Structured question

Structured questions1The table below shows information about four different metals A, B, C and D.MetalCostCorrosion resistanceHeat

conductivityMechanical strengthDensity

ALowLowMediumMediumLow

BHighHighGoodHighHigh

CLowMediumMediumHighMedium

DMediumMediumGoodMediumMedium

Which metal is the most suitable for making

a)medal;

b)a gate; and

c)the metal base of a hot pot?

State TWO reasons for your choice in each case.(9 marks)Answer:1a)B

(1)

Any TWO of the following:

(1 ( 2)

High corrosion resistance

High mechanical strength

High density

b)C

(1)

Any TWO of the following:

(1 ( 2)

Cheap

High mechanical strength

Medium density

c)D

(1)

Medium price

(1)

Good conductivity of heat

(1)

2Consider the following metals:

Aluminium, tin, copper, lead, zinc and titanium

For each of the tasks listed below, choose ONE metal which is best for accomplishing thetask. Explain your choice in each case.

a)Making space shuttles

b)Protecting food cans from rusting

c)Making soft drink cans(6 marks)Answer:2a)Titanium

(1)

Very strong / light

(1)

b)Tin

(1)

Non-poisonous

(1)

c)Aluminium

(1)

High corrosion resistance / light

(1)

3The figure shows a piece of electrical wire.

a)Which metal is the most suitable for making electrical wires?

b)Suggest TWO essential properties of that metal which make it suitable for makingelectrical wires.c)Account for the properties mentioned in (b) in terms of metallic bond.

d)Explain with equations, if any, what will happen if this wire is put into

i)dilute hydrochloric acid; and

ii)silver nitrate solution.

(8 marks)Answer:3a)Copper

(1)

b)Very good conductor of electricity

(1)

Very ductile

(1)

c)Copper is a good conductor of electricity because it has mobile electrons.

(1)

Copper is ductile because when the metal is pulled, the copper atom layers

can slide over each other but are still bound together by the sea of electrons.(1)

d)i)No observable change as copper has a very low reactivity.

(1)

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

Cu(s) + 2AgNO3(aq) (Cu(NO3)2(aq) + 2Ag(s)

(1)

or Cu(s) + 2Ag+(aq) ( Cu2+(aq) + 2Ag(s)

4The table below lists some information about three metals A, B and C.MetalABC

Atomic number1220

Heating in airBurns with bright lightBurns with a brick-red flameNo observable change

Reaction with waterNo observable changeGas bubbles are given off, slowly at first but becomes faster after some timeNo observable change

a)To which group in the periodic table do A and B belong?

b)Metal A does not react with water but reacts with steam readily.

i)Write a chemical equation for the reaction between A and steam.

ii)Draw an electron diagram for the solid product formed in (i), showing electronsin the outermost shells only.

c)i)Write an equation for the reaction between B and water.

(An ionic equation will NOT be accepted for this question.)

ii)Draw an electron diagram for the gaseous product formed in the reaction.

iii)Suggest an explanation for the observation made when B reacts with water.

iv)Draw a labelled diagram of the set-up for carrying out the reaction between Band water, with the collection of the gaseous product.

d)Suggest what C might be.

e)Explain, in terms of electronic structure, why B is more reactive than A.(12 marks)Answer:4a)Group II

(1)

b)i)Mg(s) + H2O(g) (MgO(s) + H2(g) /

A(s) + H2O(g) ( AO(s) + H2(g)

(1)

ii)

(1)

c)i)Ca(s) + 2H2O(l) ( Ca(OH)2(s) + H2(g) /

B(s) + 2H2O(l) ( B(OH)2(s) + H2(g)

(1)

ii)

(1)

iii)The calcium metal is covered by a layer of calcium oxide.

(1)

Reaction between calcium and water only starts when the oxide layer dissolves.(1)

iv)

(2)

d)Silver / gold / platinum

(1)

e)An atom of B has one more occupied electron shell than an atom of A. The outermost

shell electrons of an atom of B are further away from the nucleus than those of an atom

of A. In an atom of B, the attraction between the outermost shell electrons and the

nucleus is weaker.

(1)

Therefore, B loses electrons more readily than A.

(1)

5 Results of some reactions of four metals A, B, C and D are shown below:ReactionResult

(i) A(s) + HCl(aq)No reaction

(ii) B(s) + HCl(aq)Reacts steadily to give hydrogen

(iii) A(s) + O2 (g)An oxide is formed when heated

(iv) D(s) + O2 (g)No reaction when heated

(v) B(s) + H2O (g)Reacts slowly with steam

(vi) C(s) + H2O (g)Reacts vigorously with steam

a)Arrange the four metals in descending order of reactivity. Explain briefly.

b)Another metal E reacts with dilute hydrochloric acid to give hydrogen.The solution of a compound of E also shows the following reaction:

B(s) + E2+(aq) ( B2+(aq) + E(s)

Where would you place E in the reactivity series among A, B, C and D?Explain briefly.(7 marks)Answer:

5a)C > B > A > D

(1)

From reactions (v) and (vi), it can be concluded that C is more reactive than B

because C reacts vigorously with steam while B reacts slowly with steam.

(1)

From reactions (i) and (ii), it can be concluded that B is more reactive than A

because B reacts with dilute hydrochloric acid but A does not.

(1)

From reactions (iii) and (iv), it can be concluded that A is more reactive than D

because oxide of A is formed on heating while there is no reaction for D.

(1)

b)E is more reactive than A because E reacts with dilute hydrochloric acid but A

does not.

(1)

E is less reactive than B because B can displace E from a solution of compoundof E.(1)

Thus, E should be placed between B and A in the reactivity series.

(1)6a)For each of the following experiments, state ONE observable change and write achemical equation for the reaction involved.

i)Magnesium is put into dilute hydrochloric acid.

ii)Sodium is heated in a Bunsen flame.

iii)Lead(II) oxide is heated with carbon powder.

iv)Zinc is put into copper(II) sulphate solution.

b)Explain why there is NO reaction in the following experiments.

i)Lead is put into dilute sulphuric acid.

ii)Calcium oxide is heated with carbon powder.

iii)Copper is put into magnesium nitrate solution.(14 marks)Answer:

6a)i)Magnesium dissolves. / Gas bubbles are given off.

(1)

Mg(s) + 2HCl(aq) ( MgCl2(aq) + H2(g)

(1)

ii)A golden yellow flame is observed. / A white smoke is formed.

(1)

4Na(s) + O2(g) ( 2Na2O(s)

(1)

iii)The yellow solid turns orange. / A silvery solid is formed.

(1)

2PbO(s) + C(s) ( 2Pb(s) + CO2(g)

(1)

iv)Zinc dissolves. / A brown solid deposits. / The blue colour of the solution fades

gradually.

(1)

Zn(s) + CuSO4(aq) ( Cu(s) + ZnSO4(aq)

(1)

b)i)Insoluble lead(II) sulphate is formed on the surface of lead.

(1)

It prevents further reaction.

(1)

ii)Calcium oxide is very stable.

(1)

It cannot be reduced by carbon.

(1)

iii)Copper is less reactive than magnesium.

