8 Themel I txperimentolChenristry

For each of the questions, there are four possible choices.Choose the one you consider correct and record your choice.

d 1. A substance is condensed using a water condenser. Whichof the following shows the melting and boiling points of thesubstance?

Melting poinV'C Boiling poinV'C

-1 15 -85

B -16.6 9.5

C -73 -10

D -1 30 36

d2. A mixture which contains a liquid and a soluble solid maybe separated by evaporation Which of the following is a

disadvantage of this method?

A lt always requires heating.B The liquid must have a high boiling point.

C The solute recovered may contain impurrties.D lt cannot be used for a solid with a low melting point.

()

d3. The following setup was used by a student t0 separate a

mixture of ethanol and water.

thermomster

water out

fractionatingcolumn

cold /water in

conical f'l

anti-bumpinggranule

Methods of Purificqtionond Anolysis

Which of the following is an error in the setup?

A A wrong container was used to collect the distillate.B The thermometer was placed too high in the fractionating

column.

C The conical f lask containing the distillate was enclosedwith a cork.

D The direction of flow of the water through the condenserwas wrong. (

)

4. A food dye is analysed by paper chromatography, giving thechromatogram shown:

start solvent front

0.0 .0 4.0 6.0 8.0 10.0 12.0 cm

d

d

\\,s

What is the B,value of the dye represented by the spot at8.0 cm?

A 0.60 B 0.67c 0.75 D 0.80 ( )

5. A sample of a compound, ally isocyanide, was made f rom an

experiment. This compound has been patented as a non-lethalweapon as it has an extremely penetrating and foul smell.

Which property of the compound can be used to check itspurity?

A Smell B ColourC Boiling point D Solubility in water

()

6. Which of the following can be used to separate a mercury-ethanol mixture?

MeltingpoinU"G

BoilingpoinU'C

Soluhitityin water

lVlercury -38 atr -1No

Ethanol -114 1B Yes

flask

liquidmrxture

A FiltrationC Separating funnel

B DistillationD Paper chromatography

()

theat

A

()

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round-bottomflask

\V0

\Vu

\\,s

1 . A student intends to separate a mixture of ethanol and waterusing the following apparatus:

ther:rnometer

water out retort stand

condenserflask

ethanoland watermlxture

cold /water in

tripodstand

Ethanol has a boiling point of 78.5"C and water has a boilingpoint of 1 00'C. He found thatthe liquid collected in the conicalf lask has a boiling point of 82'C.

He decided to make some changes and repeat the experiment.What change should he make t0 the experiment?

A lncrease the rate of heating.B Change the direction in which water enters the condenser.

C Add some porcelain chips to the liquid mixture in theround-bottom flask.

D lnsert a fractionating column between the round-bottomflask and the condenser. ( )

B. Which of the following steps can be used to separate sodiumsulfate from calcium sulfate?

A Dissolving in water - Filtration - Distillation of filtrateB Dissolving in water - Filtration - Evaporation of f iltrateC Dissolving in water - Distillation - Evaporation of

filtrateD Sublimation - Dissolving in water - Evaporation of

filtrate ( )

9. Which of the following steps can be used to obtain a pure

sample of lead(ll) sulfate which is contaminated with somelead(ll) carbonate?

A Dissolving in nitric acid - Filtration - CrystallisationB Dissolving in nitric acid * Filtration - Washing with

waterC Dissolving in water + Filtration - Evaporation of f iltrateD Heating * Dissolving in water - Filtration - Washing

with water ( )

Unit 2 I t*elhads rsl ?uriticcslian end Anolysis IRefer to the following to answer questions 10 and 1 1 .

A desert survival kit often contains a plastic sheet and a cup to be

used for collecting water at times when drinking water is scarce.

Thetechnique involves digging a hole in the ground and securing theplastic sheet over it. A small rock is placed in the middle of the sheetto weigh it down as shown.

rockplastic sheet

ground

small

After a few hours, moisture from the ground collects on the undersideof the sheet, trickles down the sloped sides and drips into the cup.

