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1 The figure shows a piece of electric wire.

a) Which metal is the most suitable for making electric wires? (1 mark)Copper (1)

b) Suggest TWO essential properties of that metal which make it suitable for makingelectric wires. (2 marks)Very good conductor of electricity (1)Very ductile (1)

c) Account for the properties mentioned in (b) in terms of metallic bond. (2marks)Copper is a good conductor of electricity because it has mobile electrons. (1)Copper is ductile because when the metal is pulled, the layers of copper ions can slideover each other but are still bound together by the sea of electrons. (1)

d) Explain with equations, if any, what will happen if this wire is put intoi) dilute hydrochloric acid; and (1 mark)

No observable change as copper has a very low reactivity. (1)

ii) silver nitrate solution. (2 marks)The solution turns blue. / Grey deposits form. / The copper wire dissolves. (1)

Cu(s) + 2AgNO 3(aq) Cu(NO 3)2(aq) + 2Ag(s) (1)or Cu(s) + 2Ag +(aq) Cu 2+(aq) + 2Ag(s)

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2 Consider the following metals:aluminium, copper, iron, lead, titanium, zinc

a) For each of the tasks listed below, choose ONE metal which is best to accomplishthe task. Explain your choice in each case.i) Making pipes for hot water (3 marks)

Copper (1) Strong (1) Resists corrosion (1)

ii) Making replacement hip joints (3 marks)Titanium (1)Any two of the following:Light (1) / very strong (1) / resists corrosion (1) / can be easily shaped (1) / biocompatible(1)

b) i) Explain why aluminium does not corrode easily. (2 marks)

When aluminium reacts with oxygen in the air, an even coating of aluminium oxideforms. (1)This oxide layer sticks to the surface of the metal and is impermeable to oxygen andwater. (1)It protects the metal beneath from further attack.

ii) Aluminium is a main material for making aircraft but its strength is relatively low.Suggest how the strength of aluminium can be improved to make it suitable for makingaircraft. (1 mark)Alloying with other metals (1)

c) Suggest TWO factors that affect the price of a metal. (2 marks)Any two of the following:The abundance of the metal in the Earth s crust (1) / the cost of mining its ore (1) / thecost of extracting the metal from its ore (1)

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3 The following table gives the physical properties of a number of metals.Metal Density

(g cm 3)

Meltingpoint ( )

Electricalconductivity

Thermalconductivity

Strength

V 8.96 1 085 very high very high highW 11.4 327 low low low

X 1.74 650 moderate moderate lowY 2.7 660 high high moderateZ 7.86 1 535 moderate low very high

a) Based only on the information in the table, which metal is most suitable for eachof the following applications: Explain your choice in each case.

i) electric wiring in a house; (1 mark)V. It has the highest electrical conductivity. (1)

ii) building a bridge; (1 mark)

Z. It has very high strength. (1)

iii) constructing the frame of an ultralight aircraft; (2 marks)Y. It has moderate strength (1)and low density. (1)

iv) producing saucepans. (1 mark)V. It has the highest thermal conductivity. (1)

b) For each application, suggest ONE other property the chosen metal should haveso that it is suitable for that application. (4 marks)

i) It should be corrosion resistant. (1)ii) It should not rust. (1)iii) The strength of metal Y can be increased by including another substance to form an alloy. (1)iv) Metal V should be cheap / inert. (1)

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4 Aluminium is made by the electrolysis of molten aluminium oxide. The process iscarried out in a steel tank as shown below.

a) Name a material for making the electrodes. (1 mark)Graphite (1)

b) Decide whether electrode X or electrode Y is the positive electrode. (1mark)Electrode X (1)

c) Suggest why cryolite is used in the process. (2 marks)Aluminium oxide has a very high melting point. (1)Addition of cryolite can lower the temperature required for the extraction process. (1)

d) Explain why electrode X have to be replaced regularly. (1 mark)The oxygen evolved reacts with the carbon to form carbon dioxide. (1)

e) Pure aluminium is rarely used for the construction of large objects. Small amountsof other metals are usually mixed with aluminium.Explain in terms of the structure of aluminium. (3 marks)Pure aluminium is relative weak as the layers of ions can easily slide over each other. (1)Adding other metals stops the layers from sliding over each other easily (1)and thus makes aluminium stronger. (1)

f) Suggest why aluminium is more expensive than iron. (1 mark)A large amount of electricity is needed for the extraction of aluminium. This makesaluminium expensive. (1)

g) Production of metals has increased in the last 40 years. However, metals such as

copper and iron have not shown as a large percentage increase as aluminium.Explain why the production of aluminium has outstripped copper and iron. (1 mark)Aluminium products are in greater demand. (1)

h) Knowing that aluminium is highly abundant in the Earth s crust, a studentremarked, r ecycling of used aluminium objects is economically unsound .Do you agree with the student? Explain. (2 marks)

No (1)

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Any one of the following:The extraction of aluminium from its ore requires a great amount of energy. (1) /Aluminium objects do not contain much impurities. The cost for removing the impuritiesis low. (1)

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5 To extract iron from haematite (containing iron(III) oxide), the ore is mixed withcoke and limestone. Then the mixture is added at the top of a blast furnace. Hot air is

blown into the bottom of the furnace.a) Use a chemical equation to describe each of the following chemical changeswhich occur in the blast furnace.

i) The combustion of coke to give carbon dioxide. (1 mark)C(s) + O 2(g) CO 2(g) (1)

ii) The reaction of carbon dioxide with coke to give carbon monoxide. (1 mark)C(s) + CO 2(g) 2CO(g) (1)

iii) The reduction of iron(III) oxide to iron by carbon monoxide. (1 mark)Fe2O3(s) + 3CO(g) 2Fe(l) + 3CO 2(g) (1)

b) 383 g of iron(III) oxide are used in the extraction process. (Relative atomicmasses: O = 16.0, Fe = 55.8)

i) Calculate the theoretical yield of iron. (3 marks) Number of moles of Fe 2O3

=32

32

OFeof massmolarOFeof mass

= 1-molg6.159383g

= 2.40 mol (1)According to the equation, 1 mole of Fe 2O3 produces 2 moles of Fe. number of moles of Fe obtained= 2 x 2.40 mol

= 4.80 mol (1)Theoretical yield of Fe= number of moles of Fe x molar mass of Fe= 4.80 mol x 55.8 g mol 1 = 268 g (1)

ii) Calculate the percentage yield of iron if 228 g of iron were actually obtained. (1 mark)Percentage yield of Fe