(1)

Copper cannot displace magnesium from solution of magnesium compounds.(1)

7Sodium can be used as a drying agent to remove trace of water in organic solvents. Sodiumis first drawn into a wire and placed in a bottle of organic solvent.

a)Explain, with the help of a chemical equation, why sodium can be used as a dryingagent.b)Explain why sodium can be drawn into wire in terms of its structure.

c)When sodium was drawn into a wire, it appears shiny at first but turns grey afterexposed to air. Explain this observation with a relevant equation.

d)Suggest ONE potential hazard of using this method in drying organicsolvents.(7 marks)Answer:7a)Sodium reacts with water to give sodium hydroxide and hydrogen.

(1)

2Na(s) + 2H2O(l) ( 2NaOH(aq) + H2(g)

(1)

b)The atoms in sodium are packed in layers.

(1)

When the metal is pulled into thin wires, the atom layers can slide over each other but

are still bound together by the sea of electrons.

(1)

c)When sodium is freshly drawn, new surface is exposed as shiny surface. But it is

rapidly oxidized by the air to form oxide.

(1)

4Na(s) + O2(g) ( 2Na2O(s)

(1)

d)Sodium may react explosively with other substances, such as water, in the process of

preparation and disposal.

(1)

8The 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 dilute hydrochloricacid respectively. The gas produced is collected by displacement of water. The height ofgas collected in the first 30 seconds in each case is measured.

The results are shown in the following table.Metalcalciumtinzinccoppernickel

Height (cm) of gas collected in the first 30 seconds5.514.502.5

a)Write a chemical equation for the reaction between zinc and dilute hydrochloric acid.

b)Suggest a test for the gas evolved.

c)Determine the reactivity series in descending order from the result sprovided.

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

e)Explain why it is NOT suitable to use dilute sulphuric acid to replace dilutehydrochloric acid in this experiment.

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

Height (cm) of gas collected in the first 30 seconds5

i)From the result obtained, rewrite the reactivity series.

ii)Suggest what metal X might be.(9 marks)Answer:8a)Zn(s) + 2HCl(aq) ( ZnCl2(aq) + H2(g)

(1)

b)Hydrogen gas gives a pop sound

(1)

with a burning splint.

(1)

c)Calcium > zinc > nickel > tin > copper

(1)

d)Sodium reacts with acids explosively.

(1)

e)When calcium reacts with dilute sulphuric acid, insoluble calcium sulphate will form

on the surface of calcium.

(1)

This prevents the metal from further reaction.

(1)

f)i)Calcium > metal X > zinc > nickel > tin > copper

(1)

ii)Magnesium / aluminium

(1)

9This following table shows the densities of two Group I metals.

MetalDensity (g cm-3)

Lithium (Li)0.53

Rubidium (Rb)1.53

Density of water = 1.0 g cm-3

a)i)Suggest TWO observable differences when lithium and rubidium are added into a

water trough separately.

ii)Account for the differences.

iii)Write a chemical equation for the reaction between rubidium and water.

b)Rubidium is stored in paraffin oil in a bottle with suitable hazard warning labels.

i)Why should rubidium be stored in paraffin oil?

ii)Draw ONE hazard warning label which should appear on the bottle containingrubidium.(8 marks)Answer:9a)i)Rubidium will sink in water but lithium will float on water.

(1)

Rubidium reacts more vigorously than lithium.

(1)

ii)Rubidium is denser than water and lithium is less dense than water.

(1)

The outermost shell electron in a rubidium atom is further away from the nucleus

than that in a lithium atom. This results in a weaker attraction between the nucleus

and the outermost shell electron in a rubidium atom.

(1)

Therefore, rubidium loses electrons more readily than lithium.

(1)

iii)2Rb(s) + 2H2O(l) ( 2RbOH(aq) + H2(g)

(1)

b)i)It prevents rubidium from reacting with moisture and oxygen in air.

(1)

ii)Explosive

(1)

or flammable

10A metal M reacts with very dilute nitric acid to form a solution B and a gas C but M has noreaction with steam. When M is heated with a Bunsen flame, it gives a solid D. The solid isorange when it is hot and yellow when it is cold.

a)Suggest what M, B, C and D might be.

b)Suggest a test for gas C.

c)Write chemical equation(s) for the extraction of metal M from its sulphide.

d)i)Describe what will be observed when a piece of metal M is added to silver nitratesolution.

ii)Write an ionic equation for the reaction involved.(11 marks)Answer:10a)M: lead

(1)

B: lead(II) nitrate solution

(1)

C: hydrogen

(1)

D: lead(II) oxide

(1)

b)It gives a pop sound

(1)

with a burning splint.

(1)

c)2PbS(s) + 3O2(g) ( 2PbO(s) + 2SO2(g)

(1)

2PbO(s) + C(s) ( 2Pb(s) + CO2(g)

(1)

d)i)Lead dissolves. / M dissolves.

(1)

A grey solid deposits.

(1)

ii)Pb(s) + 2Ag+(aq) ( Pb2+(aq) + 2Ag(s)

(1)

11The following table shows information on extraction of metals of the reactivityseries.MetalExtraction MethodEase of extraction

KMethod ADifficult

Easy

Na

Ca

Mg

Al

ZnCarbon reduction

Fe

Pb

Cu

HgHeating the ore

Au

a)Briefly describe the method A used in the extraction of reactive metals.

b)Write a chemical equation for extracting copper from copper(II) oxide bycarbon reduction.c)i)Name another reducing agent that can be used instead of carbon to reducecopper(II) oxide.

ii)Write a chemical equation for the reaction involved.

d)Write a chemical equation for obtaining silver from its oxide by heating alone.

e)Explain whether a reaction occurs in each of the following cases. State ONE

observation if a reaction occurs.

i)Put zinc into silver nitrate solution

ii)Put copper into magnesium nitrate solution

f)State the relationship between the year of discovery and the ease of extraction for ametal.(10 marks)Answer:11a)Electrolysis of the molten ores of metals

(1)

Metal will be obtained at the negative electrode.

(1)

b)2CuO(s) + C(s) ( 2Cu(s) + CO2(g)

(1)

c)i)Hydrogen / carbon monoxide

(1)

ii)CuO(s) + H2(g) ( Cu(s) + H2O(l)

(1)

or CuO(s) + CO (g) ( Cu(s) + CO2(g)

d)2Ag2O(s) ( 4Ag(s) + O2(g)

(1)

e)i)A reaction occurs because zinc is more reactive than silver.

(1)

Zinc dissolves. / A grey solid deposits.

(1)

ii)No reaction occurs because copper is less reactive than magnesium.

(1)

f)The easier the extraction of a metal, the earlier the metal is discovered.

(1)12The 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.

b)Which metal is most likely to be found free in nature? Explain your answer.

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

d)Suggest how metal a can be extracted from its ore.

e)What would be formed when the oxide of metal d is heated with coke?

f)Suggest an experiment to show that metal b is more reactive than iron.

g)Can we store the solution of nitrate of metal c in a container made of metal d?

Explain your answer.

(12 marks)Answer:12a)Metal a

(1)

Because it is the most reactive metal and thus reacts rapidly with oxygen in air to form

an oxide layer on the metal surface.

(1)

b)Metal f

(1)

Because it is the least reactive metal and thus does not form stable compounds readily.

(1)

c)No.

(1)

Iron has no reaction with cold water and metal d is less reactive than iron.

(1)

d)Electrolysis of its molten ore

(1)

e)Metal d is formed.

(1)

f)Add metal b to iron(II) sulphate solution.

(1)

Metal b can displace iron from iron(II) sulphate solution.

(1)

g)Yes.

(1)

Since metal d is less reactive than metal c, no displacement reaction occurs.

