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SCIENCE CHEMISTRY OOOO----LEVEL 2012 LEVEL 2012 LEVEL 2012 LEVEL 2012 QUESTIONS AND SUGGESTED ANSWERSQUESTIONS AND SUGGESTED ANSWERSQUESTIONS AND SUGGESTED ANSWERSQUESTIONS AND SUGGESTED ANSWERS A1. The table gives the laboratory tests for four gases. Complete the table. [3]

gasgasgasgas testtesttesttest resultresultresultresult chlorine insert damp litmus paper bleachespaper bleachespaper bleachespaper bleaches/ turns litmus / turns litmus / turns litmus / turns litmus

whitewhitewhitewhite ammonia insert damp red litmus turns litmus blue

oxygen insert insert insert insert glowing splintglowing splintglowing splintglowing splint bursts into flame sulfur dioxide pass into acidified potassium

dichromate(VI) solution solution turns from solution turns from solution turns from solution turns from orange to orange to orange to orange to

greengreengreengreen [345647 89:;98< =43> 9?@548< A:>B :7C?D< C?8 D7<<? 6:7 EF] A2. Iron will rust. (a) (i) Give two properties of iron. [2]

GH4<3>9:? 898 ?:> 3>C>< @B<=9@C5 :7 IBJ39@C5 I7:I<7>9<3 A4> 3>C>9?D @B<=9@C5 I7:I<7>9<3 93 8<<= 3C6<7 C3 H4<3>9:? B9?><8 K9>B ′743>9?D′ M

Acceptable:Acceptable:Acceptable:Acceptable: ---- it is malleableit is malleableit is malleableit is malleable ---- it is able to conduct electricity in any statit is able to conduct electricity in any statit is able to conduct electricity in any statit is able to conduct electricity in any stateseseses ---- it has high melting and boiling pointit has high melting and boiling pointit has high melting and boiling pointit has high melting and boiling point - it forms coloured compoundsit forms coloured compoundsit forms coloured compoundsit forms coloured compounds ---- it is a good catalytic substanceit is a good catalytic substanceit is a good catalytic substanceit is a good catalytic substance ---- it can be extracted by carbon reductionit can be extracted by carbon reductionit can be extracted by carbon reductionit can be extracted by carbon reduction ---- it produces hydrogen gas when added to acidsit produces hydrogen gas when added to acidsit produces hydrogen gas when added to acidsit produces hydrogen gas when added to acids (ii) Describe how machines made of iron can be prevented from rusting. [1]

By By By By using zinc as galvanising to protect iron.using zinc as galvanising to protect iron.using zinc as galvanising to protect iron.using zinc as galvanising to protect iron. Acceptable:Acceptable:Acceptable:Acceptable: ---- by fully coating the machines with a layer of grease/oil.by fully coating the machines with a layer of grease/oil.by fully coating the machines with a layer of grease/oil.by fully coating the machines with a layer of grease/oil. (b) A student wants to find out what is required for rusting and records the results of

the experiment after some time.

Tube A : iron nails in a sealed tube containing oil and boiled distilled water; no rust

Tube B : iron nails in a sealed tube containing dry air and some drying agent; no rust

Tube C : iron nails in an unsealed tube containing air and water; nails rusted

Tube D : copper nails in an unsealed tube containing air and water; no rust Tube E : iron nails in an unsealed tube containing air and seawater; nails

rusted badly.

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(i) Which tube contained no water? [1]

BBBB

(ii) What do the results of tube C and D show? [1]

Iron, when exposed to air and water, will rust but copper, when exposed to Iron, when exposed to air and water, will rust but copper, when exposed to Iron, when exposed to air and water, will rust but copper, when exposed to Iron, when exposed to air and water, will rust but copper, when exposed to

air and water, does not rust.air and water, does not rust.air and water, does not rust.air and water, does not rust.

GS: =C7T 93 CKC78<8 96 <9>B<7 97:? :7 @:II<7 93 ?:> 8<3@79A<8;CU:98 439?D >B< ><7= :V ;JD<?V6:7 (99) M

(iii) Rust appeared in C. Suggest which substance found in air is required for

rusting to take place? [1]

OxygenOxygenOxygenOxygen

(iv) Machines made of iron if left near the sea rusts more quickly than those left

inland. How do the results of the experiment support the observation? [1]

Tube E, which shows that iron nails when left Tube E, which shows that iron nails when left Tube E, which shows that iron nails when left Tube E, which shows that iron nails when left exposed to air and seawaterexposed to air and seawaterexposed to air and seawaterexposed to air and seawater,,,,

has the has the has the has the mostmostmostmost extensive rusting process.extensive rusting process.extensive rusting process.extensive rusting process.