=g268g228

x 100%

= 85.1% (1)

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6 Copper can be extracted from copper(II) oxide using carbon using theexperimental set-up shown below.

a) Write a chemical equation for the reaction involved. (1 mark)2CuO(s) + C(s) 2Cu(s) + CO 2(g) (1)

b) Suggest ONE observation of the experiment. (1 mark)A brown powder would be observed. (1)

c) In a certain experiment, 9.54 g of copper(II) oxide were heated with excesscarbon. (Relative atomic masses: O = 16.0, Cu = 63.5)i) Calculate the theoretical yield of copper. (2 marks)

Number of moles of CuO

=CuOof massmolar

CuOof mass

= 1-molg5.79g9.54

= 0.120 mol (1)According to equation, 2 moles of CuO produce 2 moles of Cu.

number of moles of Cu produced= 0.120 molTheoretical yield of Cu= number of moles of Cu x molar mass of Cu= 0.120 mol x 63.5 g mol 1 = 7.62 g (1)

ii) The percentage yield of copper is 82.0%. What is the mass of copper produced? (1 mark)Mass of Cu produced= 7.62 g x 82.0%

= 6.25 g (1)

d) Explain whether carbon can also be used to extract magnesium from magnesiumoxide. (2 marks)

NoThe position of magnesium is high in the reactivity series. / Magnesium oxide is stable. (1)Hence it is difficult to reduce magnesium oxide. (1)

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7 a) For each of the following experiments, state ONE observable change andwrite a chemical equation for the reaction involved.i) Iron is put into dilute hydrochloric acid. (2 marks)Iron dissolves. / Gas bubbles are given off. (1)Fe(s) + 2HCl(aq) FeCl 2(aq) + H 2(g) (1)

ii) Potassium is heated in a Bunsen flame. (2 marks)A lilac flame is observed. / A white smoke is formed. (1)4K(s) + O 2(g) 2K 2O(s) (1)

iii) Lead(II) oxide is heated with carbon powder. (2 marks)The yellow solid turns orange. / A solid with metallic lustre is formed. (1)2PbO(s) + C(s) 2Pb(s) + CO 2(g) (1)

iv) Copper is put into silver nitrate solution. (2 marks)Copper dissolves. / A grey solid deposits. / The solution becomes blue gradually. (1)

Cu(s) + 2AgNO 3(aq) Cu(NO 3)2(aq) + 2Ag(s) (1) b) Explain why there is NO reaction in the following experiments.i) Lead is put into dilute sulphuric acid. (2 marks)Insoluble lead(II) sulphate is formed on the surface of lead. (1)It prevents further reaction. (1)

ii) Calcium oxide is heated with carbon powder. (2 marks)Calcium oxide is very stable. (1)It cannot be reduced by carbon. (1)

iii) Zinc is put into magnesium nitrate solution. (2 marks)Zinc is less reactive than magnesium.(1)Zinc cannot displace magnesium from the solution of a magnesium compound. (1)

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8 The following is a record of observations when a black solid X was tested:Test Observation

1 Heating solid X in a stream ofhydrogen gas

Solid X slowly turned to a reddish brownmetal Y.

2 Heating a mixture of X and zinc

powder

A yellow solid Z was formed, which

turned white on cooling. Metal Y was alsoformed.

a) Test 1 could be carried out using the set-up shown below.

i) Suggest ONE way to show that a metal was formed in this test. (1 mark)The solid obtained is a good conductor of electricity. (1)

ii) Suggest why it was necessary to burn the residual hydrogen in the set-up. (1mark)Hydrogen is explosive / flammable. (1)

b) Consider Test 2.i) Suggest what solid Z might be. (1 mark)Zinc oxide (1)

ii) Predict whether metal Y or zinc was discovered earlier. Explain your answer. (2 marks)Metal Y was discovered earlier. (1)Zinc is more reactive than metal Y and hence more difficult to extract. (1)

c) i) Suggest what solid X might be. (1 mark)Copper(II) oxide (1)

ii) Write a chemical equation for the reaction of solid X with hydrogen. (1mark)CuO(s) + H 2(g) Cu(s) + H 2O(l) (1)

d) In an experiment, a piece of zinc was added to a solution of sulphate of Y.i) State TWO expected observations. (2 marks)The zinc metal was coated with a brown layer. (1)The blue colour of the solution faded. (1)

ii) Write an ionic equation for the reaction involved. (1 mark)Zn(s) + Cu 2+(aq) Zn 2+(aq) + Cu(s) (1)

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9 The following metals are arranged in the order of decreasing reactivity.metal a > metal b > metal c > iron > metal d > metal e > metal f

Based on the information given above, answer the following questions.a) Which metal is most likely to tarnish rapidly in air? Explain your answer. (2marks)

Metal a (1)Because it is the most reactive metal and thus reacts rapidly with oxygen in air to form anoxide layer on the metal surface. (1)

b) Which metal is most likely to be found free in nature? Explain your answer. (2 marks)Metal f (1)Because it is the least reactive metal and thus does not form stable compounds readily. (1)

c) Would you expect metal d to react with cold water? Explain your answer. (2

marks) No. (1)Iron has no reaction with cold water and metal d is less reactive than iron. (1)

d) Suggest how metal a can be extracted from its ore. (1 mark)Electrolysis of its molten ore (1)

e) What would be formed when the oxide of metal d is heated with metal b? Explainyour answer. (2 marks)Metal d is formed. (1)Metal b is more reactive than metal d .It can remove oxygen from the oxide of d . (1)

f) Suggest an experiment to show that metal b is more reactive than iron. (2marks)Add metal b to iron(II) sulphate solution. (1)Metal b can displace iron from iron(II) sulphate solution. (1)

g) Can we store the solution of nitrate of metal c in a container made of metal d ?Explain your answer. (2 marks)Yes. (1)Since metal d is less reactive than metal c, no displacement reaction occurs. (1)

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10 X, Y and Z are three different metals. The table below lists the results of threeexperiments carried out using the metals or their oxides.