(1)

13A student performs several experiments to determine the order of reactivity of five metals(P, Q, R, S and T). The results are shown in the table below.ExperimentMetal

PQRST

Reaction with water Reacts readilyNo reactionNo reactionReacts vigorouslyNo reaction

Reaction with steamReacts readilyNo reactionReacts very slowlyReacts vigorouslyNo reaction

Reaction with dilute hydrochloric acidReacts readilyNo reactionReacts slowlyReacts explosivelyNo reaction

Heating the metal oxide with carbonNo reactionMetal Q obtainedMetal R obtainedNo reactionMetal T obtained

Displacement reactionT displaces Q from the solution of nitrate of Q

a)Arrange the metals in order of reactivity, starting with the most reactive one.

Explain your answer briefly.

b)i)Suggest what metal P might be.

ii)Write a chemical equation for the reaction between metal P and dilutehydrochloric acid.

iii)State TWO observations when metal P is heated in air.

c)i)Suggest what metal S might be.

ii)Write a chemical equation for the reaction between metal S and water.

iii)Suggest how metal S can be extracted from its ore.

d)i)During reactions, metal R forms R2+ ions. Write a chemicalequation for thereaction between metal R and steam.

ii)Draw electron diagrams of the products formed in (i) above, showing electrons inthe outermost shells only.

e)Metal Q forms an oxide with a chemical formula of Q2O.

i)Suggest what metal Q might be.

ii)Would there be any reaction between zinc and the solution of nitrate of Q?Write an ionic equation for the reaction, if any.(18 marks)Answer:13a)S > P > R > T > Q

(1)

P and S are more reactive than Q, R, and T because P and S react with water while Q,

R and T do not.

(1)

S is more reactive than P as S reacts more vigorously with water than P.

(1)

R is more reactive than Q and T because R reacts slowly with dilute hydrochloric acid

while Q and T show no reaction.

(1)

T is more reactive than Q because T displaces Q from the solution of nitrate of Q. (1)

b)i)Calcium

(1)

ii)Ca(s) + 2HCl(aq) ( CaCl2(aq) + H2(g)

(1)

iii)It burns with a brick-red flame.

(1)

A white solid is formed.

(1)

c)i)Sodium / potassium

(1)

ii)2Na(s) + 2H2O(l) ( 2NaOH(aq) + H2(g)

(1)

or 2K(s) + 2H2O(l) ( 2KOH(aq) + H2(g)

iii)Electrolysis of its molten ore

(1)

d)i)R(s) + H2O(g) ( RO(s) + H2(g)

(1)

ii)

(1)

e)i)Silver

(1)

ii)Yes

(1)

Zn(s) + 2Ag+(aq) ( Zn2+(aq) + 2Ag(s)

(1)

14The following tables record the results of some reactions of four different metals and their

oxides.MetalReactionWXYZ

Adding dilute hydrochloric acidVery dangerous! Never attempt No observable changeBubbles given offBubbles given off

Adding copper (II) nitrate solutionBubbles given offNo observable changeMetal dissolves, a brown solid depositsMetal dissolves, a brown solid deposits

Heating the oxide aloneNo observable changeA silvery solid is formedNo observable changeNo observable change

Heating the oxide with carbonNo observable changeA silvery grey solid is formedNo observable change

a)Arrange the four metals in descending order of reactivity. Explain your answer briefly.

b)If Z burns in air with a bright light, suggest what metal Z might be and write achemical equation for its reaction with dilute hydrochloric acid.

c)Draw electron diagrams of the products formed in (b), showing electrons in theoutermost shells only.

d)Explain the observation, with the help of an equation, when metal W is added tocopper(II) nitrate solution.

e)Suggest and explain another observable change when metal Y is added to copper(II)nitrate solution.

(12 marks)Answer:14a)W > Z > Y > X

(1)

Only the oxide of X can be reduced easily by heating alone, therefore X is the least

reactive.

(1)

Y can be obtained by carbon reduction of its oxide, but W and Z cannot. It means that

W and Z are more reactive.

(1)

W is the most reactive since only W reacts vigorously with dilute hydrochloric acid.(1)

b)Magnesium

(1)

Mg(s) + 2HCl(aq) ( MgCl2(aq) + H2(g)

(1)

c)MgCl2:

(1)

H2:

(1)

d)W is so reactive that it reacts with water instead of displacing copper fromcopper(II)

nitrate solution.

(1)

2W(s) + 2H2O(l) ( 2WOH(aq) + H2(g)

(1)

e)The blue colour of the solution fades

(1)

as the concentration of copper(II) ions in the solution decreases.

(1)

15The results of a series of displacement reactions are given in the table below.Salt solutionMetalNitrate of XLead(II) nitrateIron(II) nitrateSilver nitrate

XReaction occursReaction occursReaction occurs

LeadNo observable changeNo observable changeReaction occurs

IronNo observable changeReaction occursReaction occurs

SilverNo observable changeNo observable changeNo observable change

a)What is displacement reaction?

b)List TWO observable changes when X is put into iron(II) sulphate solution.

c)Based on the information given above, arrange the metals in descending order of

reactivity. Briefly explain your answer.

d)Chromium should be placed between X and iron in reactivity series. Suppose you areprovided with chromium(III) nitrate solution, describe an experiment to show this.

e)Write an ionic equation for the reaction between iron and silver nitrate solution.(10 marks)Answer:15a)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)Any TWO of the following:

(1 ( 2)

Metal X dissolves.

A grey solid deposits.

The green colour of the solution fades.

c)X > iron > lead > silver

(1)

X is the most reactive since it can displace all other three metals from solutions of

their salts.

(1)

Iron is more reactive than lead and silver because it can displace lead and silver

from solutions of their salts.

(1)

Silver is the least reactive as it cannot displace any metal.

(1)

d)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)Fe(s) + 2Ag+(aq) ( Fe2+(aq) + 2Ag(s)

(1)16a)Calculate the number of moles of the following substances.

i)1.20 ( 1025 sodium atoms

ii)22.8 g of nitrogen dioxide molecules

iii)4.80 ( 1023 formula units of copper(II) carbonate

iv)13.2 g of hydrated magnesium sulphate (MgSO4(7H2O)

b)Calculate the masses of the following substances.

i)2.00 moles of sodium hydroxide

ii)1.90 ( 1024 ethane molecules (C2H6)

iii)0.400 mole of hydrated sodium carbonate (Na2CO3(10H2O)

iv)3.90 ( 1022 argon atoms

(Relative atomic masses: H = 1.0, C = 12.0, N = 14.0, O = 16.0, Na = 23.0,

Mg = 24.3, S = 32.1, Ar = 40.0; Avogadro constant = 6.02 ( 1023 mol-1)(8 marks)

Answer:16a)i)1.20 ( 1025 6.02 ( 1023 mol-1 = 19.9 mol

(1)

ii)22.8 g (14.0 + 2 ( 16.0) g mol-1 = 0.496 mol

(1)

iii)4.80 ( 1023 6.02 ( 1023 mol-1 = 0.797 mol

(1)

iv)13.2 g [24.3 + 32.1 + 4 ( 16.0 + 7 ( (2 ( 1.0 + 16.0)] g mol-1

= 0.0536 mol

(1)

b)i)2.00 mol ( (23.0 + 1.0 + 16.0) g mol-1 = 80.0 g

(1)

ii)(1.90 ( 1024 6.02 ( 1023) mol ( (2 ( 12.0 + 6 ( 1.0) g mol-1 = 94.7 g

(1)

iii)0.400 mol ( [2 ( 23.0 + 12.0 + 3 ( 16.0 + 10 ( (2 ( 1.0 + 16.0)] g

mol-1 = 114 g

(1)

iv)(3.90 ( 1022 6.02 ( 1023) mol ( 40.0 g mol-1 = 2.59g

(1)17a)In 67.5 g of hydrated aluminium sulphate Al2(SO4)3(6H2O, calculate

i)the number of moles of aluminium ions present;

ii)the number of moles of water molecules present;

iii)the number of sulphur atoms present;

iv)the number of oxygen atoms present; and

v)the number of ions present.

b)When 1.96 g of metal M are completely changed to ions, 3.61 ( 1022 electrons are

released. The relative atomic mass of M is 65.4.

i)What is the number of moles of 1.96 g of M?

ii)What is the number of moles of electrons released?

iii)What is the charge on an ion of M?

