3.2.7 The extraction of metals - MrMortonSciencemrmortonscience.weebly.com/uploads/3/1/5/7/31575951/_3.2...3.2.7 The extraction of metals Principles of metal extraction 314 €minutes

3.2.7 The extraction of metals

Principles of metal extraction

314 minutes

308 marks

Page 1 of 37

M1. (a) (i) C + O2 → CO

2 (1)

(ii) Fe2O

3 + 3C → 2Fe + 3CO etc (1)

Allow oxides FeO, Fe2O

3, Fe

3O

4

(iii) Mg + S → MgS (1)

(iv) Removal of carbon: Oxygen (1) Blown through / bubbled through liquid / molten iron (1)

molten iron, or bubbled through

Reason: Carbon makes iron brittle (1) 6

(b) (i) (Titanium) carbide is formed (1) Allow C bonds / reacts with Ti

(ii) Equation: TiO2 + 2C (or C) + 2Cl

2 → TiCl

4 + 2CO (or CO

2) (1)

(1) All species correct (1) Balanced equation

Condition: High temperature (1) or (700 – 1100°C)

NOT “heat” Mark independently

4

(c) Use of carbon: As cathode / anode / electrodes (1)

Half-equation: Al3+ +3e– → Al (1)

2

(d) Factor 1: Cost of reductant (1)

Factor 2: Cost of energy (1)

Factor 3: Purity of metal (1) or reactivity of metal (1) max 3

[15]

Page 2 of 37

M2. (a) Essential steps: Four equations (4) Three stated raw materials (3) Three statements of use (3)

Raw materials: These must be stated by name or formula Formula MUST be correct if name is not given Ignore incorrect formula if name is given Apply list principle if more than three materials given but Ignore any oxide of iron even if wrong Do NOT allow reagents which are only given in equations

Carbon or coke but NOT coal (1) Limestone but NOT lime (1) Air / oxygen but NOT “O” on its own (1)

Role: Oxygen (reacts with carbon) to produce high temperature/ heat or energy or exothermic (1) but NOT oxygen is an oxidising agent C + O

2 → CO

2 (1) Not C + CO

2 → 2CO Not 2 C + O

2 → 2 CO

Carbon or CO is a reducing agent (or makes CO) (1) 2Fe

2O

3 + 3C → 4Fe + 3CO

2 etc (1)

Allow equation with FeO; Fe2O

3 or Fe

3O

4

OR C + CO2 → 2CO

Lime stone forms slag (Calcium silicate) or reacts with SiO2 (Sand)

or with impurities (1) CaCO

3 → CaO +CO

2 (1)

CaO +SiO2 → CaSiO

3 (1)

OR CaCO3 + SiO

2 → CaSiO

3 +CO

2 scores (2) or zero if wrong

Zero if wrong metal given Ignore incorrect equations in THIS section

10

(b) Removal: Sulphur, Magnesium (or Calcium) (powder) added (1) or in an equation

even if incorrect Carbon; oxygen (1) (but NOT air allow if air penalised above) Blown into (or over) molten iron (1) Phosphorus; CaO or lime added or limestone (1)

Ignore incorrect oxides formed by P with Oxygen

Sulphur: Removed before C as oxygen would form SO2 (1)

SO2 is toxic or causes acid rain (Or a stated effect) (1)

OR S cannot be removed by oxygen (1) as iron is oxidised in preference (1)

6

Page 3 of 37

(c) (i) Iron: less ore extracted, OR less holes in the ground, OR to conserve resources of C and Fe, OR less unsightly landfill, OR Less greenhouse gas formed, OR less acidic / toxic gas evolved, OR less energy needed (1)

Not economic factors Only allow “by-product answers” if qualified by a “problem” If several answers given allow

Iron is magnetic (1)

(ii) Aluminium: Extraction needs a large (cost) amount of electricity or electrolysis (1) Collection of cans OR cost of melting, OR cost of sorting, OR cost of transport.(1)

NOT cost of removing “other substances: from cans” 4

[20]