A3. Use the Periodic Table provided. (a) What is the common name given to elements in: [2]

Group 0 :Group 0 :Group 0 :Group 0 : Noble gasesNoble gasesNoble gasesNoble gases

Group I :Group I :Group I :Group I : Alkali metalsAlkali metalsAlkali metalsAlkali metals

[[CT< ?:><: S: ′C5TC59?< =<>C53′] (b) Answer the questions below using ideas of electronic structures. [3] (i) Why do elements in Group 0 lack chemical reactivity?

The elements have The elements have The elements have The elements have full shell electronic structuresfull shell electronic structuresfull shell electronic structuresfull shell electronic structures and hence and hence and hence and hence do not needdo not needdo not needdo not need

to to to to gain or lose electronsgain or lose electronsgain or lose electronsgain or lose electrons to obtain stable nobleto obtain stable nobleto obtain stable nobleto obtain stable noble----gas configuration.gas configuration.gas configuration.gas configuration.

(ii) Why are chlorine, bromine and iodine found in the same group?

All 3 elements have All 3 elements have All 3 elements have All 3 elements have 7 valence electrons7 valence electrons7 valence electrons7 valence electrons and hence need to and hence need to and hence need to and hence need to gain 1 electrongain 1 electrongain 1 electrongain 1 electron

into their valence into their valence into their valence into their valence shell to obtain shell to obtain shell to obtain shell to obtain stable noblestable noblestable noblestable noble----gas configurationgas configurationgas configurationgas configuration. Thus,. Thus,. Thus,. Thus,

they are all grouped in they are all grouped in they are all grouped in they are all grouped in Group VIIGroup VIIGroup VIIGroup VII....

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(iii) Explain why the elements change from metallic to non-metallic character across the period from lithium to fluorine.

Across the period, the no. oAcross the period, the no. oAcross the period, the no. oAcross the period, the no. of valence electrons in the atoms of element f valence electrons in the atoms of element f valence electrons in the atoms of element f valence electrons in the atoms of element

IncreasesIncreasesIncreasesIncreases. Hence the . Hence the . Hence the . Hence the elements change from tendency of losing valenceelements change from tendency of losing valenceelements change from tendency of losing valenceelements change from tendency of losing valence

electrons to gaining of electrons to form ions, becoming from metallic to electrons to gaining of electrons to form ions, becoming from metallic to electrons to gaining of electrons to form ions, becoming from metallic to electrons to gaining of electrons to form ions, becoming from metallic to

nonnonnonnon----metallic in character.metallic in character.metallic in character.metallic in character.

(c) Give the formula of the compound formed. (i) when an element from Group I reacts with an element from Group VI, [1]

SC]^

[_?J IC979?D 9? >B< 7C>9: :6 ]: E] (ii) when an element from Group II reacts with an element from Group VII. [1]

FD`5] [_?J IC979?D 9? >B< 7C>9: :6 E: ]] A4. The diagram shows the reaction of an organic substance HHHH. (a) Identify FFFF, GGGG, HHHH and JJJJ. [4]

F :F :F :F : glucoseglucoseglucoseglucose

G :G :G :G : carbon dioxidecarbon dioxidecarbon dioxidecarbon dioxide

H :H :H :H : ethanolethanolethanolethanol

J :J :J :J : ethanoic acidethanoic acidethanoic acidethanoic acid [_@@<I> C?3K<73 D9U<? C3 6:7=45C<]

colourless solution

FFFF add yeast and warm

colourless gas GGGG

colourless solution

HHHH

bubble into limewater

white ppt

atmospheric oxidation

colourless solution

JJJJ blue litmus

paper

litmus turns red

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(b) Draw the structural formula of HHHH. [1] [_@@<I> 3>74@>47< :6 d ^e K9>B:4> BJIB<? 9? A<>K<<?] (c) Give the functional group in JJJJ that turns the blue litmus red. [1]