(Relative atomic masses: H = 1.0, O = 16.0, Al = 27.0, S = 32.1; Avogadro

constant = 6.02 ( 1023 mol-1)(9 marks)Answer:17a)i)Number of moles of Al2(SO4)3(6H2O

= 67.5 g [ 2 ( 27.0 + 3 ( (32.1 + 4 ( 16.0) + 6 ( (2 ( 1.0 + 16.0)] g mol-1

= 0.150 mol

(1)

Number of moles of aluminium ions = 2 ( 0.150 mol = 0.300 mol

(1)

ii)Number of moles of water molecules = 6 ( 0.150 mol = 0.900 mol

(1)

iii)Number of sulphur atoms = 3 ( 0.150 mol ( 6.02 ( 1023 mol-1

= 2.71 ( 1023

(1)

iv)Number of oxygen atoms = 18 ( 0.150 mol ( 6.02 ( 1023 mol -1

= 1.63 ( 1024

(1)

v)Number of ions = 5 ( 0.150 mol ( 6.02 ( 1023 mol-1 = 4.52 (1023

(1)

b)i)Number of moles of M = 1.96 g 65.4 g mol-1 = 0.0300 mol

(1)

ii)Number of moles of electrons = 3.61 ( 1022 6.02 ( 1023 mol-1

= 0.0600 mol

(1)

iii)The charge on an ion of M = 0.0600 mol 0.0300 mol = +2

(1)

18a)2.70 g of a metal M combines with 2.40 g of oxygen to form an oxide with the formula

M2O3. What is the relative atomic mass of M?

b)A crystalline salt (MCl3(6H2O) is found to contain 40.5% by mass of water of

crystallization. Calculate

i)the formula mass of the hydrated salt; and

ii)the relative atomic mass of the metal M.

(Relative atomic masses: H = 1.0, O = 16.0, Cl = 35.5)

(6 marks)Answer:18a)Let Mr be the relative atomic mass of metal M.

Number of moles of M : number of moles of O = 2 : 3 =:

(1)

Mr = 27.0

(1) or Mass of M in oxide : Mass of oxygen in oxide

= 2.70 : 2.40 = 2Mr : 3 ( 16.0

Mr = 27.0

b)i)Formula mass of the hydrated salt= (6 ( 18.0) 0.405

(1)

= 267

(1)

ii)Relative atomic mass of metal M= 267 (6 ( 18.0 + 3 ( 35.5)

(1)

= 52.5

(1)

19a)10.1 g of hydrated calcium chloride (CaCl2(nH2O) gives 5.00 g of water on strong

heating. Find the value of n.

b) A hydrated salt of copper contains 63.9% by mass of the anhydrous salt. The anhydroussalt has the following percentage composition by mass: copper 39.8%; sulphur 20.1%;oxygen 40.1%. Find the empirical formula of the hydrated salt.

(Relative atomic masses: H = 1.0, O = 16.0, S = 32.1, Cl = 35.5, Ca = 40.1, Cu = 63.5)(8 marks)Answer:19a)Number of moles of CaCl2 : Number of moles of H2O = 1 : n

Number of moles of CaCl2 = 5.10 g (40.1 + 2 ( 35.5) g mol-1

= 0.0459 mol

(1)

Number of moles of H2O = 5.00 g 18.0 g mol-1 = 0.278 mol

(1)

1 : n = 0.0459 : 0.278

n = 6

(1)

b)Suppose there are 100 g of anhydrous salt.CopperSulphurOxygen

Mass of element39.8 g20.1 g40.1 g

Number of moles of atoms that combine39.8 g 63.5 g mol-1 = 0.627 mol20.1 g 32.1g mol-1 = 0.626 mol40.1 g 16.0 g mol-1 = 2.51 mol

Simplest whole number ratio of atoms0.627 0.626 = 10.626 0.626 = 12.51 0.626 = 4

So the empirical formula of the anhydrous salt is CuSO4.

Formula mass of the hydrated salt = (63.5 + 32.1 + 4 ( 16.0) 0.639 = 250

(1)

Let the empirical formula of the hydrated salt be CuSO4(6H2O.

63.5 + 32.1 + 4 ( 16.0 + 18n = 250

(1)

n = 5

The empirical formula of the hydrated salt is CuSO4(5H2O.

(1)

20The following diagram shows the set-up used in an experiment to determine the empirical formula of a black copper oxide.

Town gas (main constituents being carbon monoxide and hydrogen) was passed over theoxide before heating. The black copper oxide was reduced to copper in the experiment.Heating was stopped after some time. Town gas was passed over the copper until it was cold. The results are as follows:Mass of tube = 25.20 gMass of tube and copper oxide= 27.78 gMass of tube and copper formed= 27.26 g

a)Why was town gas passed over the chemical before and after the experiment?

b)State an expected observation in this experiment.

c)Suggest ONE test to show that a metal is formed in this experiment.

d)Write appropriate equations to account for the chemical change of thecopper oxide.

e)Calculate the number of moles of copper formed.

f)Calculate the number of moles of oxygen present in the copper oxide.

g)From the results of (e) and (f), determine the empirical formula of the copper oxide.

h)List TWO potential hazards of this experiment.

(Relative atomic masses: O = 16.0, Cu = 63.5)(11 marks)Answer:20a)Before experiment: To flush the air out because a mixture of town gas and air may

explode on ignition.

(1)

After experiment: To prevent oxidation of the copper by air again.

(1)

b)The black oxide changed to reddish brown metal.

(1)

c)The metal obtained can conduct electricity.

(1)

d)CuO(s) + CO(g) ( Cu(s) + CO2(g)

(1)

CuO(s) + H2(g) ( Cu(s) + H2O(l)

(1)

e)Number of moles of copper formed = (27.26 25.20) g 63.5 g mol-1

= 0.0324 mol

(1)

f)Number of moles of oxygen in the oxide = (27.78 27.26) g 16.0 g mol-1

= 0.0325 mol

(1)

g)Mole ratio of copper to oxygen = 0.0324 : 0.0325 = 1 : 1

So the empirical formula of the copper oxide is CuO.

(1)

h)Town gas is toxic (carbon monoxide) and explosive (hydrogen).

(1, 1)

21The following set-up was used to determine the empirical formula of an oxide of cobalt(Co).