U 10. Which of the following is the overall process that takes place

to obtain the water in the cup?

A Filtration B Dissolving

C Distillation D Evaporation ( )

\\,g1 1 . A man decided to increase the output of water obtained from

the setup shown by adding suitable liquids to the pit he dug.He considered the following options:

I His own urine

ll Seawater from a nearby beachlll Gasoline from an abandoned jeep

lV Bottle of red wine found in an abandoned backpack

Which liquid(s)will not yield clean, drinkable water for him?

A lll only B I and lll onlyC ll and lV only D l, lll and lV only ( )

U 12. A shisha or hookah is a device used for smoking tobacco. ltinvolves burning tobacco which has been mixed with f lavours

such as honey, molasses or dried fruit in a water pipe andinhaling the flavoured smoke through a long hose.

Which of the following harmful compounds in tobacco smokeare not likely to be removed by the water?

MeltingpoinV'C

BoilingpoinV'G

Solubilityin water

Nicotine -19 247 Soluble

Tar 1 00-200 350-400 lnso luble

Carbon monoxide 205 -1 91 I nsol uble

Phenanthrene 99 340 lnsoluble

A Tar

B Tar and phenanthrene

C Carbon monoxide and nicotineD Tar carbon monoxide and phenanthrene

0

0

0conicalflask

0

0

water droplet

()

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1O Theme 1 I Experimentol Chemistry

13. A mixture of plant pigments and chlorophyll was separated

using chromatography.

The following chromatogram was obtained by spotting a

drop of the concentrated sample at the centre of a piece ofchromatography paper and adding drops of solvent to the spot

to separate out the pigments.

xanthophyll (X) chlorophyll A(chA)

carotene (C)chlorophyll B(chB)

The separation was repeated using the following setup:

filter paper

solvent

Which chromatogram would be observed?

solvent front

C ChBChAxx

ChAChB

CxChAChB

C

Refer to the following to answer questions 15 and 16.

A student wanted t0 investigate the colour additives used in sixdifferent soft drinks 11,2,3,4, 5 and 6)from a specific manufacturerusing paper chromatography. The following chromatogram wasobtar ned.

solvent front

start line

\\,g

M0

R

123456

14. A scientist suspected that some red lentils might be added

with two artificial color additives, X and Y.

He extracted a concentrated sample of liquid from the lentilsusing water and developed the chromatogram to find a single

spot of dye X. He repeated the experiment using ether and

obtained a single spot of Y. He repeated the experiment withethanol and finally managed to identify X and Y in the lentilsample.

What can you conclude about X and Y?

A Y is soluble in water, but X is insoluble.B X is soluble in ethanol, but Y is insoluble.C Y is soluble in water but insoluble in ether.

D X is soluble in ethanol but insoluble in ether. ( )

\\,g 15. Which soft drinks probably contained the same mixture ofcolour additives?

A land4only B 3and6onlyC 1,4and5 D 2,5and6 (

)

\\/g 16. What can we conclude about soft drink 6?

A lt contains three colour additives.B lt is likely to contain three colour additives.C lt contains at least three colour additives.D lt contains at most three colour additives.

Befer to the following t0 answer questions 17 and 1B

The table shows the melting points and boiling points of sixsubstances.

Substance Melting poinV'C Boiling poinU'C

U 99 340

v 0 100

W -11 4 79

x bJ 351

Y -95 57

z BO 218

linespot

AB

ChChxC

A C D

$

$

,

tl

tttl

&-

tF*-

,-FL

L

()

()

IDan

yal E

duca

tion

A mixture containing some of the substances was separated by

fractional distil lation as shown.

thermometer

water out

condenser

fractionatingcolumn

flask coldwater in

conical llask

distillate

granule

The following graph was obtained

Temperature ('C)

20 n 60 80 100 120

Volume of distillate 1ml.y

0

0

0

theat

100

90

80

70

60

500

\V0

\\,0

\V0

17. Which substances are present in the mixture?

A XandY B WandYC U,XandZ D V,WandY

18. When the temperature of the thermometer shows a reading

of 63'C, what is the composition of the mixture in the round-

bottom flask?