Experiment X Y ZAdding metal tocold water

no observablechange

no observablechange

formation of acolourless gas

Adding metal tosilver nitratesolution

formation of a greysolid no observablechange formation of acolourless gas and agrey solid

Heating the metaloxide

no observablechange

formation of a solidwith metallic lustre

no observablechange

a) What is the colourless gas formed when Z is added to cold water? Suggest a testfor the gas. (2 marks)Hydrogen (1)It gives a pop sound when tested with a burning splint. (1)

b) Arrange the three metals in order of increasing reactivity. Explain your answer. (3 marks)Y < X < Z (1)X is more reactive than Y as it can displace silver from silver nitrate solution but Ycannot. (1)Z is more reactive than X as it can react with cold water but X cannot. (1)

c) Why is a colourless gas formed when Z is added to silver nitrate solution? (1mark)Z reacts with water in the silver nitrate solution and a colourless gas (hydrogen) is formed. (1)

d) X burns in air with a very bright light. A white powder is formed.i) Suggest what X might be. (1 mark)Magnesium (1)

ii) Write an ionic equation for the reaction between X and silver nitrate solution. (1 mark)Mg(s) + 2Ag +(aq) Mg 2+(aq) + 2Ag(s) (1)

iii) Suggest how X can be extracted from its ore. (1 mark)By electrolysis (1)

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11 A student performs several experiments to determine the order of reactivity offour metals. The results are shown in the table below.

ExperimentMetal

W X Y ZReaction with

cold water

reacts readily no observable

change

no observable

change

reacts

vigorouslyReaction withsteam

reacts readily no observablechange

reacts veryslowly

reactsvigorously

Reaction withdilutehydrochloricacid

reacts readily reacts veryslowly

reacts slowly very dangerous NEVERattempt

Heating themetal oxidewith carbon

no observablechange

formation of asolid withmetallic lustre

formation of asolid withmetallic lustre

no observablechange

a) Arrange the metals in order of reactivity, starting with the most reactive one.Explain your answer briefly. (4 marks)Z > W > Y > X (1)Metals W and Z are more reactive than metals X and Y as W and Z can react with coldwater but X and Y cannot. (1)Metal Z is more reactive than metal W as it reacts more vigorously with water. (1)Metal Y is more reactive than metal X as it reacts slowly with steam but X shows noobservable change. (1)

b) Metal W gives a brick-red flame in flame test.i) Suggest what metal W might be. (1 mark)

Calcium (1)

ii) Write a chemical equation for the reaction between W and water. (1 mark)Ca(s) + 2H 2O(l) Ca(OH) 2(s) + H 2(g) (1)

iii) Draw a labelled diagram of the set-up for carrying out the reaction between Wand cold water, with the collection of the gaseous product. (2 marks)

(1 mark for correct set-up; 1 mark for correct labels; 0 mark if the set-up is not workable.) (2)

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c) The following table lists the year of discovery of the four metals.Metal Year of discoveryW 1808X ancientY ancient

Z 1801Suggest a relationship between the reactivity and the year of discovery of metals. (1mark)Less reactive metals were discovered first and more reactive metals were discovered later. (1)

d) Consider the oxide of metal X, XO. Complete reduction of 123 g of this oxide byhydrogen gas produces metal X and 9.90 g of water. Calculate the relative atomic mass ofX. (Relative atomic masses: H = 1.0, O = 16.0) (3 marks)XO(s) + H 2(g) X(s) + H 2O(l)Let m be the relative atomic mass of X.

Number of moles of H 2O formed=

OHof massmolarOHof mass

2

2

= 1-molg0.18g9.90

= 0.550 mol (1)According to the equation, 1 mole of XO gives 1 mole of H 2O upon reduction. number of moles of XO reduced= 0.550 molMass of XO reduced

= number of moles of XO x molar mass of XO= 0.550 mol x ( m + 16.0) g mol 1 (1)= 123 gm = 208 (1)

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12 The results of a series of displacement reactions are given in the table below.

Salt solution

MetalNitrate of X Lead(II)

nitrateIron(II)nitrate

Silver nitrate

X reaction occurs reaction occurs reaction occursLead no observable

change no observable

changereaction occurs

Iron no observablechange

reaction occurs reaction occurs

Silver no observablechange

no observablechange

no observablechange

a) What is a displacement reaction? (1 mark)The reaction in which a more reactive metal displaces a less reactive metal from a solution of the compound of the less reactive metal. (1)

b) List TWO observable changes when X is put into iron(II) nitrate solution. (2marks)Any two of the following:Metal X dissolves. (1) / A grey solid deposits. (1) / The green colour of the solution fades.(1)

c) Based on the information given above, arrange the metals in descending order ofreactivity. Briefly explain your answer. (4 marks)X > iron > lead > silver (1)X is the most reactive since it can displace all other three metals from solutions of theirsalts. (1)Iron is more reactive than lead and silver because it can displace lead and silver fromsolutions of their salts. (1)Silver is the least reactive as it cannot displace any metal. (1)

d) Chromium should be placed between X and iron in the reactivity series. Supposeyou are provided with chromium(III) nitrate solution, describe an experiment to show this. (2 marks)Put X and iron into two separate test tubes each containing chromium(III) nitrate solution. (1)X can displace chromium from chromium(III) nitrate solution but iron cannot. (1)It shows that chromium is between X and iron in the reactivity series.

e) Write an ionic equation for the reaction between iron and silver nitrate solution. (1 mark)Fe(s) + 2Ag +(aq) Fe 2+(aq) + 2Ag(s) (1)

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13 The reactivity of metals can be determined by the reaction between metal and acid.Five different metals, calcium, tin, zinc, copper and nickel are added to dilutehydrochloric acid respectively. The gas produced is collected by displacement of water.The height of gas collected in the first 30 seconds in each case is measured.

The results are shown in the following table.