The experimental results were as follows:

(1)Mass of crucible + lid = 20.49 g

(2)Mass of crucible + lid + cobalt = 23.13 g

(3)Mass of crucible + lid + oxide of cobalt = 24.09 g

a)Give TWO reasons why the crucible should be half covered with the lid duringheating, as shown in the diagram.

b)Calculate the empirical formula of the oxide of cobalt.

c)Cobalt-60 is widely used as a medical and industrial radiation source.

Complete the following information for a 60Co atom.Number of protonsNumber of neutrons

(i)(ii)

(Relative atomic masses: O = 16.0, Co = 58.9)(7 marks)Answer:21a)To ensure there is enough oxygen to react with cobalt.

(1)

To prevent the loss of the oxide formed.

(1)

b)CobaltOxygen

Number of moles of atoms that combine2.64 g 58.9 g mol-1 = 0.0448 mol0.960 g 16.0 g mol-1 = 0.0600 mol

Simplest ratio of atoms0.0448 mol 0.0448 mol = 10.0600 mol 0.0448 mol = 1.34

Simple whole number ratio of atoms34

The empirical formula of the cobalt oxide is Co3O4.

c)i)27

(1)

ii)33

(1)

22a)Both nitrogen and fluorine are non-metals. Draw electron diagrams of the followingmolecules:

i)a nitrogen molecule

ii)a fluorine molecule

b)Nitrogen can form a fluoride with relative molecular mass of 66.0. The compoundcontains 42.4% of nitrogen by mass.

i)Deduce the molecular formula of the compound.

ii)Draw an electron diagram of the compound, showing electrons in the outermost

shells only.

(Relative atomic masses: N = 14.0, F = 19.0)(6 marks)Answer:22a)i)

(1)

ii)

(1)

b)i)Suppose there are 100 g of the fluoride, so there are 42.4 g of nitrogen and 57.6 g

of fluorine.NitrogenFluorine

Number of moles of atoms that combine42.4 g 14.0 g mol-1 = 3.03 mol57.6 g 19.0 g mol-1 = 3.03 mol

Simplest ratio of atoms3.03 mol 3.03 mol = 13.03 mol 3.03 mol = 1

(The empirical formula of the fluoride is NF.

Let (NF)n be the molecular formula of the fluoride.

Relative molecular mass of the fluoride= n (14.0 + 19.0) = 66.0

(n = 2

(1)

(The molecular formula of the fluoride is N2F2.

ii)

23A piece of copper of mass 26.78 g was immersed in a colourless solution of nitrate of metalX in a beaker. A silvery deposit of X formed on the copper surface and the solutiongradually turned pale blue. The beaker was allowed to stand. X was then washed withdistilled water and dried. The mass of X obtained was 1.94 g and the remaining copper hada mass of 26.21 g.

a)Explain why the solution gradually turned pale blue.

b)Calculate the mass of copper reacted with the nitrate of X.

c)i)Explain why the solution was allowed to stand.

ii)Explain why the solid X should be washed and dried.

d)What is the number of moles of copper reacted?

e)What is the number of moles of X obtained?

f)What is the number of moles of X obtained when 1 mole of copper(II) ions is formed?

g)Write an ionic equation for the above reaction.

(Relative atomic masses: Cu = 63.5, X = 107.9)(10 marks)Answer:23a)Copper reacted and blue copper(II) ions were formed.

(1)

b)(26.78 26.21) g = 0.570 g

(1)

c)i)To allow the solid formed to settle and deposit on the bottom of beaker.

(1)

ii)Washing helps to remove any water soluble impurities.

(1)

Drying allows the water in solid X to evaporate off, so more accurate result can be

obtained.

(1)

d)0.570 g 63.5 g mol-1 = 8.98 ( 10-3 mol

(1)

e)1.94 g 107.9 g mol-1 = 0.0180 mol

(1)

f)Mole ratio of X to Cu = 0.0180 : 8.98 ( 10-3 = 2 : 1

(1)

Number of moles of X obtained = 2 mol

(1)

g)Cu(s) + 2X+(aq) ( Cu2+(aq) + 2X(s)

(1)

24A student tried to extract lead from lead(II) oxide. He placed 10.0 g of lead(II) oxide and10.0 g of carbon powder in a crucible and heated the mixture with a Bunsen flame.

a)Draw an experimental set-up for the extraction of lead(II) oxide.

b)i)Write a chemical equation for the reaction involved.

ii)Suggest ONE observation for the reaction.

c)i)Determine which reagent is in excess.

ii)Calculate the maximum mass of lead that could be obtained.

d)In fact, the student only obtained 7.10 g of lead.

i)Calculate the percentage yield of the reaction.

ii)Suggest ONE reason why the student cannot get the maximum mass of lead.e)Another oxide of lead has a chemical formula of Pb3O4.

Pb3O4 is known to be a mixed oxide composed of PbO and PbO2. Deduce the moleratio of PbO to PbO2 in Pb3O4.

(Relative atomic masses: C = 12.0, O = 16.0, Pb = 207.2)

(12 marks)Answer:24a)

(2)

b)i)2PbO(s) + C(s) ( 2Pb(s) + CO2(g)

(1)

ii)Shiny pieces of solids would be observed.

(1)

c)i)Number of moles of PbO = 10.0 g 223.2 g mol-1 = 0.0448 mol

(1)

Number of moles of C = 10.0 g 12.0 g mol-1 = 0.833 mol

(1)

According to the equation, 2 moles of PbO react with 1 mole of C.

Hence, 0.0448 mole of PbO would react with 0.0224 mole of C.

Therefore, carbon is in excess.

(1)

ii)Maximum mass of Pb obtained = 0.0448 mol ( 207.2 g mol -1 = 9.28 g

(1)

d)i)Percentage yield of reaction=

= 76.5%

(1)

ii)The temperature is not high enough. / Not enough time allowed for the reaction to

take place.

(1)

e)Let the mole ratio of PbO : PbO2 be x : y.

==

x = 2, y = 1

(1)

( Pb3O4 is a mixture of PbO and PbO2 in a mole ratio of 2 : 1.

(1)

25a)Hydrogen can reduce copper(II) oxide to copper. The experiment can be carried outusing the set-up shown below.

i)Write a chemical equation for the reaction between hydrogen and copper(II) oxide.

ii)Suggest why it is necessary to burn the residual hydrogen in the set-up.

iii)What mass of copper would be obtained if 9.54 g of the oxide were consumed inthe reaction?b)Hydrogen is also used to manufacture ammonia by reacting with nitrogen according tothe following equation:

N2(g) + 3H2(g) 2NH3(g)

i)What does the sign in the equation stand for?

ii)In the manufacturing process, a sufficient amount of hydrogen is allowed to reactwith 560 g of nitrogen. 102 g of ammonia are obtained. What is the percentageconversion of nitrogen to ammonia?

(Relative atomic masses: H = 1.0, O = 16.0, N = 14.0, Cu = 63.5)(8 marks)Answer:25a)i)CuO(s) + H2(g) ( Cu(s) + H2O(l)

(1)

ii)Hydrogen is explosive / flammable.

(1)

iii)Number of moles of CuO consumed= Number of moles of Cu obtained

= 9.54 g (63.5 + 16.0) g mol-1

= 0.120 mol

(1)

Mass of copper obtained= 0.120 mol ( 63.5 g mol-1

= 7.62 g

(1)

b)i)The reaction is reversible.

