

(ii) the Al –Cl bond energy in Al Cl 3

....................................................................................................................................[3]

(b) (i) Describe and explain the trend in bond energies of the bonds in Cl 2, Br2 and I2.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

(ii) Fluorine, F2, does not follow this trend. Suggest a possible reason why.

....................................................................................................................................

....................................................................................................................................[3]

(c) (i) Use data from the Data Booklet to calculate the enthalpy change of the following reaction.

H2(g) + X2(g) → 2HX(g)

when X = Cl

∆H = ........................ kJ mol–1

when X = I

∆H = ........................ kJ mol–1

(ii) Use these results to describe and explain the trend in the thermal stabilities of the hydrides of Group VII.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[5]

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(d) Bromine reacts with hot NaOH(aq) to give a solution which on cooling produces white crystals of compound A.

A has the following percentage composition by mass: Na, 15.2; O, 31.8; Br, 53.0.

The remaining solution contains mostly NaBr, with a little of compound A.

(i) Calculate the empirical formula of A.

(ii) Construct an equation for the reaction between Br2 and hot NaOH(aq).

....................................................................................................................................[4]

[Total: 15]

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4 (a) The electrical conductivities of some Group IV elements are given below.

element electricalconductivity / Ω–1

cm–1

C (graphite) 6.1 × 102

Si 2.5 × 10–6

Ge 1.5 × 10–2

Sn 9.2 × 104

From a consideration of the structures, suggest reasons for the following.

(i) The electrical conductivity of silicon is less than that of graphite.

....................................................................................................................................

....................................................................................................................................

(ii) The electrical conductivity of tin is more than that of germanium.

....................................................................................................................................

....................................................................................................................................[2]


(i) the action of heat on PbO2(s)

....................................................................................................................................

(ii) PbO2(s) + HCl (aq)

....................................................................................................................................

(iii) SnO(s) + NaOH(aq)

....................................................................................................................................

(iv) GeCl 4(l) + H2O(l)

....................................................................................................................................[4]

[Total: 6]

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5 (a) Bromine reacts with a variety of organic compounds. For each of the following reactions,

complete and balance the equation, including the structural formula of the organic product,

state the specific conditions (if any) under which the reaction takes place and the type of reaction that occurs.

(i) ............Br2 +

OH

reaction conditions .....................................................................................................

type of reaction ..........................................................................................................

(ii) ............Br2 +


type of reaction ..........................................................................................................

(iii) ............Br2 +


type of reaction ..........................................................................................................[10]

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(b) When hydrocarbon B is heated with concentrated manganate(VII) ions, three organic compounds, C, D and E, are formed.

B

hot MnO4–

C

D

E

(i) Suggest the identities of compounds C, D and E, drawing their structures in the boxes above.

(ii) Use the relevant letter, C, D or E, to identify which of your compounds will react with each of the following reagents.

Each reagent may react with more than one of C, D and E, in which case state all the compounds that may react with each reagent.

2,4-dinitrophenylhydrazine ..............................

alkaline aqueous iodine ...................................

aqueous sodium hydroxide ..............................[6]

[Total: 16]

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6 Naturally-occurring α-amino acids, RCH(NH2)CO2H, can be classifi ed as amphiprotic substances. An amphiprotic substance is one which can act as both a Brønsted-Lowry acid and base.

α-amino acid R group

alanine CH3–

aspartic acid HO2CCH2–

glycine H–

lysine H2N(CH2)4–

threonine CH3CH(OH)–

serine HOCH2–

(a) What is the Brønsted-Lowry defi nition of an acid?

...........................................................................................................................................

...........................................................................................................................................[1]

(b) (i) All α-amino acids are soluble in water since they can form hydrogen bonds with water molecules and can also exist as zwitterions.

Draw diagrams to show how the carboxylic acid and amino groups of alanine can form hydrogen bonds with water molecules.

O OC

H

carboxylic acid

H HN

amino group

(ii) Draw the structure of the zwitterionic form of glycine.

[5]

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(c) The amino acid alanine can be formed by the reaction of CH3CHCl CO2H with an excess of ammonia.

Outline a mechanism for this reaction using curly arrows.

[3]

(d) Amino acids can form different ions at different pH values. Suggest the structures of the ions formed from the α-amino acids below at the respective

pH value.

lysine at pH 1 aspartic acid at pH 14

[2]

(e) (i) How many different dipeptides is it possible to synthesise, each containing two of the three amino acids alanine, serine and lysine?

......................................

(ii) Write the structural formula of one of these dipeptides incorporating serine and alanine.

[3]

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(f) Most naturally-occurring amino acids have a chiral centre and exhibit stereoisomerism.

(i) Defi ne the term stereoisomerism.

....................................................................................................................................

....................................................................................................................................

There are four optical isomers of threonine.

Some of these optical isomers are drawn below.

H

H2N

HO2C

CH3

OH

HF

H

H2N

HO2C CH3

OH

HG

H

H2N

HO2C CH3

H

OHH

H

H2N

HO2C CH3

H

OH

J

When answering this question, remember that completely free rotation about a C–C single bond occurs in these compounds.