M3. (a) (TiO2) treated with Cl

2 (1)

and C (coke) (1) Note, if other incorrect reagent mentioned lose one mark for each wrong reagent after 2 marks scored up to -2

at high temperature (1) If specific temperature mentioned allow between 500 to 1000 °C

TiCl4 formed (1)

TiO2 + 2C + 2Cl

2 → TiCl

4 + 2CO (1)

Note, equation can also score C, Cl2 and TiCl

4 marks

Or TiO2 + C +2 Cl

2 → TiCl

4 + CO

2

(TiCl4 react with) Na or (Mg) (1)

under argon (1) TiCl

4 + 4Na → 4NaCl +Ti (1)

Note this equation also scores the Na mark

Energy for TiO2 conversion into TiCl

4 expensive (1)

Raw materials in reduction of TiCl4 expensive (or Na or Cl

2 expensive) (1)

Precautions to keep TiCl4 dry (or prevent hydrolysis) expensive (1)

Batch process (expensive) (1) max 11

Page 4 of 37

(b) (In blast furnace) add limestone (or CaCO3) (1)

CaCO3 → CaO + CO

2 (1)

SiO2 + CaO → CaSiO

3 (1)

or 2 marks for combined equation CaCO3 + SiO

2 → CaSiO

3 + CO

2

Limestone mark can be scored in an equation

Forms slag (1)

In BOS converter main impurities in irono are: C (1) P (1) S (1)

Note that these marks can be scored in the equations

S removed using Mg (1) Mg + S → MgS (1)

Oxygen (used to remove C, P) (1) air not allowed

C + O2 → CO

2 (1)

OR 2 C + O2 → 2 CO

P4 + 5O

2 → P

4O

10 (1)

OR 4 P + 5 O2 → 2 P

2O

5

Limestone (or CaO) added (1) Oxide converted into slag (1)

Or equation between P4O

10 and CaO scores both marks

Max 13

(c) Iron scrap must be separated from other metals etc (1) Using magnet (or using magnetic properties) (1) It is then melted down (to convert it into steel) (1) And also used in BOS process (1) Use of scrap requires less energy than extraction (1) Because has higher iron content than ore OR scrap does not deplete native ore reserves (1) Scrap removed from countryside (1) (or any environmental issue e.g. mining but not greenhouse effect) Less CO

2 released into atmosphere (hence greenhouse effect)

(compared with extraction) (1) Max 6

[30]

Page 5 of 37

M4. (a) Reducing agent 1: C(1) (or coke)

Not coal

Equation: 3C + Fe2O

3 → 3CO + 2Fe (1)

or + 2Fe2O

3 → 3CO

2 + 4Fe

C + O2 → CO

2

C + ½ O2 →CO

CO2 + C → 2CO

penalise Fe2

(allow Fe3O

4 and FeO)

Reducing agent 2: CO (1)

Equation: 3CO + Fe2O

3 → 3CO

2 + 2Fe (1)

(again allow Fe3O

4, FeO)

Equation mark depends on correct reducing agent, but allow coal 4

(b) Equation 1: TiO2 + 2C + Cl

2 → TiCl

4 + 2CO

(1) C + Cl2

(1) balance or + C → CO

2

Equation 2: TiCl4 + 4Na (or 2Mg) → 4NaCl (or 2MgCl

2) + Ti

(1) for Na with TiCl4 or Mg

(1) for balance 4

(c) Extraction: form metal oxide (1) Or metal oxide implied

reduce or react with suitable reducing agent (1) Consequential on formation of metal oxide

Pollution problems: SO2 (1) or oxides of S not SO

3 alone

(allow any sensible and correct reducing agent identified)

any mention of acid rain or H

2SO

4

or erosion caused by acid rain or correct problem due to acid rain (1)

4 [12]

Page 6 of 37

M5. (i) Extraction by C reduction of oxide Iron (1)

Fe2O

3 + 3CO → 2Fe + 3CO

2 (1)

Extraction by electrolysis Aluminium (1)

Al3+ + 3e– → Al (1)

Extraction by metal displacement Titanium (1)

TiCl4 + 4Na → Ti + 4NaCl

or TiCl4 + 2Mg → Ti + 2MgCl

2 (1)