Metal Height (cm) of gas collected in the first30 seconds

Calcium 5.5Tin 1Zinc 4.5

Copper 0 Nickel 2.5

a) Write a chemical equation for the reaction between zinc and dilute hydrochloricacid. (1 mark)Zn(s) + 2HCl(aq) ZnCl 2(aq) + H 2(g) (1)

b) Suggest a test for the gas evolved. (1 mark)Hydrogen gas gives a pop sound when tested with a burning splint. (1)

c) Determine the reactivity series in descending order from the results provided. (1 mark)Calcium > zinc > nickel > tin > copper (1)

d) Explain why the reactivity of sodium CANNOT be determined by this method.(1 mark)

Sodium reacts with dilute hydrochloric acid explosively. (1)

e) Explain why it is NOT suitable to use dilute sulphuric acid to replace dilutehydrochloric acid in this experiment. (2 marks)When calcium reacts with dilute sulphuric acid, insoluble calcium sulphate will form onthe surface of calcium. (1)This prevents the metal from further reaction. (1)

f) Another metal was tested and the result was as follows:

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Metal Height (cm) of gas collectedin the first 30 seconds

X 5

i) From the result obtained, rewrite the reactivity series. (1 mark)

Calcium > metal X > zinc > nickel > tin > copper (1)

ii) Suggest what metal X might be. (1 mark)Magnesium / aluminium (1)

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14 a) In 67.5 g of hydrated aluminium sulphate Al 2(SO 4)3 6H 2O, calculate(Relative atomic masses: H = 1.0, O = 16.0, Al = 27.0, S = 32.1; Avogadro constant =6.02 x 10 23 mol 1)i) the number of moles of aluminium ions present; (2 marks)

Number of moles of Al 2(SO 4)3 6H2O

=OH6)(SOAlof massmolar

OH6)(SOAlof mass2342

2342

= 1-molg3.450g67.5

= 0.150 mol (1) Number of moles of aluminium ions = 2 x 0.150 mol = 0.300 mol (1)

ii) the number of moles of water molecules present; (1 mark) Number of moles of water molecules = 6 x 0.150 mol = 0.900 mol (1)

iii) the number of sulphur atoms present; (1 mark) Number of sulphur atoms= 3 x 0.150 mol x 6.02 x 10 23 mol 1 = 2.71 x 10 23 (1)

iv) the number of oxygen atoms present; and (1 mark) Number of oxygen atoms= 18 x 0.150 mol x 6.02 x 10 23 mol 1 = 1.63 x 10 24 (1)

v) the number of ions present. (1 mark)

Number of ions= 5 x 0.150 mol x 6.02 x 10 23 mol 1 = 4.52 x 10 23 (1)

b) A hydrated carbonate (M 2CO 3 10H 2O) is found to contain 62.9% by mass ofwater of crystallization. Calculate the relative atomic mass of the metal M. (Relativeatomic masses: H = 1.0, C = 12.0, O = 16.0) (2 marks)Let m be the relative atomic mass of M.Formula mass of M 2CO 3 10H 2O= 2 x m + 12.0 + 3 x 16.0 + 10 x (2 x 1.0 + 16.0)= 2m + 240.0

Percentage by mass of water in M 2CO 3 10H 2O

=0.2402

0.180m

x 100%

0.2402

0.180m

x 100% = 62.9% (1)

m = 23.0 (1) the relative atomic mass of M is 23.0.

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15 The set-up shown below was used to collect the liquid given off when hydratedzinc nitrate was heated strongly for some time.

a) Explain why tube A was clamped in a slanting position. (1 mark)To prevent the condensed water from running back to the tube and crack the hot glass. (1)

b) Suggest a test to show that the liquid collected in tube B was water.(2 marks)The liquid turns dry cobalt(II) chloride paper (1)from blue to pink. (1)

c) Why is it desirable to keep the free end of the delivery tube above the liquidcollected in tube B? (1 mark)To prevent sucking back of the liquid. (1)

d) The chemical formula of hydrated zinc nitrate is Zn(NO 3)2 nH2O. In the aboveexperiment, 15.0 g of the nitrate produced 6.48 g of water. Calculate the value of n.(Relative atomic masses: H = 1.0, N = 14.0, O = 16.0, Zn = 65.4) (2 marks)Formula mass of Zn(NO 3)2 nH2O= (65.4 + 2 x 14.0 + 6 x 16.0) + n(2 x 1.0 + 16.0)= 189.4 + 18 n 1 mole of Zn(NO 3)2 nH2O contains n moles of H 2O.i.e. (189.4 + 18 n) g of Zn(NO 3)2 nH2O contain 18 n g of H 2O.15.0 g of Zn(NO 3)2 nH2O contain 6.48 g of H 2O.

g0.15g48.6

g)184.189(g18

n

n

(1)

n = 8 (1)

e) When anhydrous zinc nitrate was heated strongly, it decomposed according to the

following word equation:zinc nitrate zinc oxide + nitrogen dioxide + oxygeni) Transcribe the above word equation into a chemical equation. (1 mark)2Zn(NO 3)2(s) 2ZnO(s) + 4NO 2(g) + O 2(g) (1)

ii) What is the colour of zinc oxide when cold? (1 mark)White (1)

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iii) Calculate the mass of oxygen formed from decomposing 22.7 g of anhydrous zincnitrate. (Relative atomic masses: N = 14.0, O = 16.0, Zn = 65.4) (3 marks)

Number of moles of Zn(NO 3)2

=23

23

)Zn(NOof massmolar)Zn(NOof mass

= 1-molg4.189g722.

= 0.120 mol (1)According to the equation, 2 moles of Zn(NO 3)2 gives 1 mole of O 2 upon decomposition.

number of moles of O 2 formed =2120.0 mol = 0.0600 mol (1)

Mass of O 2 formed= number of moles of O 2 x molar mass of O 2 = 0.0600 mol x 32.0 g mol -1 = 1.92 g (1)

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16 In a highly pressurized steam boiler, the oxygen dissolved in water can causecorrosion to the metallic parts of the boiler. The dissolved oxygen can be removed byadding compound X into the boiler.a) Compound X consists of nitrogen and hydrogen only. It relative molecular massis 32.0. The compound contains 87.5% of nitrogen by mass.

i) Deduce the molecular formula of compound X. (Relative atomic masses: H = 1.0, N = 14.0) (3 marks)

Suppose we have 100 g of compound X, containing 87.5 g of nitrogen and 12.5 g of hydrogen.

Nitrogen Hydrogen Number of moles of atomsthat combine mol25.6molg0.14

g5.871-

mol5.12molg0.1

g5.121-

(1)

Mole ratio of atoms1

mol25.6mol25.6

2mol25.6mol12.5

(1)

the empirical formula of compound X is NH 2.