[S: =C7T 6:7 =9339?D BJIB<? :6 @C7A:?] A5. Identify the oxidising agent and the reducing agent. [2] (a) 2ghi j g → 2gh j gil

oxidising agent:oxidising agent:oxidising agent:oxidising agent: CuOCuOCuOCuO

reducing agent:reducing agent:reducing agent:reducing agent: CCCC

Not accepted: copper in copper(II) oxide / copperNot accepted: copper in copper(II) oxide / copperNot accepted: copper in copper(II) oxide / copperNot accepted: copper in copper(II) oxide / copper Accept: chemicalAccept: chemicalAccept: chemicalAccept: chemical name / mole ratio includedname / mole ratio includedname / mole ratio includedname / mole ratio included (b) mn j ghlo → gh j mnlo

A6. (a) At room temperature and pressure, water is a liquid but methane is a gas. (i) Name the type of bonding in these compounds. [1]

Covalent bondsCovalent bondsCovalent bondsCovalent bonds [q: ?:> C@@<I> ′9?>7C=:5<@45C7 6:7@<3′]

(ii) Draw the ‘dot and cross’ diagrams to show the electronic structure of the two

compounds. [4] Water:

Methane:

oxidising agent:oxidising agent:oxidising agent:oxidising agent: `4]o

reducing agent:reducing agent:reducing agent:reducing agent: FeFeFeFe

Key: : electrons of oxygen x : electrons of hydrogen

Key: : electrons of carbon x : electrons of hydrogen

G EF 8<84@><8 6:7 <9>B<7 =9339?D T<J :7/C?8 ?: 6455 <5<@>7:? 3>74@4>7<M

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(b) Magnesium chloride has a higher boiling point than methane. (i) Name the type of bonding for magnesium chloride. [1]

Ionic bondIonic bondIonic bondIonic bond

(ii) Using the concept of bonding, explain the difference in boiling point of

magnesium chloride and methane. [2]

FD`5] is an is an is an is an ionic compoundionic compoundionic compoundionic compound with with with with giant crystal latticegiant crystal latticegiant crystal latticegiant crystal lattice where where where where oppositelyoppositelyoppositelyoppositely----

charged ionscharged ionscharged ionscharged ions arararare held by e held by e held by e held by strong electrostatic forcesstrong electrostatic forcesstrong electrostatic forcesstrong electrostatic forces and and and and huge amount of huge amount of huge amount of huge amount of

energyenergyenergyenergy is required to overcome, thus a is required to overcome, thus a is required to overcome, thus a is required to overcome, thus a highhighhighhigh boiling point. But boiling point. But boiling point. But boiling point. But `eu is a is a is a is a

covalent covalent covalent covalent compcompcompcompoundoundoundound with with with with simple molecular structuresimple molecular structuresimple molecular structuresimple molecular structure where where where where moleculesmoleculesmoleculesmolecules areareareare

held by held by held by held by weak intermolecular forcesweak intermolecular forcesweak intermolecular forcesweak intermolecular forces and only and only and only and only small amount of energy small amount of energy small amount of energy small amount of energy is is is is

required to overcome, hence its required to overcome, hence its required to overcome, hence its required to overcome, hence its lowlowlowlow boiling point.boiling point.boiling point.boiling point.

A7. Some metal carbonate tablets are added in excess to acids of the same volume and

concentration. The reactions are carried out at four different temperatures: KKKK, LLLL, MMMM and NNNN. For each experiment, the volume of gas produced is measured at regular time intervals and the graphs show the results tabulated.

Vol/wxy

time

Vol/wxy

time

Vol/wxy

time

Vol/wxy

time

temperature KKKK temperature LLLL

temperature MMMM temperature NNNN

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(a) Using the letters KKKK, LLLL, MMMM and NNNN, state which temperature (i) was the lowest; [1]

LLLL

(ii) gave the fastest reaction; [1]

MMMM

(iii) showed that the reaction was still proceeding after the range of the graph? [1]

LLLL

(b) The experiment at temperature KKKK: (i) was repeated using acid of the same volume at a much lesser concentration.