A mainly X B mainly WC mainlyUandZ D mainlyVandW (

)

19. An electronic circuit board manufacturer uses three differentorganic solvents - alcohol, mineral spirits solvent and

acetone, for various cleaning applications.

The three different waste streams are:

1. a suspension of silicon primer and dust in alcohol

2. a soluti0n of oil in a mineral spirits solvent

3. a solution of ink in acetone

\VCI

\\,s

\\,0

Unil2 I l*ethoas ol ?;rt{:;atic)n crd Anoiysis 11

Which of the following can be used to help the manufacturerrecover these three solvents at high purity?

A Electrolysis

B ChromatographyC Fractional distillationD Filtration and distillation ( )

20. The diagram shows a chromatogram which was prepared

using spots of four colours, W, X, Y and Z, obtained fromdifferent parts of the body of a toy car.

solvent front

start line

WXYZ

Based on this result, how many different colour additiveswere used in making the four colours?

A4 B 6

c B D 10 ( )

21. Sea salt is salt obtained from the sea and is prized for thevarious trace minerals found in it.

Which of the following is the most energy-efficient methodfor isolating sea salt from seawater and also ensures theretention of the trace minerals?

A Filtration B DistillationC Evaporation D Crystallisation ( )

22. Ihe f ollowing graph shows the temperature changes when a1:1 mixture of methanol (melting point -97"C, boiling point

65"C) and propan-2-ol (melting point -89"C, boiling point

82'C)was distilled.

Temperature ("C)

D

C

A B

20 30 40

Volume of distillate (ml)

85

80

75

70

65

0

t$t,

l0 50

()

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12 Themel I [xperimeniclChemistry

lf aZ-nl fraction of the distillate was collected at each of thepoints A, B, G and D indicated on the graph, which fractionwould contain the highest proportion of methanol?

A Fraction collected at AB Fraction collected at BC Fraction collected at G

D Fraction collected at D ( )

\V/g 23. Which mixture cannot be separated into its components by

adding water, stirring and filtering?

A Sugar and charcoal

B Calcium chloride and iron(lll) oxide

C Aluminium nitrate and potassium sulfateD Potassium carbonate and lead(ll) carbonate ( )

Refer to the following to answer questions 24lo 26.

Vitamins are essential nutrients needed in small amounts for various

roles in the human body. They are either water-soluble or fat-soluble.

A sample of herbal tea, X, containing four water-soluble vitamins,was analysed using chromatography with water as solvent. Whenthe solvent front reached the position indicated, the chromatogramwas placed under ultra-violet light. The following diagram shows thechromatogram obtained.

solvent front

start line

\\,0 24. Why was the chromatogram placed under ultra-violet light?

A To ensure the separation of X is completeB To prevent the volatile vitamins from evaporatingC To reveal the positions of the different spots tn the

chromatogramD To prevent separation of components that will interfere

with the experiment ( )

U 25. Vitamin 8,, has a R, value of 0.34. Which spot belongs to

vitamin B,r?

A Spot A B Spot BC SpotG D SpotD (

)

26. What can be deduced from the results?

A X consists of other water-soluble vitamins.B One of the vitamins in X is not soluble in water.C X is made up of three water-soluble vitamins and one

fat-soluble vitamin.D Allowing the chromatogram to develop over a longer

period of time will improve the separation of the vitaminsinX. (

)

\\,0 27. Glycerin is a compound widely used in the pharmaceutical

industry. lt has a melting point of 18'c, a boiling point of290"C and is soluble in water.

Which diagram shows the method most suitable forseparating glycerin from a mixture of glycerin and water?

mixture

water out

mixture glassbeads

water int

mixture

D

Befer to the following t0 answer questions 28 and29

The following apparatus can be used to convert Nylon-6,6 back toits monomers.

+ water out

condenser

water in -*

theat

BA

00

C

theat

Nylon-6,6+ sulfuric

granules(VI) acid

theat

The reaction mixture of Nylon-6,6 with concentrated sulfuric acid washeated for three hours. The nylon granules were observed to dissolveafter 45 min. At the end of the experiment, the mixture was left tocool and then placed in an ice bath.