6

(ii) The reactive metal must first be extracted (1)

This extraction will require a great deal of energy or electrolysis (1) 2

(iii) Be2C + 4H

2O → 2Be(OH)

2 + CH

4

Species (1) Balanced (1)

2 [10]

M6. (a) Limestone (or CaCO3)

1

Removes SiO2

1

CaCO3 → CaO + CO

2

1

CaO + SiO2 → CaSiO

3

1

Removed as slag 1

Carbon 1

Removed with oxygen 1

2C + O2 →2CO (or C + O

2 → CO

2)

1

Page 7 of 37

(b) Dissolve in molten cryolite 1

Electrolyse 1

Carbon electrodes 1

Al3+ + 3e– → Al

1

2O2– → O2 + 4e–

1

Consumes less energy which is expensive 1

Separation of pure aluminium from scrap (or collection) costs 1

[15]

M7. (a) (i) C + CO2 → 2CO

(or 2C + O2 → 2CO, or carbon reduction of an iron oxide)

1

(ii) 3CO + Fe2O

3 →3CO

2 + 2Fe

1

(iii) CO is gaseous (or C is solid) 1

CO has more collisions (or C has very few collisions) 1

(b) Titanium carbide is stable. 1

Page 8 of 37

(c) (i) Basic oxygen process (or BOS) 1

(ii) Mg + S → MgS 1

(iii) React with oxygen 1

Forms phosphorus oxide (or P4O

10)

1

Removed as slag (or phosphate) (with CaO) 1

(iv) Any two from the following: saves energy, removes scrap from environment, uses fewer raw materials, fewer green house gases released, less CO released, less SO

2 released, less mining,

has greater % of iron, correct economic argument etc 2

(d) Cost of chlorine or sodium (or Mg) or argon or batch process (cost is QL mark)

1

Mention of another of these 1

[14]

M8. (a) Electron donor; 1

(b) CO (or C); 1

3CO + Fe2O

3 → 3CO

2 + 2Fe (or correct equations with carbon);

1

(c) Na (or Mg); 1

Argon; 1

Na (or Mg or TiCl4) reacts with air (or oxygen or water)

( or impurities of O or N in Ti); 1

Page 9 of 37

(d) (i) cryolite; 1

Molten (or liquid or solution); 1

(ii) Al3+ + 3e– → Al;

1 [9]

M9. (a) energy comes from combustion of coke/ C

(not coal) (allow this mark if stated that the C + O

2 → CO

2 reaction is

exothermic) 1

air blown in (not oxygen) 1

C + O2 → CO

2

1

CO2 + C → 2CO

1

Fe2 O

3 (1) + 3CO → 2Fe + 3CO

2

1

the carbon dioxide released contributes to global warming (or CO is toxic) (or slag is an eyesore)

1

limestone is used to remove silicon dioxide / impurities 1

as slag (or stated under equation)

1

CaCO3 → CaO + CO

2

1

CaO + SiO2 → CaSiO

3

(combination of these two equations gains 2 marks) 1

Page 10 of 37

(b) oxygen 1

is blown into molten iron (QoL) 1

to give phosphorus oxides or P4O

10 or P

4 + 5O

2 → P

4O

10

1

lime or limestone removes phosphorus oxides 1

as slag (or 6CaO + P

4O

10 → 2Ca

3(PO

4)

2 scores the last two marks)

1 [15]

M10. (a) Batch process involves stopping and starting (1)

Energy lost when cools down after stopping or energy needed to heat up each time (1)

2

(b) Fe2O

3 + 3C → 2Fe + 3CO use of C or CO (1)

balance (1)

or Fe2O

3 + 3CO → 2Fe + 3CO

2

or 2Fe2O

3 + 3C → 4Fe + 3CO

2

2

(c) TiO2 +2C + 2Cl

2 à TiCl

4 + 2CO use of C and Cl

2 (1)

balance (1)

or TiO2 + C + 2Cl

2 → TiCl

4 + CO

2

TiCl4 + 4Na → Ti + 4NaCl use of Na or Mg (1)

or TiCl4 + 2Mg → Ti + 2MgCl

2 balance (1)