Draw in the diagram below the graph you would expect to obtain. [2] [`C7A:?C>< 93 >B< <;@<33 7<CD<?> ] [z<33 3><<I D7C89<?> d EF; {:5. J9<58 =4@B 5:K<7(H? 3>C><8 =4@B 5<33<7) d EF] (ii) was repeated using the same mass of metal carbonate in powder form. Draw

in the diagram below the graph you would expect to obtain. [2] [|><<I<7 D7C89<?> d EF; |C=< U:5 J9<58 d EF]

Vol/wxy

time

original graph of temperature KKKK

Vol/wxy

time

original graph of temperature KKKK

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A8. (a) (i) A solution is made by dissolving 53g of sodium carbonate in water to a volume of 500cm3. Calculate the concentration, in g/dm3, of the solution. [1]

Vol. of solution in dmVol. of solution in dmVol. of solution in dmVol. of solution in dm3333 = = = = ���

E��� = 0.5 dm= 0.5 dm= 0.5 dm= 0.5 dm3333 Concentration of solutionConcentration of solutionConcentration of solutionConcentration of solution = = = = ��

�.� = 106 g/dm= 106 g/dm= 106 g/dm= 106 g/dm3333 (ii) A 2dm3 solution contains 53g of sodium carbonate. Calculate the

concentration, in mol/dm3, of the solution. [1] No. of moles of sodium carbonateNo. of moles of sodium carbonateNo. of moles of sodium carbonateNo. of moles of sodium carbonate = = = = ��D

F7 :6 SC]`^�

= = = = ��E��

= 0.5 mol= 0.5 mol= 0.5 mol= 0.5 mol Concentration of solutionConcentration of solutionConcentration of solutionConcentration of solution = = = = �.�

] = 0.25 mol/dm= 0.25 mol/dm= 0.25 mol/dm= 0.25 mol/dm3333

(b) (i) Write the balanced equation for the reaction between sodium carbonate and hydrochloric acid. State symbols are not required. [2]

SC]`^� j ]e`5 → ]SC`5 j `^] j e]^

(ii) What is the number of moles of sodium carbonate that will react with 4 moles

of hydrochloric acid? [1] From equation,From equation,From equation,From equation,

End of Section A

e`5 :::: SC]`^� ratioratioratioratio 2222 :::: 1111 molesmolesmolesmoles 4mol4mol4mol4mol :::: 2222molmolmolmol

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B9. (a) Briefly describe four characteristic reactions of acids. [4] Ans:Ans:Ans:Ans: Using dilute hydrochloric acid as an example. Hydrogen chloride dissolves in water to Using dilute hydrochloric acid as an example. Hydrogen chloride dissolves in water to Using dilute hydrochloric acid as an example. Hydrogen chloride dissolves in water to Using dilute hydrochloric acid as an example. Hydrogen chloride dissolves in water to

dissociate into dissociate into dissociate into dissociate into eo ions that characterize the following acid reactions:ions that characterize the following acid reactions:ions that characterize the following acid reactions:ions that characterize the following acid reactions: (1)(1)(1)(1) Metal j Acid:Metal j Acid:Metal j Acid:Metal j Acid:

When hydrochloric acid is added to a metal such as magnesium (exclWhen hydrochloric acid is added to a metal such as magnesium (exclWhen hydrochloric acid is added to a metal such as magnesium (exclWhen hydrochloric acid is added to a metal such as magnesium (excluding uding uding uding silver and copper), silver and copper), silver and copper), silver and copper), effervescenceeffervescenceeffervescenceeffervescence of hydrogen gas which when passed over a of hydrogen gas which when passed over a of hydrogen gas which when passed over a of hydrogen gas which when passed over a lighted splintlighted splintlighted splintlighted splint extinguishes the splint with a extinguishes the splint with a extinguishes the splint with a extinguishes the splint with a ‘pop’ sound‘pop’ sound‘pop’ sound‘pop’ sound.... The reaction also The reaction also The reaction also The reaction also produces a salt.produces a salt.produces a salt.produces a salt.

(2)(2)(2)(2) Metal carbonate j Acid:Metal carbonate j Acid:Metal carbonate j Acid:Metal carbonate j Acid:

When hydrochloric acid is added to a metal carbonaWhen hydrochloric acid is added to a metal carbonaWhen hydrochloric acid is added to a metal carbonaWhen hydrochloric acid is added to a metal carbonate such as magnesium te such as magnesium te such as magnesium te such as magnesium carbonatecarbonatecarbonatecarbonate, , , , effervescenceeffervescenceeffervescenceeffervescence of carbon dioxide gas is formed which when bubbled of carbon dioxide gas is formed which when bubbled of carbon dioxide gas is formed which when bubbled of carbon dioxide gas is formed which when bubbled into into into into limewaterlimewaterlimewaterlimewater gives a gives a gives a gives a white precipitatewhite precipitatewhite precipitatewhite precipitate. The reaction also produces a salt and . The reaction also produces a salt and . The reaction also produces a salt and . The reaction also produces a salt and water.water.water.water.