(ii) Which of the structures G, H or J is identical to structure F? ....................................

(iii) The other two of the structures G, H or J represent two of the three other possible optical isomers of threonine.

Complete the following partial structure of the fourth optical isomer.

H CH3

[3]

[Total: 17]

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Section B


7 (a) Enzymes are particular types of proteins that catalyse chemical reactions. The effi ciency of enzymes can be reduced by the presence of other substances known as inhibitors.

(i) State one example of a substance that can act as a non-competitive inhibitor in enzyme reactions.

....................................................................................................................................

(ii) For the inhibitor you have identifi ed, explain why it is a non-competitive inhibitor.

....................................................................................................................................

....................................................................................................................................


rate ofreaction


On the same axes, sketch a graph showing the rate of this reaction if a competitive inhibitor was present.

[4]

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(b) DNA is responsible for encoding the amino acid sequence to produce proteins.

Ribosome, tRNA and mRNA are all involved in the process of protein synthesis.

(i) Write ribosome, tRNA and mRNA in the boxes below to show the correct sequence in which they are involved.

DNA protein

(ii) Sequences of three bases code for specifi c amino acids. The code UGA however does not usually code for an amino acid. Suggest its use.

....................................................................................................................................[3]

(c) Much of the energy used in biochemical reactions is provided by the hydrolysis of the molecule ATP.

(i) What are the breakdown products of the hydrolysis of ATP?

....................................................................................................................................

(ii) Give two uses for the energy released by ATP hydrolysis in cells.

1. ................................................................................................................................

2. ................................................................................................................................[3]

[Total: 10]

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8 Instrumental analysis plays an increasingly important role in modern chemistry. Two important techniques are NMR spectroscopy and X-ray crystallography.

(a) Both techniques use part of the electromagnetic spectrum. Which technique uses radiation with the longer wavelength, and in which part of the

spectrum is it found?

...........................................................................................................................................[1]

(b) NMR spectroscopy provides detailed information about protons, but X-ray crystallography is unable to detect them. Explain these facts.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[2]

(c) The protein found in hair contains the amino acid cysteine, C3H7SNO2. Crystalline cysteine was examined using X-ray crystallography. State which atom produced the strongest refl ection, explaining your answer.

...........................................................................................................................................

...........................................................................................................................................[1]

(d) Compound P is an alcohol that can be converted into compound Q in the following reaction sequence.

P → CxH6O → Q

Spectral analyses of P and Q were carried out.

(i) The mass spectrum of P shows an M : M+1 peak ratio of 4.5 : 0.15. Calculate the number of carbon atoms in P.

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The NMR spectra of P and Q are shown below.

11 10 9 8 7 6 5 4 3 2 1 0δ / ppm

12 10 8 6 4 2 0δ / ppm

P

Q

(ii) In the spectrum of P, clearly label the peak due to the –OH group with an X.

(iii) State how many different proton environments are present in compound Q.

......................................

(iv) What evidence is there in these spectra that P is a primary rather than a secondary alcohol?

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................

(v) Draw a structure for Q.

[6]

[Total: 10]

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9 Until 1985, carbon was thought to exist in only two structural forms or allotropes. In 1985 another form, buckminsterfullerene, was discovered, in which the carbon exists as sphericalmolecules.

(a) The other two forms of carbon have very different structures.

(i) Name these two forms.

.............................................................. and ..............................................................

(ii) Give three differences in physical properties between these two forms.

....................................................................................................................................

....................................................................................................................................

....................................................................................................................................[4]

(b) The diagram shows the structure of buckminsterfullerene.

buckminsterfullerene

The molecule of buckminsterfullerene contains 60 carbon atoms. Suggest a reason why buckminsterfullerene reacts with hydrogen under suitable conditions and give a formula for the product.

...........................................................................................................................................

...........................................................................................................................................

...........................................................................................................................................[2]

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(c) In 2010, two scientists from the University of Manchester were awarded the Nobel Prize for Physics for their work on graphene, a new structural form of carbon. Graphene is one of the new ‘nano-materials’ being developed for commercial uses in the next10 years.

graphene

(i) Graphene is in the form of sheets of carbon one atom thick. Calculate the number of carbon atoms present in a sheet of graphene with a mass of one thousandth of a gram (0.001 g).

The number of hexagons in a large sheet of graphene can be assumed to be one half of the number of carbon atoms. Each hexagon has an area of 690 nm2.

(ii) Calculate the area of the sheet of graphene in (i).

area of sheet = .......................... nm2

(iii) Would you expect samples of graphene and buckminsterfullerene to be electrical conductors? Explain your answers.

graphene ...................................................................................................................

....................................................................................................................................

buckminsterfullerene .................................................................................................

....................................................................................................................................

[4]

[Total: 10]

06 9701 41 3RP - Weebly · 2018-09-09 · Reacting 100 g of alloy in this way produced 8.0 dm3 of...

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Transcript of 06 9701 41 3RP - Weebly · 2018-09-09 · Reacting 100 g of alloy in this way produced 8.0 dm3 of...