4

(d) Na (or Mg) is expensive or Cl2 is expensive (1)

1

(e) Expensive electricity needed in electrolysis (1) 1

[10]

Page 11 of 37

M11. (a) (i) 2CuCO3 + C → 2Cu + 3CO

2

1

(ii) Charcoal /carbon /C 1

(b) (i) Iron is more reactive / iron ore needs much more heat to extract the iron

1

Carbon monoxide 1

(c) stage 1: TiO2 + 2C + Cl

2 → TiCl

4 + 2CO

(C + Cl2 in incorrect equation gains 1 mark)

2

allow equations with + C → CO2

stage 2: TiCl4 + 4Na (or 2Mg) → 4NaCl (or 2MgCl

2) + Ti

(Na or Mg in unbalanced equation gains 1 mark) 2

(d) Extraction: form metal oxide Or metal oxide implied

1

reduce or react with suitable reducing agent Consequential on formation of metal oxide

1

Pollution problems: SO2 (1) or oxides of S not SO

3 alone

(allow any sensible and correct reducing agent identified) 1

any mention of acid rain or H

2SO

4

or erosion caused by acid rain or correct problem due to acid rain

1 [12]

M12. (a) (i) 2C + O2 → 2CO

OR C + CO

2 → 2CO

Or multiples. Ignore state symbols.

1

Page 12 of 37

(ii) Fe2O

3 + 3CO → 2Fe + 3CO

2

Or multiples Penalise FE and Fe

2

Ignore state symbols 1

(iii) Economic:

• Scrap iron/steel has higher iron content.

• Recycling involves lower energy consumption

• Blast furnace not required Ignore cost Assume that “it” means recycling for both reasons

1

Environmental:

• Reduces greenhouse gas / CO2 / SO

2 emission.

• Reduces acid rain

• Reduces mining

• Reduces landfill

• Removes an eyesore 1

(b) (i) M1 Use of Cl2 and C

M2 Balanced equation consequential on correct reactants

EITHER

TiO2 + 2Cl

2 + 2C → TiCl

4 + 2CO

OR

TiO2 + 2Cl

2 + C → TiCl

4 + CO

2

Or multiples Ignore state symbols

2

Page 13 of 37

(ii) M1 Use of Na OR Mg

M2 Balanced equation consequential on correct reactants

EITHER

TiCl4 + 4Na → Ti + 4NaCl

OR

TiCl4 + 2Mg → Ti + 2MgCl

2


2

(iii) One from

• TiC / carbide is produced

• Product is brittle

• Product is a poor engineering material 1

(c) (i) One from

To allow

• ions to move

• current to flow

• it to conduct electricity 1

(ii) 2O2– → O2 + 4e–

Or multiples including

3O2– → 1.5 O2 + 6e–

Ignore state symbols Ignore charge on the electron Credit the electron being subtracted on the LHS

1

(iii) Carbon / graphite / the electrodes oxidise OR Carbon / graphite / the electrodes burn in / react with the oxygen formed OR carbon dioxide / CO

2 is formed

1

Page 14 of 37

(iv) Recycling involves lower electricity OR less energy consumption OR The converse for electrolysis

Ignore references to raw materials Assume that “it” means recycling The answer MUST show some evidence of comparison e.g. lower or less

1 [13]

M13. (a) (i) M1 The enthalpy change / heat change at constant pressure when 1 mol of a compound / substance / product

1

M2 Is formed from its (constituent) elements 1

M3 With all reactants and products / all substances in standard states OR All reactants and products / all substances in normal states under standard conditions / 100 kPa / 1 bar and specified T / 298 K

Ignore reference to 1 atmosphere 1

(ii) By definition OR Because they are elements

1

(iii) M1 ΔHf = ΣΔH

f (products) – ΣΔH

f(reactants)

1

M2 = –1669 – 3(–558) (This also scores M1)

1

M3 = (+) 5 (kJ mol–1)

Correct answer gains full marks. Assume the value is positive unless specifically stated as negative. Credit 1 mark if – 5 (kJ mol–1). For other incorrect or incomplete answers, proceed as follows: • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either a correct cycle with 3BaO OR a clear statement of M1 which could be in words and scores only M1