(1)

ii)Number of moles of N2 reacted = 560 g (2 ( 14.0 g) mol-1

= 20.0 mol

(1)

Theoretical yield of NH3= 17.0 g mol-1( 2 ( 20.0 mol

= 680 g

(1)

Percentage conversion of N2 to NH3 = ( 100%

= 15.0%

(1)26Compounds of manganese (Mn) have important uses in industry. Manganese nodules arewidely dispersed on the floor of some deep oceans. Manganese is resent in the nodulesmainly as a form of manganese(IV) oxide MnO2. A nodule of mass 15.0 g was found tocontain 0.0400 mole of manganese(IV) oxide.

a)Calculate the percentage by mass of manganese(IV) oxide in the nodule.

b)Manganese has a hydrated sulphate with the formula MnSO4(nH2O. On strong heating,20.1 g of the sulphate produced 7.51 g of water. What is the value of n?(Relative atomic masses: H = 1.0, O = 16.0, S = 32.1, Mn = 54.9)

c)Pure manganese slowly reacts with cold water, in a way similar to calcium. In anexperiment, a few pieces of calcium granules are added to a beaker of cold water.

i)Give TWO observations when calcium reacts with cold water.

ii)Give a chemical equation for the reaction of calcium with water.

iii)Draw a labelled diagram of the set-up for conducting the experiment andcollecting the gas produced.

iv)Sodium also reacts with cold water. State TWO differences in observation whensodium and calcium are added separately to cold water.(11 marks)Answer:26a)Mass of MnO2 in the nodule= 0.0400 mol ( 86.9 g mol-1

= 3.48 g

(1)

Percentage by mass of MnO2 in the nodule= ( 100%

= 23.2%

(1)

b)

(1)

n = 5

(1)

c)i)Any TWO of the following:

(1 ( 2)

Gas bubbles are given off.

Calcium dissolves.

A milky suspension is formed.

Calcium sinks in water.

ii)Ca(s) + 2H2O(l) ( Ca(OH)2(s) + H2(g)

(1)

iii)

(2)

iv)Sodium floats on the surface of water while calcium sinks.

(1)

Sodium moves rapidly on the surface of water and may burn with a golden yellow

flame. Calcium stays at the bottom of the beaker and does not move.

(1)

27Tin (Sn) displaces copper from copper(II) sulphate solution. Cadmium (Cd) displaces tin from tin(II) chloride solution. The three metals and their cations are as follows:

Sn / Sn2+, Cu / Cu2+, Cd / Cd2+.

a)Write ionic equations for the two displacement reactions described above.

b)Use the information given, deduce the reactivity order of the metals, starting with themost reactive one.

c)State whether you would expect each of the following reactions to occur. Explain your answers.

i)Sn(s) + Cd2+(aq) ( Sn2+(aq) + Cd(s)

ii)Cd(s) + Cu2+(aq) ( Cd2+(aq) + Cu(s)

d)Explain why copper(II) sulphate solution CANNOT be stored in tin containers.

e)Aluminium can also displace copper from copper(II) sulphate solution.

i)Write a chemical equation for the reaction involved.

ii)What is the percentage yield of copper in a reaction which produces

2.58 g of copper from 1.61 g of aluminium and excess copper(II) sulphate solution.

(Relative atomic masses: Al = 27.0, Cu = 63.5)(10 marks)Answer:27a)Sn(s) + Cu2+(aq) ( Sn2+(aq) + Cu(s)

(1)

Cd(s) + Sn2+(aq) ( Cd2+(aq) + Sn(s)

(1)

b)Cd > Sn > Cu

(1)

c)i)No reaction. As tin is less reactive than cadmium, it cannot displace

cadmium from the solution of a cadmium compound.

(1)

ii)It will occur. As cadmium is more reactive than copper, it can displace

copper from the solution of a copper compound.

(1)

d)Tin will react with copper(II) sulphate solution and will eventually wear away.(1)

e)i)2Al(s) + 3CuSO4(aq) ( Al2(SO4)3(aq) + 3Cu(s)

(1)

ii)Number of moles of Al reacted = 1.61 g 27.0 g mol-1

= 0.0596 mol

(1)

Theoretical yield of Cu= 0.0596 (mol ( 63.5 g mol-1

= 5.68 g

(1)

Percentage yield of Cu= ( 100%

= 45.4%

(1)

28a)Calcite is a very pure form of calcium carbonate which reacts with dilute hydrochloricacid according to the following equation:

CaCO3(x) + 2HCl(aq) ( CaCl2(y) + H2O(z) + CO2(g)

2.60 g of calcite were added to 0.0150 mole of hydrochloric acid in a beaker.

Calcite was in excess.

i)Give the state symbols represented by x, y and z in the equation.

ii)Calculate the mass of calcite left unreacted.

iii)Describe what could be done to check the result obtained in (b).

b)An experiment was carried out to determine the percentage by mass of

calcium carbonate in a sample of mass 3.10 g. The set-up shown below was used:

The graph shows the results obtained in the experiment.

i)Find, from the graph, the mass of gas liberated from the reaction of the sample withhydrochloric acid.

ii)Calculate the percentage by mass of calcium carbonate in the sample.

iii)Suggest ONE source of error in the experiment.

(Relative atomic masses: C = 12.0, O = 16.0, Ca = 40.1)(10 marks)Answer:28a)i)x : s, y : aq, z : l.

(1)

ii)Number of moles of calcite added= 2.60 g 100.1 g mol-1

= 0.0260 mol

(1)

According to the equation, 1 mole of CaCO3 reacts with 2 moles of HCl.

0.0150 mole of HCl reacts with 0.00750 mole of CaCO3.

Number of moles of calcite left = (0.0260 0.00750) mol

= 0.0185 mol

(1)

Mass of calcite left= 0.0185 mol ( 100.1 g mol-1

= 1.85 g

(1)

iii)Separate calcite from the reaction mixture, dry and weigh it.

(1)

b)i)1.10 g (187.6 g 186.5 g)

(1)

ii)Number of moles of CO2 liberated= 1.10 g 44.0 g mol-1

= 0.0250 mol

(1)

According to the equation, 1 mole of CaCO3 produces 1 mole of CO2.

Thus 0.0250 mole of CaCO3 produces 0.0250 mole of CO2 in the reaction.

Number of moles of CaCO3 in the sample = 0.0250 mol

Mass of CaCO3 in the sample= 0.0250 mol ( 100.1 g mol-1

= 2.50 g

(1)

Percentage by mass of CaCO3 in the sample= ( 100%

= 80.6%

(1)

iii)Some carbon dioxide dissolve in the acid.

(1)

29Potassium is obtained from the mineral carnallite (KCl(MgCl2(6H2O). An experiment wascarried out to determine the percentage by mass of carnallite in an impure sample. The massof the impure sample was 6.17 g. It was dissolved in water. An excess of acidified silvernitrate solution was added. The silver chloride precipitate was filtered, washed and dried.It had a mass of 8.61 g.

a)i)Silver ion and chloride ion react to give silver chloride according to the followingequation:

Ag+(x) + Cl-(y) (AgCl(z)

Give the state symbols represented by x, y and z in the equation.

ii)Explain why an excess of silver nitrate solution was used in the experiment.

iii)Calculate the number of moles of silver chloride obtained in the experiment.

iv)Calculate the percentage by mass of carnallite in the impure sample.