6

*

&

I

XABCD

U

Q

()

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M0 28. What is the purpose of the condenser?

A To minimise contact of reaction mixture with airB To allow the monomers to escape as fast as they are

formedC To enable the Nyl0n-6,6 reaction mixture to mix more

eff icientlyD To prevent the monomers from escaping ( )

Unit 2 I b;r*th*ds ot Puriflcotion ond Anolysis 13

32. Heavy water (DrO) is water in which both the hydrogen atomshave been replaced with deuterium, the isotope of hydrogen(,D).

It is found naturally in very small amounts in water, about1 part in 5000 of ordinary water, and is sought after for use

in some nuclear reactors.

0rdinarywater

Heavywater

[\/olecular mass 1B 20

lVelting point/'C 0 3.8

Boiling point/'C 100.0 101 4

Density/g cm 3 0.997 1.104

Which process can be used t0 recover heavy water fromordinary water?

A CrackingB DistillationC Separating funnelD Fractional distillation (

)

33. A gas, Y, was made from a reaction and collected by passing

through a U-tube immersed in an ice mixture. The gas

condensed into a colourless liquid.

Y

colourless liquid

What could be the melting and boiling points of Y?

\V0

Urr. ,n, monomers of Nylon-6,6 obtained from the reaction are

Meltingpoint/'C

BoilingpoinU"G

Hexanedioic acid 1 53"C 338"C

1, 6-diaminohexane 42C 205"C

The 1,6-diaminohexane has formed a soluble saltwith sulfuricacid. What method can be used to separate the monomersobtained from the reaction mixture?

A FiltrationB FractionaldistillationC Use of separating funnelD Dissolve in suitable solvent, filter and crystallise

()

\\,g 30. Which of the following has a fixed melting pointand boilingpoint?

A Terylene B GlucoseC Bronze D Tap water (

)

\\,g 31. Liquation is an old method of separating a metal from its oreand is shown in the following diagram.

metal ore

\\,0

Gas------>

lce

impurities

sloping hearth

purer liquidmetal

Tin ore, containing iron and lead and other impurities, can

be refined t0 a purer form using this method. The impure trn

ore rs added from the top of the f urnace, which has a slopinghearth. The pure liquid tin is collected at the bottom of thefurnace, while the impurities are left behind.

What can you deduce about the properties of tin from themethod?

A lt is an inert metal.

B lt is less reactive than iron and lead.

C lt is more reactive than iron and lead.

D lt has a melting point and boiling point lower than those

of iron and lead. ( )

theat

Melting poinV'C Boiling poinU"C

180 204

B -123 21

C -18 -33

D -81 -84

()

A

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14 Theme I I txperimentol Chemistry

34. A natural colour dye was dissolved in ethanol and itschromatogram (labelled X)developed. ln a second experiment,

the same substance was then spotted on a longer piece ofchromatogram paper and its chromatogram developed using

the same solvent.

solvent

start line

\\,g

\\,s

\\,g

XABCD

Which chromatogram shows the result observed in the second

experiment?

A Chromatogram A B Chromatogram B

C ChromatogramC D ChromatogramD ( )

35. An unknown compound X (melting point of 130 - 131"C) is

mixed with another unknown compound Y (melting point

of 130 - 131'C). The mixture of X and Y is found to melt at127 - 130"C.

What conclusion can be drawn from the result?

A X and Y are pure.

B Either X or Y is impure.

C X and Y are the same compound.

D X and Y are not the same compound. ( )

36. Citric acid (melting point '153'C, boiling point 175'C) is a

white solid used in soft drinks as a flavouring and preservative.