1

Page 15 of 37

(b) (i) One from

• Aluminium is expensive (to extract OR due to electrolysis)

• High energy cost

• The cost of heating strongly This requires a clear statement about cost

1

(ii) One from

• increase collision frequency

• OR more collisions

• OR more chance of colliding The answer MUST refer to more collisions. Ignore “more available to collide”

1

(c) (i) Ba + 2H2O → Ba(OH)

2 + H

2

Ignore state symbols Allow multiples and correct ionic equations

1

(ii) M1 Ba2+ + SO4

2– → BaSO4

(or the ions together)

Allow crossed out Na+ ions, but penalise if not crossed out

1

M2 White precipitate / white solid

Ignore state symbols Ignore “milky”

1

(iii) M1 Barium meal or ( internal ) X-ray or to block X-rays 1

M2 BaSO4 / barium sulfate is insoluble (and therefore not toxic)

Accept a correct reference to M1 written in the explanation in M2, unless contradictory. For M2 NOT barium ions NOT barium NOT barium meal and NOT “It”. Ignore radio-tracing.

1 [14]

M14. (a) (i) 2CuFeS2 + 2SiO

2 + 4O

2 → Cu

2S + 2FeSiO

3 + 3SO

2

1

Page 16 of 37

(ii) Acid rain

OR

an effect either from acid rain or from an acidic gas in the atmosphere

1

(iii) SO2 could be used to make H

2SO

4

OR

to make gypsum/plaster or CaSO4 (xH

2O)

1

(b) Cu2S + 2O

2 → 2CuO + SO

2


1

(c) 2CuO + C → 2Cu + CO2

OR

CuO + C → Cu + CO Or multiples Ignore state symbols

1

(d) (i) Any one from the following two ONLY Apply the list principle

• (Scrap) iron is cheap

• Low energy requirement Not “less energy”

1

(ii) Fe + Cu2+ → Fe2+ + Cu


1 [7]

Page 17 of 37

M15. (a) (i) Reducing agent

OR

Reduce(s) (WO3/tungsten oxide)

OR

electron donor

OR

to remove oxygen (from WO3/tungsten oxide or to form water);

1

(ii) WO3 + 3H

2 → W + 3H

2O

Or multiples 1

(iii) One from

H2 is

• explosive

• flammable or inflammable

• easily ignited Ignore reference to pressure or temperature

1

(b) (i) Addition Ignore “electrophilic” Penalise “nucleophilic addition”

OR

(catalytic) hydrogenation

OR

Reduction 1

(ii) Geometric(al)

OR

cis/trans OR E Z OR E/Z 1

Page 18 of 37

(c) (i) (If any factor is changed which affects an equilibrium), the position of equilibrium will shift/move/change/respond/act so as to oppose the change.

OR

(When a system/reaction in equilibrium is disturbed), the equilibrium shifts/moves in a direction which tends to reduce the disturbance

A variety of wording will be seen here and the key part is the last phrase and must refer to movement of the equilibrium. QoL

1

(ii) M1 – Statement of number of moles/molecules There are more moles/molecules (of gas) on the left/of reactants

OR

fewer moles/molecules (of gas) on the right./products

OR

there are 4 moles/molecules (of gas) on the left and 2 moles/ molecules on the right.

Ignore “volumes” for M1 Mark independently

M2 – Explanation of response/movement in terms of pressure Increase in pressure is opposed (or words to that effect)

OR

pressure is lowered by a shift in the equilibrium (from left) to right/favours forward reaction.

2

Page 19 of 37

(d) ΣB(reactants) – ΣB(products) = ΔH (M1)

OR

Sum of bonds broken – Sum of bonds formed = ΔH (M1)

B(H–H) + ½B(O=O) – 2B(O–H) = – 242 (M1)

B(H–H) = – 242 – ½(+496) + 2(+463) (this scores M1 and M2)

B(H–H) = (+)436 (kJ mol–1) (M3)

Award 1 mark for – 436

Candidates may use a cycle and gain full marks. M1 could stand alone Award full marks for correct answer. Ignore units. Two marks can score with an arithmetic error in the working.