(3)(3)(3)(3) Metal hydroxide (Base) j Acid:Metal hydroxide (Base) j Acid:Metal hydroxide (Base) j Acid:Metal hydroxide (Base) j Acid:

When either a soluble or insolubleWhen either a soluble or insolubleWhen either a soluble or insolubleWhen either a soluble or insoluble base is added to hydrochloric acid, such as base is added to hydrochloric acid, such as base is added to hydrochloric acid, such as base is added to hydrochloric acid, such as aqueous sodium hydroxide, aqueous sodium hydroxide, aqueous sodium hydroxide, aqueous sodium hydroxide, waterwaterwaterwater and a salt is produced.and a salt is produced.and a salt is produced.and a salt is produced.

(4)(4)(4)(4) Metal oxide j Acid:Metal oxide j Acid:Metal oxide j Acid:Metal oxide j Acid:

When metal oxide (both basic or amphoteric) is added to hydrochloric acid, When metal oxide (both basic or amphoteric) is added to hydrochloric acid, When metal oxide (both basic or amphoteric) is added to hydrochloric acid, When metal oxide (both basic or amphoteric) is added to hydrochloric acid, such as magnesium oxide, a salt and such as magnesium oxide, a salt and such as magnesium oxide, a salt and such as magnesium oxide, a salt and waterwaterwaterwater is producedis producedis producedis produced....

(b) Describe how pure sample of silver chloride can be prepared using silver metal. Use

the information below for your preparation: • silver does not react with hydrochloric acid; • silver can react with hot concentrated nitric acid; • all nitrates are soluble in water; • silver chloride is insoluble in water. [4]

Ans:Ans:Ans:Ans: Heat about 25.0cmHeat about 25.0cmHeat about 25.0cmHeat about 25.0cm3333 of concentrated nitric acid in a conical flask. of concentrated nitric acid in a conical flask. of concentrated nitric acid in a conical flask. of concentrated nitric acid in a conical flask.

Once Once Once Once hothothothot, add silver metals , add silver metals , add silver metals , add silver metals in excessin excessin excessin excess to the to the to the to the hot concentrated nitric acidhot concentrated nitric acidhot concentrated nitric acidhot concentrated nitric acid until until until until no more no more no more no more dissolvesdissolvesdissolvesdissolves to to to to completely use up thecompletely use up thecompletely use up thecompletely use up the acidacidacidacid.... Filter the mixtureFilter the mixtureFilter the mixtureFilter the mixture to to to to remove unreacted silverremove unreacted silverremove unreacted silverremove unreacted silver. Add . Add . Add . Add aqueous sodium chlorideaqueous sodium chlorideaqueous sodium chlorideaqueous sodium chloride [C?J �7:4I � =<>C5 @B5:798< C@@<I><8]to the to the to the to the filtratefiltratefiltratefiltrate until until until until no more precipitate no more precipitate no more precipitate no more precipitate formsformsformsforms. . . . Filter the mixtureFilter the mixtureFilter the mixtureFilter the mixture to to to to collect silver chloridecollect silver chloridecollect silver chloridecollect silver chloride as as as as residueresidueresidueresidue.... Rinse crystals with distilled waterRinse crystals with distilled waterRinse crystals with distilled waterRinse crystals with distilled water and and and and dry between filter papersdry between filter papersdry between filter papersdry between filter papers....

GFC7T3 C7< CKC78<8 9? =<79> :6: =<>C5 9? <;@<33 >: C@98 I7<@9I9>C>9:? =<>B:8. _?J :6 >B< =9339?D 7<C@>9:? =CJ @C43< C 5:33 :6 ]=C7T3. M

(c) Write a balanced equation for the reaction between a named metal with a named

acid. State symbols are not required. [2] FD j ]e`5 → FD`5] j e]

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B10. (a) Briefly describe an experiment that shows the order of chemical reactivity of calcium, iron, magnesium and sodium. List these metals in order of decreasing reactivity. [6]

Ans:Ans:Ans:Ans: Regents required:Regents required:Regents required:Regents required: all 4 metals and solutions of all 4 metals and solutions of all 4 metals and solutions of all 4 metals and solutions of nitratenitratenitratenitrate of each metal.of each metal.of each metal.of each metal.