Let (NH 2)n be the molecular formula of compound X.Relative molecular mass of X= n(14.0 + 2 x 1.0)= 16 n 16n = 32.0n = 2 the molecular formula of compound X is N 2H4. (1)

ii) Draw an electron diagram of compound X, showing electrons in the outermost shells only. (1 mark)

(1)

b) The reaction between compound X and oxygen can be represented by thefollowing word equation:X + oxygen nitrogen + waterTranscribe the word equation into a chemical equation. (1 mark)

N2H4 + O 2 N2 + 2H 2O (1)

c) A water sample contains 400 g of dissolved oxygen. Calculate the mass of Xrequired to remove all the oxygen in the sample. (Relative atomic mass: O = 16.0) (2marks)

Number of moles of O 2 in sample

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=2

2

Oof massmolarOof mass

= 1-molg0.162g400

= 12.5 mol (1)According to the equation, 1 mole of X is required to remove 1 mole of O 2. number of moles of X required = 12.5 molMass of X required= number of moles of X x molar mass of X= 12.5 mol x 32.0 g mol -1 = 400 g (1)

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17 A student used the set-up shown below to determine the empirical formula of anoxide of lead.

Town gas (main constituents being carbon monoxide and hydrogen) was passed over theoxide. The oxide was reduced to lead in the experiment. Heating was stopped after sometime. Town gas was still passed through while the combustion tube cooled down. Thefollowing results were obtained.

Mass of combustion tube = 26.91 gMass of combustion tube and contents before heating = 28.98 gMass of combustion tube and contents after heating = 28.70 g

a) Why was town gas passed through while the combustion tube cooled down? (1 mark)To prevent the oxidation of lead by air again. (1)

b) During the experiment, the student heated, cooled and weighed the contents of thetube until the mass remained constant.Explain this action of the student. (2 marks)To ensure that the conversion into lead is complete. (2)

c) Determine the empirical formula of the lead oxide. (2 marks) (Relativeatomic masses: O = 16.0, Pb = 207.2)Mass of lead in the oxide= (28.70 26.91) g= 1.79 g

Mass of oxygen in the oxide= (28.98 28.70) g= 0.28 g

Number of moles of atomsthat combine mol00864.0

molg2.207

g79.11-

mol0175.0

molg0.16

g.2801-

(1)Mole ratio of atoms

00.1mol00864.0mol.008640

03.2mol00864.0

mol0.0175(1)

the empirical formula of the lead oxide is PbO 2.

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d) Write chemical equations to account for the chemical changes of the lead oxide.(2 marks)

PbO 2(s) + 2CO(g) Pb(s) + 2CO 2(g) (1)PbO 2(s) + 2H 2(g) Pb(s) + 2H 2O(l) (1)

e) List TWO potential hazards of this experiment. (2 marks)Town gas is toxic (due to carbon monoxide) and (1)explosive / flammable (due to hydrogen). (1)

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18 A solid sample contains iron and copper only. The composition of the solidsample was analyzed using the following steps:

Step 1 3.00 g of the solid sample was weighed.Step 2 The solid sample was added to excess dilute sulphuric acid.Step 3 Upon completion of reaction, the solid remaining in the mixture was

separated out.Step 4 The solid obtained was washed with distilled water and then dried.

a) Write a chemical equation for the reaction involved in Step 2 . (1 mark)Fe(s) + H 2SO 4(aq) FeSO 4(aq) + H 2(g) (1)

b) Write an ionic equation for the reaction involved in Step 2 . (1 mark)Fe(s) + 2H +(aq) Fe 2+(aq) + H 2(g) (1)

c) Suggest how one could know that the reaction had been completed in Step 3 . (1 mark)

No more gas evolved. (1)d) For Step 3 , suggest how the solid can be separated out from the mixture. (1mark)Filtration (1)

e) Why was the solid obtained washed with distilled water in Step 4 ? (1 mark)To wash away any acid adhering to the residue. (1)

f) For Step 4 , explain why the solid should NOT be dried using a Bunsen flame. (1 mark)The copper will become copper(II) oxide. (1)

g) The mass of the solid obtained in Step 4 was 1.95 g. What is the percentage bymass of iron in the solid sample? (2 marks)Percentage by mass of iron in the sample

=g00.3

g)95.100.3( x 100% (1)

= 35.0% (1)

h) i) Suggest ONE use of copper. (1 mark)Making electric wires / cooking utensils (1)

ii) List TWO properties of copper that make it suitable for the use suggested in (i). (2 marks)Making electric wiresAny two of the following:very good conductor of electricity (1) / very ductile (1) / resists corrosion (1)ORMaking cooking utensils

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Any two of the following:very good conductor of heat (1) / very malleable (1) / strong (1) / resists corrosion (1) /non-poisonous (1)

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19 Potassium is obtained from the ore carnallite. The main metallic compound in theore is hydrated potassium magnesium chloride (KCl MgCl 2 6H 2O). An experiment iscarried out to determine the percentage by mass of hydrated potassium magnesiumchloride in a sample of carnallite.

Step 1 Dissolve 6.17 g of the sample in water.

Step 2 Add excess silver nitrate solution to the solution obtained in Step 1 .Step 3 Separate the silver chloride precipitate formed from the mixture.Step 4 Wash and dry the precipitate. 8.61 g of precipitate are obtained.

(Relative atomic masses: H = 1.0, O = 16.0, Mg = 24.3, Cl = 35.5, K = 39.1, Ag = 107.9)a) i) Silver ion and chloride ion react to give silver chloride according to thefollowing equation:Ag+(x) + Cl (y) AgCl(z)Give the state symbols represented by x, y and z in the equation. (1 mark)x : aq, y : aq, z : s. (1)

ii) Explain why excess silver nitrate solution is used in Step 2 . (1 mark)To react with all the chloride ions. (1)

iii) Draw a labelled diagram of the experimental set-up for separating the silverchloride precipitate from the mixture in Step 3 . (3 marks)

(1 mark for correct set-up; 1 mark for labelling filter funnel and filter paper; 1 mark forlabelling residue and filtrate; 0 mark if the set-up is not workable) (3)

iv) Calculate the number of moles of silver chloride obtained in the experiment. (1 mark)

Number of moles of AgCl

=AgClof massmolar

AgClof mass

= 1-molg4.143g8.61

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= 0.0600 mol (1)

v) Calculate the percentage by mass of KCl MgCl 2 6H 2O in the sample. (3 marks)1 mole of KCl MgCl 2 6H2O contains 3 moles of chloride ions.1 mole of KCl MgCl 2 6H 2O gives 3 moles of AgCl when reacted with excess

AgNO 3(aq). number of moles of KCl MgCl 2 6H 2O in the sample

=3

0600.0 mol

= 0.0200 mol (1)