3 [11]

M16. (a) M1 The yield of zinc oxide increases/greater

If M1 is given as “decrease” OR “no effect” then CE= 0

M2 Removal of the carbon dioxide results in the equilibrium Either Shifting/moving/goes to the right shifting/moving/goes L to R favours the forward reaction/towards the products

M3 (By Le Chatelier’s principle) the reaction/equilibrium will respond so as to replace the CO

2/lost product

OR to make more CO2

OR to increase concentration of CO2

For M3, not simply “to oppose the change/to oppose the loss of CO

2/to oppose the removal of carbon dioxide.”

3

(b) M1 Process 2 produces/releases SO2

OR Process 2 produces/releases CO

M2 It/Process 3 avoids the release of SO2 OR CO

OR It/Process 3 (captures and) converts SO2 to H

2SO

4

M3 SO2 causes acid rain OR is toxic/poisonous

OR CO is toxic/poisonous 3

Ignore “global warming” and “greenhouse gases” and “the ozone layer” If both CO and SO

2 claimed to form acid rain, treat as contradiction

Page 20 of 37

(c) M1 Process 3 (is expensive because it) uses electrolysis OR due to high electricity/electrical consumption

M2 this is justified because the product/zinc is pure

Ignore “energy” Penalise “purer”

2

(d) M1 Zn2+ + 2e– Zn

Ignore state symbols

M2 the negative electrode OR the cathode

Ignore absence of negative charge on electron Accept electrons subtracted from RHS

2

(e) M1 The reaction of ZnO with sulfuric acid OR the second reaction in Extraction process 3

M2 neutralisation or acid-base

OR alternatively

M1 The reaction of zinc carbonate in Extraction process 1

M1 could be the equation written out in both cases

M2 (thermal) decomposition

M2 depends on correct M1

M3 It/carbon is oxidised/gains oxygen/changes oxidation state/number from 0 to +2/increase in oxidation state/number in Process 2

Do not forget to award this mark Ignore reference to electron loss but penalise electron gain Ignore “carbon is a reducing agent”

3

Page 21 of 37

(f) M1 Zn + H2O ZnO + H

2

M2 Zinc oxide and hydrogen

OR as an alternative

M1 Zn + 2H2O Zn(OH)

2 + H

2

M2 Zinc hydroxide and hydrogen

Mark independently If ZnO

2 is given for zinc oxide in the equation, penalise M1 and

mark on If ZnOH is given for zinc hydroxide in the equation, penalise M1 and mark on Ignore state symbols Credit multiples of the equation If M1 is blank, either of the M2 answers could score To gain both marks, the names must match the correct equation given.

2 [15]

M17. (a) Mg2+ + 2OH– Mg(OH)2

NOT multiples Ignore state symbols

1

(b) Mg(OH)2 + 2HCl MgCl

2 + 2H

2O

Or multiples or ionic, with or without the spectator ions Ignore state symbols Accept either of these two equations

OH– + H+ H2O

Mg2+ + 2Cl– MgCl2

1

(c) Mg2+ + 2e– Mg

Or multiples Ignore state symbols Credit electrons subtracted from RHS Ignore absence of charge on e

1

Page 22 of 37

(d) (i) M1 use of Cl2 and C

M2 balanced equation consequential on correct reactants

TiO2 + 2Cl

2 + 2C TiCl

4 + 2CO

OR

TiO2 + 2Cl

2 + C TiCl

4 + CO

2


2

(ii) TiCl4 + 2Mg Ti + 2MgCl

2


1

(iii) Reducing agent OR reduces TiCl4

OR

Electron donor Credit “reduction” or “reductant” Penalise “electron pair donor”

1

(e) M1 Hydrogen/H2 produced

OR an equation to produce hydrogen/H2

(eg Mg + 2H2O Mg(OH)

2 + H

2)

(eg Mg + H2O MgO + H

2)

M2 requires correct M1

risk of explosion OR forms explosive mixture (with air)

OR (highly) flammable For M1 Do not penalise an incorrect equation; the mark is for H