(Relative atomic masses: H = 1.0, O = 16.0, Mg = 24.3, Cl = 35.5, K = 39.1, Ag = 107.9)b)Suggest how potassium is extracted from carnallite.

c)In another experiment, potassium is heated in the air.

i)Describe the observable changes of the experiment.

ii)Write a chemical equation for the reaction involved.

iii)Suggest how potassium should be stored in the laboratory.(11 marks)Answer:29a)i)x : aq, y : aq, z : s.

(1)

ii)To react with all the chloride ions.

(1)

iii)Number of moles of AgCl = 8.61 g 143.4 g mol-1

= 0.0600 mol

(1)

iv)1 mole of KCl(MgCl2(6H2O contains 3 moles of chloride ions.

1 mole of KCl(MgCl2(6H2O gives 3 moles of AgCl when reacted with excess

AgNO3(aq).

Number of moles of KCl(MgCl2(6H2O in the sample=mol

= 0.0200 mol

(1)

Mass of KCl(MgCl2(6H2O in the sample

= 0.0200 mol ( [39.1 + 24.3 + 3 ( 35.5 + 6 ( (2 (1.0 + 16.0)] g mol-1

= 5.56 g

(1)

Percentage by mass of KCl(MgCl2(6H2O in the sample

= ( 100%

= 90.1%

(1)

b)Electrolysis of molten carnallite

(1)

c)i)Potassium burns vigorously with a purple flame.

(1)

A white smoke forms.

(1)

ii)4K(s) + O2(g) ( 2K2O(s)

(1)

iii)Store it in paraffin oil.

(1)

30Explain each of the following:

a)Aluminium does NOT react with steam unless when the aluminium is washed with

mercury(II) chloride solution.

b)Silver nitrate solution CANNOT be kept in an iron bucket.

c)Aluminium, rather than copper, is used in making overhead power cables.

d)When calcium reacts with dilute sulphuric acid, gas bubbles are given off for a shortwhile and then stop.

e)Zinc can be extracted from its molten ore by electrolysis. Yet in practice, it is usuallyextracted by heating its oxide with coke.

f)It is NOT advisable to buy a can of food if there are scratches on the iron body of thecan.

g)Galvanized iron is NOT used in making food cans.(12 marks)Answer:30a)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)There is a displacement reaction between silver nitrate solution and iron.

(1)

It will cause the iron to dissolve.

(1)

c)Aluminium is lighter and stronger than copper.

(1, 1)

d)Insoluble calcium sulphate forms in the reaction.

(1)

It covers the calcium metal and prevents further reaction.

(1)

e)Electrolysis is an expensive extraction method.

(1)

f)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)Zinc ions are toxic.

(1)

31a)

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 is formed whichbecomes white when cold. 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.

(2)Give the names of compound X and gas Y.

ii)In Stage II, X is heated strongly with a black powder.

(1)Identify the black powder.

(2)Write a chemical equation for the reaction occurred in Stage II.

iii)State ONE use of zinc.b)Statues A and B are mainly made of iron. It is found that statue A rusts more quicklythan B.

i)Give a reason for this.ii)Suggest ONE method to slow down the corrosion of the statues.

c)Zinc reacts with dilute hydrochloric acid to give hydrogen.

i)Write a chemical equation for the reaction involved.

ii)A sample of hydrochloric acid containing 2.92 g of HCl is added to 3.27 g ofzinc. Calculate the mass of hydrogen produced.(Relative atomic masses: H = 1.0, Cl = 35.5, Zn = 65.4)(14 marks)Answer:31a) i)(1)2ZnS(s) + 3O2(g) ( 2ZnO(s) + 2SO2(g)

(1)

(2)X: Zinc oxide

(1)

Y: Sulphur dioxide

(1)

ii)(1)Carbon

(1)

(2)2ZnO(s) + C(s) ( 2Zn(s) + CO2(g)

(1)

iii)Making galvanized iron / casings of dry cells

(1)

b)i)Wind brings acidic sulphur dioxide gas to statue A but not B.

(1)

Acidic gas speeds up the corrosion of iron.

(1)

ii)Metal-plating of the statues

(1)

c)i)Zn(s) + 2HCl(aq) ( ZnCl2(aq) + H2(g)

(1)

ii)Number of moles of HCl used= 2.92 g 36.5 g mol-1

= 0.0800 mol

(1)

Number of moles of Zn used= 3.27 g 65.4 g mol-1

= 0.0500 mol

(1)

According to the equation, 1 mole of Zn reacts with 2 moles of HCl.

Hence, 0.0800 mole of HCl reacts with 0.0400 mole of Zn. Therefore, Zn is in

excess.

(1)

Mass of hydrogen produced= 0.0800 mol 2 ( 2.0 g mol-1

= 0.0800 g

(1)

32Explain briefly how the protection against rusting can be achieved in each of the followingcases.

a)Underground iron gas pipes are joined to magnesium.

b)Cloth hangers are coated with plastic.

c)Bus stop signs are painted.

d)Bicycle chains are greased.

e)A car body is connected to the negative terminal of a car battery.(10 marks)Answer:32a)This is sacrificial protection. Magnesium corrodes instead of iron

(1)

because magnesium is higher than iron in the reactivity series.

(1)

b) Plastic acts as a protective layer

(1)

to prevent air and moisture from reaching the iron and hence prevent rusting.

(1)

c)Paint gives a protective layer to iron

(1)

so that iron can be kept away from direct contact with air and moisture, hence rusting

can be prevented.

(1)

d)Grease protects the moving iron parts

(1)

by preventing air and water to come into contact with the iron, hence rusting can be

prevented.

(1)

e)The negative terminal of the battery supplies electrons to the car body

(1)

which prevent it from being oxidized.

(1)

33Three test tubes are set up in the diagram shown below:

The tubes are left for three days.

a)In which tube(s) will rusting occur?

b)What is the function of the anhydrous calcium chloride used in test tube A?

c)What is the function of the oil used in test tube B?

d)Suggest TWO conditions needed for rusting.

e)Draw a labelled diagram of a set-up that can be used to show that the presence of ionicsubstances can increase the rate of rusting. State also the expected observation.(7 marks)Answer:33a)Tube C

(1)

b)To absorb the moisture in the air in the tube.

(1)

c)To prevent the oxygen in the air from dissolving into the boiled water.

(1)

d)Water and oxygen

(1, 1)

e)

(1)

Compare the degree of rusting of the nail with that in tube C after a certain period of

time. The nail in this tube forms more rust.

(1)

34The rusting of iron is investigated by giving five identical iron nails different treatments.One nail is left untreated. All six nails are then exposed to air for one week. The results aregiven in the table below.NailTreatmentMass of nail and coating before exposed to airMass of nail and coating after exposed to air

APainting7.0 g7.3 g

BCoating with wax7.0 g6.5 g

CNickel-plating7.0 g7.0 g

DGalvanizing7.0 g7.1 g

EDipping into salt solution6.9 g8.9 g

FUntreated6.9 g8.2 g

a)Explain why the mass of the untreated nail has increased after exposed to air.

b)Which nail is best protected from rusting? Explain your answer.

c)Which treatment make the nail rust faster? Explain your answer.

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

e)What is meant by the treatment galvanizing?

f)Bridges are protected from rusting by attaching blocks of magnesium to them.

i)What is the term used to describe this kind of protection against rusting?

ii)Suggest why this method is NOT used to protect iron nails fromrusting.

g)Explain why rusting is a destructive process but corrosion of aluminium is a usefulprocess.(14 marks)Answer:34a)Because iron reacts with oxygen and water in air to form rust (hydrated iron (III)

oxide).