Molar mass of KCl MgCl 2 6H2O= [39.1 + 24.3 + 3 x 35.5 + 6 x (2 x 1.0 + 16.0)] g mol 1 = 277.9 g mol 1 Mass of KCl MgCl 2 6H 2O in the sample

= number of moles of KCl MgCl 2 6H 2O x molar mass of KCl MgCl 2 6H 2O= 0.0200 mol x 277.9 g mol 1 = 5.56 g (1)

Percentage by mass of KCl MgCl 2 6H 2O in the sample

=g17.6g56.5

x 100%

= 90.1% (1)

b) Suggest how potassium is extracted from carnallite. (1 mark)Electrolysis of molten carnallite (1)

c) In another experiment, potassium is heated in the air.i) Describe the observable changes of the experiment. (2 marks)Potassium burns vigorously with a lilac flame. (1)A white smoke forms. (1)

ii) Write a chemical equation for the reaction involved. (1 mark)4K(s) + O 2(g) 2K 2O(s) (1)

iii) Suggest how potassium should be stored in the laboratory. (1 mark)Store it in paraffin oil. (1)

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20 Agricultural lime is manufactured from limestone by first heating the rock to ahigh temperature in a lime kiln. The product is allowed to cool and a calculated amountof water is added. A white powder called s laked lime is produced.a) Write chemical equations for these TWO reactions. (2 marks)CaCO 3(s) CaO(s) + CO 2(g) (1)

CaO(s) + H 2O(l) Ca(OH) 2(s) (1)

b) Suggest ONE use of slaked lime in agriculture. (1 mark)To neutralize acidic soils. (1)

c) The mineral dolomite is a double carbonate of magnesium and calcium, with thechemical formula CaMg(CO 3)2. An experiment was carried out to determine the

percentage by mass of carbonate in a sample of dolomite using the set-up shown below.

i) Write a chemical equation for the reaction involved. (1 mark)CaMg(CO 3)2(s) + 4HCl(aq) CaCl 2(aq) + MgCl 2(aq) + 2CO 2(g) + 2H 2O(l) (1)

ii) The mass of the sample used was 1.20 g. At the end of the experiment, 0.450 g ofcarbon dioxide was collected.Calculate(1) the number of moles of carbon dioxide collected; and(2) the percentage purity of the dolomite sample. (3 marks)(Relative atomic masses: C = 12.0, O = 16.0, Mg = 24.3, Ca = 40.1)

Number of moles of CO 2 given off

=2

2

COof massmolarCOof mass

= 1-molg0.44g0.450

= 0.0102 mol (1)

According to the equation, 1 mole of CaMg(CO 3)2 reacts with excess acid to give 2 moles of CO 2. number of moles of CaMg(CO 3)2 reacted

=2

0102.0 mol

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= 0.00510 mol

Molar mass of CaMg(CO 3)2 = [40.1 + 24.3 + 2 x (12.0 + 3 x 16.0)] g mol -1 = 184.4 g mol -1

Mass of CaMg(CO 3)2 reacted= number of moles of CaMg(CO 3)2 x molar mass of CaMg(CO 3)2 = 0.00510 mol x 184.4 g mol -1 = 0.940 g (1)

Percentage purity of the dolomite sample

=g20.1g940.0

x 100%

= 78.3% (1)

iii) Assuming that there was no leakage of gas in the set-up, suggest ONE source oferror in the experiment. (1 mark)Some carbon dioxide dissolve in the acid. (1)

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21 a)

The above figure shows the location of a factory which extracts zinc from its ore, zinc blende (ZnS). The flow diagram below shows how zinc is extracted in the factory.

In Stage I , the ore is heated strongly in air. A yellow compound X which becomes whitewhen cold is formed. Besides, an acidic gas Y is evolved and this is emitted to thesurroundings from chimneys.i) (1) Write a chemical equation for the reaction occurred in Stage I . (1mark)2ZnS(s) + 3O2(g) 2ZnO(s) + 2SO2(g) (1)

(2) Name compound X and gas Y. (2 marks)X: zinc oxide (1)Y: sulphur dioxide (1)

ii) In Stage II , X is heated strongly with a black powder.(1) Identify the black powder. (1 mark)Carbon (1)

(2) Write a chemical equation for the reaction occurred in Stage II . (1 mark)2ZnO(s) + C(s) 2Zn(s) + CO 2(g) (1)

iii) State ONE use of zinc. (1 mark)Making galvanized iron / casings of dry cells (1)

b) Statues A and B are mainly made of iron. It is found that statue A rusts morequickly than B.i) Give a reason for this. (2 marks)Wind brings the acidic sulphur dioxide gas to statue A but not B. (1)Acidic gas speeds up the rusting of iron. (1)

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ii) Suggest ONE method to slow down the corrosion of the statues. (1 mark)Plating a metal layer on the statues (1)

iii) Some green patches appear on the statues. Besides iron, suggest another metal thestatues may contain. (1 mark)

Copper (1)

c) Zinc reacts with dilute hydrochloric acid to give hydrogen. (Relative atomicmasses: H = 1.0, Cl = 35.5, Zn = 65.4)i) Write a chemical equation for the reaction involved. (1 mark)Zn(s) + 2HCl(aq) ZnCl 2(aq) + H 2(g) (1)

ii) A sample of hydrochloric acid containing 2.92 g of HCl is added to 3.27 g of zinc.Calculate the mass of hydrogen produced. (4 marks)

Number of moles of HCl used

= HClof massmolar HClof mass

= 1-molg6.35g2.92

= 0.0800 mol (1) Number of moles of Zn used

=Znof massmolar

Znof mass

= 1-molg4.65g3.27

= 0.0500 mol (1)According to the equation, 1 mole of Zn reacts with 2 moles of HCl. Hence 0.0800 moleof HCl reacts with 0.0400 mole of Zn. Therefore Zn is in excess. (1) number of moles of H 2 produced

=2

0800.0mol

= 0.0400 molMass of H 2 produced= number of moles of H 2 x molar mass of H 2 = 0.0400 mol x 2.0 g mol -1 = 0.0800 g (1)

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22 Explain each of the following:a) Aluminium does NOT react with steam unless when the aluminium is washedwith mercury(II) chloride solution. (2 marks)A layer of aluminium oxide is attached to the surface of aluminium and this prevents the reaction of aluminium. (1)