2 or

hydrogen Allow one mark only for “exothermic reaction with steam/H

2O” for a

candidate who has not scored M1 Ignore “violent” reaction

2 [9]

Page 23 of 37

M18. (a) MnO2 + 2CO Mn + 2CO

2


1

(b) Al Al 3+ + 3e–

Or multiples Ignore state symbols Credit electrons subtracted from LHS Ignore absence of charge on e

1

(c) 2CuO + C 2Cu + CO2

OR

CuO + C Cu + CO Or multiples Ignore state symbols

1

(d) (i) Any one from the following three ONLY

• Low(er) energy requirement

• Low(er) temperature

• Copper is obtained from low grade ore Apply the list principle

1

(ii) Fe + Cu2+ Fe2+ + Cu


1 [5]

M19. (a) (i) 2MoS2 + 7O

2 → 2MoO

3 + 4SO

2

OR

Allow multiples Ignore state symbols

1

MoS2 + 3 O

2 → MoO

3 + 2SO

2

Page 24 of 37

(ii) M1 Environmental problem

Acid rain

OR

An effect either from acid rain or from an acidic gas in the atmosphere.

M2 Use

SO2 could be used to make / to form / to produce

(or wtte) H2SO

4 / sulfuric acid

OR

To make / to form / to produce (or wtte) gypsum / CaSO4

or plaster of Paris / plaster board Ignore references to the greenhouse effect Penalise reference to the ozone layer using the list principle

2

(iii) MoO3 + 3H

2 → Mo + 3H

2O


1

(iv) One from

H2 is

• Explosive

• (in)flammable

• easily ignited Ignore “burns”

1

(b) (i) To allow ions to move (when molten)

OR

Ions cannot move in the solid 1

(ii) Ca2+ + 2e- Ca

Or multiples Ignore state symbols Ignore charge on the electron unless incorrect and accept loss of two electrons on the RHS

1

→

Page 25 of 37

(iii) (High) electricity / electrical energy (cost) Ignore “energy” and ignore “current”

[8]

M20. (a) One from

• Ti is not produced

• TiC / carbide is produced OR titanium reacts with carbon

• Product is brittle

• Product is a poor engineering material Penalise “titanium carbonate”

Ignore “impure titanium”

Credit “titanium is brittle” 1

(b) Heat (energy) change at constant pressure QoL

1

(c) The enthalpy change in a reaction is independent of the route taken (and depends only on the initial and final states)

Credit “heat change at constant pressure” as an alternative to “enthalpy change”

1

(d) M1 The enthalpy change / heat change at constant pressure when 1 mol of a compound / substance / product

For M1, credit correct reference to molecule/s or atom/s

M2 is formed from its (constituent) elements

M3 with all reactants and products / all substances in standard states

OR all reactants and products / all substances in normal states under standard conditions / 100 kPa / 1 bar and any specified T (usually 298 K)

Ignore reference to 1 atmosphere 3

(e) (i) Na / it is not in its standard state / normal state under standard conditions

OR

Standard state / normal state under standard conditions for Na is solid / (s)

QoL Ignore “sodium is a liquid or sodium is not a solid”

1

Page 26 of 37

(ii) M1 ∆Hr = ∑∆H

f (products) - ∑∆H

f (reactants)

M2 ∆Hr = 4(−411) − (−720) − 4(+3)

= −1644 + 720 − 12 (This also scores M1)

M3 = −936 (kJ mol−1)

Correct answer gains full marks

Credit 1 mark for + 936 (kJ mol−1)

Credit 1 mark for – 924 (kJ mol−1)

i.e. assuming value for Na(l) = 0 For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either a correct cycle with 2Cl

2 and 4Na OR a clear complete

statement of M1 which could be in words and scores only M1

3

(iii) Reducing agent Ignore “reduces titanium”

OR reductant OR reduces TiCl4

OR electron donor 1

[7]

M21. (a) (i) reduction OR reduced OR redox OR reduction–oxidation

Not “oxidation” alone 1

Ignore state symbols Do not penalise absence of charge on electron

Credit Fe3+ Fe – 3e–

Credit multiples 1

(ii) Fe3+ + 3e–

Fe

Page 27 of 37

(b) (i) Because (one of the following)