A solution of citric acid in ethanol (melting pornt -114'C,boiling point 78 "C) was gently heated using the apparatus

shown to separate the components of the mixture.

thermometer

flask

solution water out

condenser

anti-bumpinggranule

coldwater in'

conical

disti I late

Which of the following graphs shows the distillation process

above?

theat

0

0

0

a&

A Temperature ('C)

175

B

roomtemperature

room

roomtemperature

room

Volume of distillate (ml)

Temperature ('C)

78

C

Volume of distillate (ml)

Temperature ('C)

175

D

Volume of distillate (ml)

Temperature ('C)

78

\\,0

temperatureVolume of distillate (mI) ( )

37. A student carried out a chromatography of a sample toseparate the amino acids present.

He performed a second chromatography experiment on

the sample. The following shows the two chromatograms

obtai ned.

solvent front

Experiment 1 Experiment 2

Why do the two chromatograms show different results?

A The solvent moved up the paper at different speeds.B Different solvents were used for the two experiments.C The sample for the second experiment was contaminated.D The sample for the second experiment was m0re

concentrated. ( )

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\Vg 38. Which of the following pairs of homogeneous mixtures canbe separated using the following apparatus?

thermometer

flask

solution water out

Unit 2 I t'l'ethrsds r:t ?urif*rslion cnd An*lysis 15

40. A homogeneous liquid mixture was fractionally distilled in

order to separate the liquids present.

thermometer

water out

condenser

column

coldwater in

conical flask

distillate

-bumpinggranule

A temperature-time graph was plotted as shown:

Temperature ('C)EF

Ms

Nl4D4

100

90

80

'70

60

50

4A

30

20

condenser

theat

anti-bumpinggranule

flaskcoldwater in 0

0

0

liquidmixture

conical

distillate

B 0andSD BandS

theat

C DAPCP

and 0and B

\\,0 39. A student attempted t0 extract the oil from sunflower seeds

using a home-made oil press shown below. The sunflowerseeds are f irst crushed and added with water to the oil press

to improve the extraction efficiency.

+

crushedsunflower seeds

ATime (min)

246810

Which of the following method can be used to recover the

sunflower oil from the contents in the beaker?

A Cracking B Filtration

C Fractional distillation D Use of separating funnel()

At which intervals should the liquid fractions have been

col lected?

A AD B BCandDEC GDandEF D AB,GDandEF ( )

Sodium ethanoate (CHrCOONa) is used as a food additive and

also in instant heat pads. A student is considering if wateror cyclohexane can be used t0 separate a mixture of sodium

ethanoate and calcium sulfate.

Which of the following shows the c0rrect sequence of steps

for separating the mixture?

A Dissolving in water - Filtration - Distillation

B Dissolving in water - Filtration - Evaporation

C Dissolving in cyclohexane - Fitration + Distillation

D Dissolving in cyclohexane - Filtration - Evaporation()

,rurr9 Purilv r/ ruililrg lruilrv r

P otr tr1

o 114 304

R -182 -89

S *123 21

)

0

0

(

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16 Theme 1 I [xperimentol Chemistry

Camphor is a white solid isolated from the camphortree and has medicinal properties. lt has a characteristic penetrating smelland has

to be kept in closed containers in a cool place to prevent the crystals from 'disappearing'. lt is very sparingly soluble in water but readilydissolves in ether, an organic solvent.

Glauber's salt is isolated from a mineralore and consists of hydrated sodium sulfate (NarSOo.10H,0).

A sample of camphor was found to be mixed with sand and Glaubers salt.

How may the components in the sample be separated and recovered?

A Heating - Dissolving in water - Filtration - Crystallisation of filtrate

B Dissolving in ether - Filtration -, Crystallisation of filtrate\ Heat residue

n Dissolving in a mixture of ether and water + Filtration * Separating funnel * Crystallisation

D Dissolving in ether * Filtration.. Crystallisation of filtrate\ Dissolving in water + Filtration - Crystallisation

W* ln some countries, the tap water is described as 'hard'

because it contains mainly a high concentration of calcium

and magnesium ions. This poses problems as these ions can

form insoluble mineral deposits on cooking and household

appl iances.

One way of removing these ions on a large scale is by

adding an aqueous mixture of calcium hydroxide and sodium

carbonate to the hard water.

Which of the following methods can be used to separate theresultant calcium and magnesium products?