Mercury(II) chloride solution can remove this oxide layer and allow the aluminium underneath to react. (1)

b) Silver nitrate solution CANNOT be kept in an iron bucket. (2 marks)There is a displacement reaction between silver nitrate solution and iron. (1)This will cause the iron to dissolve. (1)

c) Aluminium, rather than copper, is used in making overhead power cables. (1mark)Aluminium is lighter than copper. (1)

d) When calcium reacts with dilute sulphuric acid, gas bubbles are given off for ashort while and then stop. (2 marks)Insoluble calcium sulphate forms in the reaction. (1)It covers the calcium metal and prevents further reaction. (1)

e) Zinc can be extracted from its molten ore by electrolysis. Yet in practice, it isusually extracted by heating its oxide with coke. (1 mark)Electrolysis is an expensive extraction method. (1)

f) It is NOT advisable to buy a can of food if there are scratches on the iron body ofthe can. (2 marks)When the tin coating of a food can is damaged, the iron rusts more quickly than when it is alone (1)

because tin is less reactive than iron. (1)

g) Galvanized iron is NOT used in making food cans. (1 mark)Zinc ions are poisonous. (1)

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23 An iron nail is placed in a gel containing a rust indicator, a mixture of potassiumhexacyanoferrate(III) and phenolphthalein. Blue and pink colours develop around theiron nail after two days.

a) What is the chemical nature of rust? (1 mark)Hydrated iron(III) oxide (1)

b) State the essential conditions for the rusting of iron. (1 mark)Oxygen (0.5) and water (0.5)

c) i) Name the ion that gives a blue colour with the rust indicator. (1mark)Iron(II) ion (1)

ii) Write an equation for the formation of the ion named in (i). (1 mark)Fe(s) Fe 2+(aq) + 2e (1)

d) i) Name the ion that gives a pink colour with the rust indicator. (1mark)Hydroxide ion (1)

ii) Write an equation for the formation of the ion named in (i). (1 mark)

21

O2(g) + H 2O(l) + 2e 2OH (aq) (1)

e) Iron rods X and Y are coated with lead and zinc separately. However, part of thecoating metal has been scratched to expose the iron underneath in each case.

The iron rods are allowed to stand in air for some time.i) Predict whether iron rod X will rust. Explain your answer. (2 marks)The iron rod will rust rapidly (1)as iron is in contact with lead, a less reactive metal. (1)

ii) Predict whether iron rod Y will rust. Explain your answer. (2 marks)

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The iron rod will not rust (1)as zinc provides sacrificial protection. (1)

f) For each of the following iron object, suggest a suitable method to protect it fromrusting:

i) a ship s hull (1 mark)Joining a piece of magnesium (or zinc) to it (1)

ii) bicycle gear wheel (1 mark)Greasing (1)

g) Explain why connecting the steel structure of a pier to the negative terminal of a battery can help protect the steel structure from corrosion. (2 marks)The negative terminal of the battery supplies electrons to the steel structure (1)which prevent the formation of iron(II) ions. (1)

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24 The rusting of iron is investigated by giving five identical iron nails differenttreatments. One nail is left untreated. All six nails are then exposed to air for one week.The results are given in the table below.

Nail Treatment Mass of nail and

coating beforeexposed to air

Mass of nail and

coatingafter exposed toair

A painting 7.0 g 7.3 gB coating with wax 7.0 g 6.5 gC nickel-plating 7.0 g 7.0 gD galvanizing 7.0 g 7.1 gE dipping into salt

solution6.9 g 8.9 g

F untreated 6.9 g 8.2 g

a) Explain why the mass of the untreated nail has increased after exposed to air. (1 mark)Because iron reacts with oxygen and water in air to form rust (hydrated iron(III) oxide). (1)

b) What is the purpose of including an iron nail untreated in the experiment? (1mark)As a control (1)

c) Based on the experimental results, which nail is best protected from rusting?Explain your choice. (2 marks)

The nail coated with nickel. (1)Because the mass of the nickel-plated nail has not increased after exposed to air. (1)

d) Explain in which case was a mistake made in the weighing of the nail. (1mark)

Nail B, since the mass of the nail should be the same or higher after the experiment. (1)

e) Explain why zinc blocks are often attached to the steel legs of off-shore oil platforms. (2 marks)Zinc is more reactive than iron. (1)

It provides sacrificial protection. (1)

f) Explain why rusting is a destructive process but corrosion of aluminium is auseful process. (4 marks)When the rusting of iron occurs, the rust tends to fall off as it is formed. A fresh iron surface is exposed and so rusting goes on. This causes disintegration of the metal. (2)

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When aluminium reacts with oxygen in the air, an even coating of aluminium oxideforms. This oxide layer sticks to the metal surface and is not permeable to oxygen andwater. It protects the metal beneath from further attack. (2)

g) i) Suggest a process to enhance the corrosion resistance of aluminium.

(1 mark)Anodization (1)

ii) Draw a labelled diagram of the laboratory set-up used for this process. (2marks)

(1 mark for correct set-up; 1 mark for correct labels; 0 mark if the set-up is not workable) (2)

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25 Explain briefly how the protection against rusting can be achieved in each of thefollowing cases.a) Underground iron gas pipes are joined to magnesium. (2 marks)This is sacrificial protection. Magnesium corrodes instead of iron (1)

because magnesium is higher than iron in the reactivity series. (1)

b) Cloth hangers are coated with plastic. (2 marks)Plastic acts as a protective layer (1)to prevent air and moisture from reaching the iron and hence prevent rusting. (1)

c) Bus stop signs are painted. (2 marks)Paint gives a protective layer to iron (1)and prevents air and moisture from reaching the iron and hence prevents rusting. (1)

d) Bicycle chains are greased. (2 marks)Grease protects the bicycle chains (1)

by preventing air and water to come into contact with the iron and hence rusting can be prevented. (1)

e) A car body is connected to the negative terminal of a car battery. (2 marks)The negative terminal of the battery supplies electrons to the car body (1)and prevents the formation of iron(II) ions. (1)

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26 Read the passage below and answer the questions that follow.

Sodium

Sodium is the fifth most abundant metal in the Earths crust. Sodium is a soft, bright

and silvery metal.

Sodium is first isolated by Humphry Davy in 1807. He electrolyzed molten sodiumhydroxide and found a lustrous substance formed around one of the electrodes. Davyconducted experiments on the substance and decided that it was a metal.