(1)

Formation of hydrated iron (III) oxide has increased the mass of the nail.

(1)

b)The nail coated with nickel.

(1)

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

c)Dipping into salt solution.

(1)

The presence of ionic substances speeds up rusting.

(1)

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

e)Coating the iron with zinc.

(1)

f)i)Sacrificial protection

(1)

ii)It is expensive.

(1)

g)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)

When aluminium reacts with oxygen in the air, an even coating of aluminium oxide

forms. This oxide layer sticks to the metal surface and is not permeable to oxygen and

water. It protects the metal beneath from further attack.

(2)

35Aluminium and iron are the two most abundant metals in the Earths crust.

a)Explain why iron was discovered about four thousand years ago while aluminium was

discovered less than two hundred years ago.

b)Both aluminium and iron can be used to make window frames.

i)Suggest how each metal is treated to prevent corrosion in this usage.

ii)Explain why most window frames are now made of aluminium instead of iron.

c)The diagram below shows a can of fruit juice. The body of the can is made of ironcoated with tin. The top of the can and the ring-pull are made of aluminium.

i)Suggest ONE reason why the iron body is coated with tin.

ii)Suggest ONE reason why aluminium, rather than iron, is used for making the

ring-pull.

iii)There is a trend for manufacturers to use cans made entirely of aluminium for

fruit juice storage. Suggest ONE advantage and ONE disadvantage of this action.(10 marks)Answer:35a)Aluminium is more reactive than iron.

(1)

The extraction of iron is easier than that of aluminium. Therefore, iron was discovered

much earlier than aluminium.

(1)

b)i)The aluminium undergoes anodization to increase the thickness of the oxide layer.

This makes the aluminium much more resistant to corrosion.

(1)

The iron is painted so as to prevent oxygen and water from reaching it.

The paint layer protects the iron beneath from rusting.

(1)

ii)As soon as the paint on the iron is scratched, rusting starts.

(1)

Aluminium reacts with oxygen in the air to give an even coating of oxide on the

surface. The oxide layer is not permeable to oxygen and water. It protects the

metal beneath from further attack.

(1)

c)i)To protect iron from rusting.

(1)

ii)Aluminium is softer than iron so that the ring-pull can be pulled off more easily.(1)

iii)Advantage (Any one of the following):

(1)

Aluminium is lighter than iron.

Aluminium can be recycled more easily.

Aluminium is more corrosion resistant than iron.

Aluminium can be dyed more easily.

Disadvantage (Any one of the following):

(1)

Aluminium is more expensive than iron.

Aluminium is not as strong as iron.

36Aluminium is the most abundant metal in the Earths crust.

a)i)Name an aluminium ore.

ii)Suggest how aluminium can be extracted from its ore.

b)One of the special properties of aluminium is that it has high corrosion resistance.

i)Explain why aluminium has such a high corrosion resistance.

ii)The corrosion resistance of aluminium can be further improved by a method.

(1)Name this method.

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

c)The reaction of aluminium and zinc nitrate solution can be represented by the

following equation:

2Al(s) + 3Zn(NO3)2(aq) ( 2Al(NO3)3(aq) + 3Zn(s)

i)Give TWO observations of the above reaction.

ii)Explain why the above reaction is a displacement reaction.

iii)If 9.00 g of aluminium are added to excess zinc nitrate solution,calculate the

maximum amount of zinc that can be obtained.

(Relative atomic masses: Al = 27.0, Zn = 65.4)(12 marks)Answer:

36a)i)Bauxite

(1)

ii)Electrolysis of molten aluminium oxide

(1)

b)i)There is a layer of aluminium oxide attached to the metal surface.

(1)

ii)(1)Aluminium anodization

(1)

(2)

(2)

c)i)Aluminium dissolves.

(1)

A grey metal deposits.

(1)

ii)The more reactive aluminium displaces the less reactive zinc from zinc nitrate

solution.

(1)

iii)Number of moles of aluminium added= 9.00 g 27.0 g mol-1

= 0.333 mol

(1)

Number of moles of zinc formed= 0.333 mol (

= 0.500 mol

(1)

Maximum mass of zinc obtained= 0.500 mol ( 65.4 g mol-1

= 32.7 g

(1)37You 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.Your answer should include the expected observation of each test.

(You are required to give a paragraph-length answer. For this question, 6 marks will beawarded for chemical knowledge and 3 marks for effective communication.)(You are NOT required to write chemical equations. Answers in the form of flow diagramswill NOT be marked.)(9 marks)Answer:37Heat the three substances alone in air,

(1)

silver oxide will decompose into silvery solids and a gas which can relight a glowing splint is released.

(1)

Carbon powder will burn to red-hot and a gas is released. Pass the gas into limewater with a delivery tube.

(1)

It can turn limewater milky.

(1)

Heat iron (III) oxide with carbon powder,

(1)

the black solid will turn into a silvery-grey solid and a gas is released. The gas can turn limewater milky.

(1)

(3 marks for effective communication)

38You are provided with the following materials and apparatus:

3 clean iron nails, magnesium ribbon, copper foil, gel solution, rust indicator and 3 petri dishes

Suggest an experiment, with the expected observation and explanations, which allows youto determine the reactivity order of magnesium, iron and copper.

(You are required to give a paragraph-length answer. For this question, 6 marks will beawarded for chemical knowledge and 3 marks for effective communication.)(Answers in the form of flow diagrams will NOT be marked.)(9 marks)Answer:38Wrap two iron nails with magnesium ribbon and copper foil separately.

(1)

Place an iron nail and the two wrapped iron nails into three petri dishes separately. Pour gel

solution mixed with rust indicator to each petri dish until each iron nail is completely

covered.

(1)

Leave the dishes for about one to two days.

(1)

The indicator shows a blue colour when rusting occurs. The reactivity can be determined by

observing the presence of blue colour near the iron nails.

(1)

The more reactive metal (Mg) can protect the iron nail from rusting. Therefore, no blue

colour will be observed near the iron nail wrapped with magnesium.

(1)

The less reactive metal (Cu) will speed up the rusting process. Therefore, a blue colour will

be observed quickly near the iron nail wrapped with copper.

(1)

The reactivity order is thus Cu < Fe < Mg.

(3 marks for effective communication)

39Protective coatings are commonly used for preventing rusting. Discuss the underlyingprinciple involved in TWO kinds of protective coating and their limitations, with referenceto specific examples.(You are required to give a paragraph-length answer. For this question, 6 marks will beawarded for chemical knowledge and 3 marks for effective communication.)(9 marks)Answer:39Oxygen and water must be present for rusting to occur.

(1)

Protective coatings on iron articles prevent both oxygen and water from reaching the iron

beneath and thus protecting the iron from rusting.

(1)

Any TWO of the following:

(2 ( 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 machine, such as door hinges and motors, oil or grease is applied for

preventing rusting. Oil or grease has a lubricating purpose also.

However, oil or grease must be reapplied constantly. Therefore, this method is unsuitable

for 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 usually

made 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 is alone. 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 is

damaged, zinc still protects the iron from rusting. This is because zinc is more reactive than

iron and corrodes instead of iron. The protection lasts as long as the zinc lasts.

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- and nickel-platings protect iron from both oxygen and water. These platings are not easily

scratched off. Chromium-plated articles look more attractive.

However, the cost of chromium-plating is quite high.

(3 marks for effective communication)

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