A FiltrationB DistillationC Evaporation

D Crystallisation ( )

mixture conical

Nr,D44 A sample of table salt was accidentally added to oil in a

beaker.

Which of the following shows the c0rrect sequence of stepsto recover a pure sample of table salt from this mixture?

A Dissolve in water - Distillation - Evaporation

B Filtration - Dissolve residue in water - DistillationC Filtration - Dissolve residue in water - EvaporationD Dissolve in water - Add mixture to separating funnel -Evaporation ( )

Wou Esters can be prepared by reactions of alcohols and carboxylicacids. The yield of these reactions is often Iow. 0ne way ofimproving the yield is to remove the ester formed as thereaction proceeds. This can be done by fractional distillationas shown.

thermometer

water out

condenser

column

flask cold /water in

reaction

heat

anti-bumpinggranule

Which of the following mixtures wlll yield an ester as thedistillate using this method?

0

0

0

t

A Ethyl ethanoate

117',C\

Ethanol

(78'C)Ethanoic acid

(118"C)

B Butyl ethanoate(1 28"C)

Butanol(1 1 7'C)

Ethanoic acid(1 1B'C)

C Ethyl methanoate(54"C)

Ethanol(78"C)

lVethanoic

acid (101"C)

N/ethyl butanoate(1 02.C)

lVethanol(65'C)

Butanoic acid(1 64'C)

()

D

()

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Wou The diagram shows the apparatus used to prepare the esterpropyl ethanoate.

+ cooling waterflow out

condenser

cooling water +flow in

clamp

heating mantle

lab jack

Propanol, ethanoic acid and a small amount of concentratedsulfuric acid are added to the reaction flask and the mixtureis heated for one hour and then c0oled.

Which of the following method will give the best yield of theester from the reaction mixture?

A Filter and recover the ester as the residue.B Carry out fractional distillation on the f inal mixture and

collect the distillate at 102"C.

C Transfer the reaction mixture to a separating funnel andadd water to separate the ester layer.

D Heat the flask containing the reaction mixture tosaturation and cool to crystallise the ester out. ( )

47. Toluene and cyclohexane are two common organic solventsand they form a homogeneous mixture when mixed together.

The following graph shows the boiling points of mixturescontaining different proportions of toluene and cyclohexane.

1

t20

Percent cyclohexane00 80 60 40 20

lt5110

105

100

95

90

85

80

15

70 20 40 60 80

Percent toluene

Unit 2 I l.l,r:1n*dt r:1' ?1t:ri{t;t.:it*r., ;:ir,,4 Ar.,c:t 1sis 17

Which of the following best describes the boiling point of anymixture of toluene and cyclohexane as shown by the graph?

A The boiling point is below that of toluene.B The boiling point is higher than that of cyclohexane.C The boiling point is between that of toluene and

cyclohexane.D The boiling point is below that of both toluene and

cyclohexane. ( )

flask

Wot Gore-tex@ fabric is a type of waterproof and breathablematerial often used in outdoor sportswear lt is able to blockout rainwater and wind while allowing water vapour frombody perspiration to escape. lts structure consists of a fewlayers of porous membranes, each with pores of differents izes.

Which of the following explains how the fabric can be water-resistant and yet breathable?

A The pores in the layers are smaller than liquid waterdroplets 0r water vapour molecules.

B The pores in the layers are bigger than the liquid waterdroplets or water vapour molecules.

C The pores in one layer are smaller than liquid waterdroplets, while the pores in other layers are bigger thanwater vapour molecules.

D The pores in one layer are larger than liquid waterdroplets, while the pores in other layers are smaller thanwater vapour molecules. (

)

49. The diagram shows a chromatogram which was prepared

using spots of four colourings, W, X, Y andZ, obtained fromsweets.

solvent front

start line

WXYZ

How many different distinct colour additives used in making

the four colourings can be deduced from this result?

A3 B 4

c] D e ( )

50. ln an experiment to make vanillin, the compound used in

artificial vanilla flavouring, a white powdery substance Xwas obtained. lt was found to have a melting point of 82"C,

the same as that of vanillin.