Sodium is now obtained commercially by the electrolysis of molten sodium chloride.

a) Suggest TWO pieces of experimental evidence that Davy could have used toshow that the lustrous substance was a metal. (2 marks)

Any two of the following:It is a good conductor of electricity. (1) / It is a good conductor of heat. (1) / It ismalleable / ductile. (1) / It can react with water to form hydrogen. (1)

b) Explain why iron was discovered about four thousand years ago while sodiumwas discovered about two hundred years ago. (2 marks)Sodium is more reactive than iron. (1)The extraction of iron is easier than that of sodium. Hence iron was discovered muchearlier than sodium. (1)

c) The cell shown below can be used to carry out the electrolysis of molten sodium

chloride in the laboratory.

i) Describe the observations during the experiment. (2 marks)A greenish yellow gas (chlorine) formed around electrode X. (1)A lustrous substance (sodium) formed around electrode Y. (1)

ii) The cell used is made of silica which has a high melting point. The followingdiagram shows part of a silica lattice.

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Explain why silica has a high melting point. (2 marks)Silica has a giant covalent structure. (1)To melt silica, a lot of heat is needed to overcome the strong covalent bonds between theatoms. (1)

iii) List TWO safety precautions that should be taken for this experiment. (2marks)Wear safety glasses. (1)Take care when handling the high temperature molten sodium chloride. (1)

d) A small piece of sodium is dropped into a trough of water containing litmussolution.i) State TWO expected observations. (2 marks)Any two of the following:Sodium moves rapidly on the water surface. (1) / Sodium melts to form a silvery bead. (1)/ Sodium dissolves in water. (1) / The solution turns blue. (1) / Sodium burns with agolden yellow flame. (1)

ii) Write a chemical equation for the reaction involved. (1 mark)2Na(s) + 2H 2O(l) 2NaOH(aq) + H 2(g) (1)

e) Suppose a piece of sodium is on fire in the laboratory. Suggest a method for putting out the fire. (1 mark)Use sand to cover the burning sodium. (1) / Spray powder from a powder extinguisheronto the burning sodium. (1)

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27 Read the passage below and answer the questions that follow.

Recycling of steel

Recycling steel waste reduces related pollution by about 70%. It takes four times

as much energy to make steel from iron ore than from recycled steel.

Recycling food cans made from tin-plated steel saves 74% of the energy needed to produce these cans from raw materials. 80% of the tin is recovered from recycled cans.

Every time a tonne of steel is recycled, 2 000 kg of iron ore, 500 kg of coal and 20 kg oflimestone are conserved.

a) Explain why mining iron ore causes environmental problems. (3 marks)Any three of the following:Dust caused by mining (1) / noise from blasting and machines (1) / eyesore (1) / destroys

habitats (1) / waste carried by rain run into rivers and lakes causes water pollution (1)

b) Explain why the steel body of a food can is plated with tin. (1 mark)To protect the steel from rusting. (1)

c) Can galvanized iron be used to make food cans? Explain your answer. (2marks)

No. (1)Zinc ions are poisonous. (1)

d) Explain why it is NOT advisable to buy a can of food if there are scratches on the

body of the can. (2 marks)Tin is less reactive than iron. (1)When the tin coating of a food can is damaged, the iron rust more quickly than when it is alone. (1)

e) Explain why as much steel as possible should be recycled. (3 marks)Any three of the following:Cost of raw materials is reduced. (1) / Raw materials (or ores) are conserved. (1) / Fuelcan be saved. (1) / Less air pollution caused by burning fuel. (1) / Environmental impactdue to metal waste and mining can be reduced. (1)

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28 You are provided with the following materials and apparatus:Bunsen burner, test tube holder, wooden splints, test tubes, delivery tube and

limewater

Suggest how you would carry out three chemical tests, using the materials and apparatus

listed above, to distinguish between silver oxide, iron(III) oxide and carbon powder. Youranswer should include the expected observation of each test.(For this question, you are required to give answers in paragraph form.) (9 marks)

Heat the three substances separately in air, (1)silver oxide decomposes to give a solid with metallic lustre (1)and a gas which can relight a glowing splint. (1)Carbon powder will burn to red-hot and a gas is released.Pass the gas into limewater with a delivery tube. It can turn limewater milky. (1)Heat iron(III) oxide with carbon powder, (1)Solids with metallic lustre are formed and a gas is released. The gas can turn limewater

milky. (1)(3 marks for organization and presentation)

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29 Protective coatings are commonly used for preventing rusting. Discuss theunderlying principle involved in TWO kinds of protective coating and their limitations,with reference to specific examples.(For this question, you are required to give answers in paragraph form.) (9 marks)

Oxygen and water must be present for rusting to occur. (1)Protective coatings on iron articles prevent both oxygen and water from reaching the ironunderneath and thus protecting the iron from rusting. (1)

Any TWO of the following: (2 x 2)Example 1:Painting is applied on articles unlikely to be scratched. Cars, bridges and iron railings are

protected from rusting by painting.However, as soon as the paint is scratched, the metal is exposed to air and rusting starts.Therefore painting is not suitable for iron moving parts of machines.

Example 2:For moving parts of machines, such as door hinges and motors, oil or grease is appliedfor preventing rusting. Oil or grease has a lubricating purpose also.However, oil or grease must be reapplied constantly. Therefore this method is unsuitablefor large structures.

Example 3:Coat hangers and dish racks are often protected with a thin coating of plastic. This

protection lasts longer and improves the appearance of the articles.However, coating iron articles with plastic is more expensive than painting.

Example 4:Iron can be coated with a thin layer of tin for preventing rusting. Food cans are usuallymade of mild steel coated with a thin layer of tin because tin ions are non-poisonous.However, once the tin coating is damaged, the iron rusts more quickly than when it isalone. This is because iron is more reactive than tin.

Example 5:Iron can be coated with a layer of zinc for preventing rusting. When the zinc coating isdamaged, zinc still protects the iron from rusting. This is because zinc is more reactivethan iron and corrodes instead of iron.However, iron coated with zinc is not suitable for making food cans because zinc ions are

poisonous.

Example 6:A very thin layer of metal can be applied on iron by electroplating. Chromium- andnickel-platings protect iron from both oxygen and water. These platings are not easilyscratched off. Chromium-plated articles look more attractive.However, the cost of electroplating is quite high.