DipDipDipDip a piece of magnesium metal into four separate solutions of the metal nitratesa piece of magnesium metal into four separate solutions of the metal nitratesa piece of magnesium metal into four separate solutions of the metal nitratesa piece of magnesium metal into four separate solutions of the metal nitrates as as as as shown above. The shown above. The shown above. The shown above. The observationsobservationsobservationsobservations to each test tubeto each test tubeto each test tubeto each test tube arararare recorded in the table shown e recorded in the table shown e recorded in the table shown e recorded in the table shown bbbbeeeellllow. ow. ow. ow. Repeat tRepeat tRepeat tRepeat the experimenthe experimenthe experimenthe experiment once each for the metal calcium, iron and sodium with the once each for the metal calcium, iron and sodium with the once each for the metal calcium, iron and sodium with the once each for the metal calcium, iron and sodium with the other variables unchangedother variables unchangedother variables unchangedother variables unchanged....

magnesiummagnesiummagnesiummagnesium calciumcalciumcalciumcalcium ironironironiron ssssodiumodiumodiumodium aaaaq.q.q.q. ccccalcium alcium alcium alcium

nitratenitratenitratenitrate No visible No visible No visible No visible reactionreactionreactionreaction

No visible No visible No visible No visible reactionreactionreactionreaction

No visible No visible No visible No visible reactionreactionreactionreaction Na dissolvesNa dissolvesNa dissolvesNa dissolves

aaaaq.q.q.q. iron(II) iron(II) iron(II) iron(II) nitratenitratenitratenitrate Mg dissolvesMg dissolvesMg dissolvesMg dissolves No visible No visible No visible No visible

reactionreactionreactionreaction No visible No visible No visible No visible reactionreactionreactionreaction Na dissolvesNa dissolvesNa dissolvesNa dissolves

aaaaq.q.q.q. magnesium magnesium magnesium magnesium nitratenitratenitratenitrate

No visible No visible No visible No visible reactionreactionreactionreaction Ca dissolvesCa dissolvesCa dissolvesCa dissolves No visible No visible No visible No visible

reactionreactionreactionreaction Na dissolvesNa dissolvesNa dissolvesNa dissolves

aaaaq.q.q.q. sodisodisodisodium um um um nitratenitratenitratenitrate

No visible No visible No visible No visible reactionreactionreactionreaction

No visible No visible No visible No visible reactionreactionreactionreaction

No visible No visible No visible No visible reactionreactionreactionreaction

No visible No visible No visible No visible reactionreactionreactionreaction

In the experiment, a In the experiment, a In the experiment, a In the experiment, a more reactive metal will displace a less reactive more reactive metal will displace a less reactive more reactive metal will displace a less reactive more reactive metal will displace a less reactive metal from metal from metal from metal from its its its its compound.compound.compound.compound. Hence, if the metal dissolves, the metal Hence, if the metal dissolves, the metal Hence, if the metal dissolves, the metal Hence, if the metal dissolves, the metal is more reactive than the metal as is more reactive than the metal as is more reactive than the metal as is more reactive than the metal as the cationthe cationthe cationthe cation.... Thus, the reactivity of the metals in decreasing order is:Thus, the reactivity of the metals in decreasing order is:Thus, the reactivity of the metals in decreasing order is:Thus, the reactivity of the metals in decreasing order is: ssssodium,odium,odium,odium, calcium, calcium, calcium, calcium, magnesium, magnesium, magnesium, magnesium, ironironironiron

[_@@<I><8: F<>C5 j C@98/KC><7; 3>48<?>3 =43> @5<C75J 8<3@79A< >B< <;I<79=<?>] (b) (i) Bromine is more reactive than iodine and reacts with aqueous potassium

iodide to form potassium bromide. Calculate the mass of iodine that is displaced when a solution containing 10g of potassium iodide is reacted with excess bromine. [3]

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Ans:Ans:Ans:Ans: No. of moles of KINo. of moles of KINo. of moles of KINo. of moles of KI = = = = E�DF7 :6 ��

= = = = E�E��

= = = = 0.0602410.0602410.0602410.060241 molmolmolmol �7] j ]�� → �] j ]��7 From equation,From equation,From equation,From equation, Mass of iodine formedMass of iodine formedMass of iodine formedMass of iodine formed ==== 0.03012 x Mr of 0.03012 x Mr of 0.03012 x Mr of 0.03012 x Mr of �] ==== 0.0.0.0.03012030120301203012 x 254x 254x 254x 254 ==== 7.65057.65057.65057.6505 � 7.65g (3s.f)7.65g (3s.f)7.65g (3s.f)7.65g (3s.f) (b) (ii) What element could be used to displace bromine from aqueous potassium

bromide? [1] Accept:Accept:Accept:Accept: Fluorine or ChlorineFluorine or ChlorineFluorine or ChlorineFluorine or Chlorine B11. (a) (i) Define the term ′�hw�n�� �hx�n�(x��� �hx�n�)′. [2] Accept:Accept:Accept:Accept: It is the It is the It is the It is the ssssumumumum of the of the of the of the number of protons and neutronsnumber of protons and neutronsnumber of protons and neutronsnumber of protons and neutrons in the in the in the in the nucleusnucleusnucleusnucleus of an of an of an of an atom of atom of atom of atom of

an elementan elementan elementan element.... [E=C7T 6:7 :?5J 34= :6 I7:>:?3 C?8 ?<4>7:?3] (ii) Chlorine exists naturally as two chlorine isotopes: g���y� and g���y� . Describe the

similarities and differences in the atomic structure and electronic structure of these two atoms. [5]

Ans:Ans:Ans:Ans: For isotopes are atoms of the same element with same number of protons but For isotopes are atoms of the same element with same number of protons but For isotopes are atoms of the same element with same number of protons but For isotopes are atoms of the same element with same number of protons but

different number of neutrons:different number of neutrons:different number of neutrons:different number of neutrons:

Atomic structureAtomic structureAtomic structureAtomic structure Electronic structureElectronic structureElectronic structureElectronic structure `5E��� `5E��� `5E��� `5E���

similaritiessimilaritiessimilaritiessimilarities Both hBoth hBoth hBoth have:ave:ave:ave:

• 17 protons in the 17 protons in the 17 protons in the 17 protons in the nucleusnucleusnucleusnucleus

• 17 electrons in an atom17 electrons in an atom17 electrons in an atom17 electrons in an atom

Both have:Both have:Both have:Both have: • tttthe he he he same electron structure same electron structure same electron structure same electron structure

of 2,8,7 with 3 electron of 2,8,7 with 3 electron of 2,8,7 with 3 electron of 2,8,7 with 3 electron shells and 7 valence shells and 7 valence shells and 7 valence shells and 7 valence electronselectronselectronselectrons

differencesdifferencesdifferencesdifferences IIIIt t t t contains 18 contains 18 contains 18 contains 18

neneneneutronutronutronutrons in s in s in s in its nucleusits nucleusits nucleusits nucleus

It contains It contains It contains It contains 20 20 20 20 neutrons in neutrons in neutrons in neutrons in its nucleusits nucleusits nucleusits nucleus

TTTThere here here here is no difference in is no difference in is no difference in is no difference in electronic structureelectronic structureelectronic structureelectronic structure

(b) (i) Define �n�����n ���x�w x���. [1] Ans:Ans:Ans:Ans: It is the It is the It is the It is the average mass of an atom of an elementaverage mass of an atom of an elementaverage mass of an atom of an elementaverage mass of an atom of an element as compared to as compared to as compared to as compared to E

E] the mass of a the mass of a the mass of a the mass of a carboncarboncarboncarbon----12 atom12 atom12 atom12 atom....

(ii) Chlorine has a relative atomic mass of 35.5. Explain why the value of the

relative atomic mass of chlorine is not a whole number. [2] Ans:Ans:Ans:Ans: Chlorine exists as Chlorine exists as Chlorine exists as Chlorine exists as two isotopes of two isotopes of two isotopes of two isotopes of different percentage composition by different percentage composition by different percentage composition by different percentage composition by massmassmassmass

with with with with different atomic massdifferent atomic massdifferent atomic massdifferent atomic mass, hence the average mass of the isotopes may not , hence the average mass of the isotopes may not , hence the average mass of the isotopes may not , hence the average mass of the isotopes may not give rise to a whole number.give rise to a whole number.give rise to a whole number.give rise to a whole number.

End of Section B

�� :::: �] ratioratioratioratio 2222 :::: 1111 molesmolesmolesmoles 0.0602410.0602410.0602410.060241 :::: 0.030120.030120.030120.03012molmolmolmol