To confirm its identity, a mixture of one part X and one part

vanillin was prepared and the melttng point of this mixture

was found to be 71-76'C.

g

w

0

(,

aboc

ag

-

MeltingpoinU'G

BoilingpoinU'C

Solubilityin water

Propyl ethanoate otr 102 Poor

Propanol -121 ol

Ethanoic acid 16 118 Soluble

&&&

100

w

Soluble

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18 Theme I I fxperimentcl Chemisfry

What can be deduced from the result?

A X is vanillin.B X is not vanillin.C X is impure vanillin.D X may contain vanillin.

Befer to the following to answer questions 51 and 52.

1range llis an industrial orange dye commonly used for dyeing of

fabric. A batch of chilli powder was suspected to be contaminated

with )range ll.

A spice importer tested one batch of chilli powder to check that itcontains only safe food colouring. The following shows the results

of the test.

solvent front

ABCDsafe oiange colouring in

food colouring red chilli powder

W,51. Based on the results of the test, what is advisable for the

spice importer to do?

A Reject that batch of chilli powder as it contains the

1range lldye.B Accept that batch of chilli powder as it does not contain

1range ll.

C Accept that batch of chilli powder as it contains mainlysafe orange food colouring.

D Repeatthetestto include lrange llandred chilli powder

colouring. ( )

\\,0 52. The manufactureralso carried outa similarteston a different

batch of chilli powder. The chromatogram obtained is shown

below.

Which one of the safe orange food dye was found in thisbatch?

A DyeA B DyeBC DyeC D DyeD ( )

Thin layer chromatography (TLC) is a type of chromatographysimilar to paper chromatography and uses coated plates

instead of paper for separation. lt can be used to monitor

the progress of a reaction, for example, the conversion ofcompound A to B.

To do this, a sample of the reaction mixture (labelled X) wasspotted together with compounds A and B at the beginning ofthe reaction on a TLC plate and the chromatogram developed.

Simrlar plates were prepared at regular intervals and theirchromatograms developed as shown below:

ABX0 min

ABXl-5 min

ABX30 min

ABX ABX45 min 90 min

What is the optimal reaction time for the conversion of

compound A to B?

A 15 min B 30 min

C 45min D 90min ( )

Refer to the following to answer questions 54 and 55.

1-hexene(CuH,r)and 1-heptene(C,H,o)are two members of the alkene

class of hydrocarbons.

A small amount of a mixture of I -hexene and 1 -heptene was placed

in a boiling tube and gently heated to boiling in a sand bath using

the following setup:

dropper

coppermetal sponge vapour droplets

boiling hexene-heptene

x

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chips mixture

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Vapours were formed and could be seen condensing on the sides ofthe tube. When the vapour condensation line reached the level markedX, the hot vapours were very slowly withdrawn and condensed by

using a small dropper.

\tl4D54. What is the purpose of the copper metal sponge?

A [t/inimises contact of the mixture with airB Prevents the two compounds from escapingC Acts as a catalyst to speed up the reaction of the two

compounds

D Provides large surface area for repeated vaporisation and

condensation ( )

d UU. *nu, process is demonstrated in this experiment?

Wuu

A Cracking

B Combustion

C Addition reactionD Fractional distillation

Liquation is an old method of separating a metal from its oreand is shown in the following diagram.

impure metal ore

iimpurities left behind

sloping hearth

pure metal/concentrate

Tin ore, containing iron and lead and other impurities, can

be refined to a purer form using this method. The impure tinore is added from the top of the furnace, which has a slopinghearth. The pure liquid tin is collected at the bottom of thefurnace, while the impurities are left behind.

Which of the f0llowing statements is not true?

A Tin has a melting point lower than that of its impurities.B Tin can be refined using liquation because it has a low

melting point.

C Little air rs allowed into the furnace to minimise contactof tin with air.

D The f urnace is set at a temperature just below the meltingpoint of tin. (

)

EXTENSION QUESTION

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Unit 2 I Metho<js of Puriflcolion ond Anolysis 19

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