CO is not the only product OR Reference to “incomplete combustion to form CO” does not answer the question

(Some) complete combustion (also)occurs OR

CO2 is (also) formed

Further oxidation occurs 1

(ii) The enthalpy change / heat (energy) change at constant pressure in a reaction is independent of the route / path taken (and depends only on the initial and final states)

1

(iii) M1 The enthalpy change / heat change at constant pressure when 1 mol of a compound / substance / element For M1, credit correct reference to molecule/s or atom/s

M2 is burned completely / undergoes complete combustion in (excess) oxygen

M3 with all reactants and products / all substances in standard states

For M3 Ignore reference to 1 atmosphere

OR all reactants and products / all substances in normal / specified states under standard conditions / 100 kPa / 1 bar and specified T / 298 K

3

Page 28 of 37

(c) M1 (could be scored by a correct mathematical expression which must have all ∆H symbols and the ∑)


Credit 1 mark ONLY for –1 (kJ mol–1)

M1 ∆Hr = ∑∆H

f (products) – ∑∆H

f (reactants)

Credit 1 mark ONLY for – 27 (kJ mol–1) i.e. assuming value for Fe(l) = 0

OR correct cycle of balanced equations with 2Fe, 3C and 3O2

M2 ∆Hr = 2(+14) + 3(– 394) – (– 822) – 3(–111)

= 28 –1182 + 822 + 333

(This also scores M1)

M3 = (+) 1 (kJ mol–1)

(Award 1 mark ONLY for – 1)

(Award 1 mark ONLY for – 27) For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a

transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2)

• If no AE, check for a correct method; this requires either a correct cycle with 2Fe, 3C and 3O

2 OR a clear statement of

M1 which could be in words and scores only M1 3

(d) (i) C(s) + O2(g) CO

2(g)

State symbols essential Possible to include C(s, graphite)

1

(ii) These two enthalpy changes are for the same reaction / same equation / same reactants and products

Penalise reference to CO2 being produced by a different route

OR

They both make one mole of carbon dioxide only from carbon and oxygen (or this idea clearly implied)

“both form CO2” is not sufficient (since other products might occur

e.g.CO)

OR

The same number and same type of bonds are broken and formed 1

[12]

Page 29 of 37

M22. (a) (i) SiO2 + 2Cl

2 + 2C SiCl

4 + 2CO

Ignore state symbols Credit multiples of either equation

OR

SiO2 + 2Cl

2 + C SiCl

4 + CO

2

1

(ii) (fractional) distillation

OR

G(L)C or gas (–liquid–) chromatography 1

(b) (i) SiCl4 + 2H

2 Si + 4HCl

Ignore state symbols Credit multiples Penalise ionic HCl

1

(ii) Reducing agent / reductant / reduces SiCl4 / reduces (silicon) / electron

donor 1

(iii) Explosion / explosive

OR

(highly) flammable / inflammable

OR

readily / easily ignites / burns / combusts 1

(c)

Ignore state symbols Credit multiples

1 [6]

2MgO + Si 2Mg + SiO2

Page 30 of 37

M23. (a) Ti is not produced

OR

TiC / carbide is produced OR titanium reacts with carbon

OR

Product is brittle

OR

Product is a poor engineering material Penalise “titanium carbonate” Ignore “impure titanium” Credit “it / titanium is brittle”

1

(b) (i) FeTiO3 + 3½Cl

2+ 3C FeCl

3 + TiCl

4 + 3CO

Ignore state symbols Credit multiples

1

(ii) FeCl3+ TiCl

4 + 7Na 7NaCl + Fe + Ti

OR (for example)

2FeCl3 + TiCl

4 + 10Na 10NaCl + 2Fe + Ti

Ignore state symbols Credit multiples including ratios other than 1:1 Ignore working

1

(c) Either order Penalise reference to incorrect number of electrons in M1

M1 The Cu2+ / copper(II) ions / they have gained (two) electrons

OR Cu2+ + 2e– Cu

For M1, accept “copper” if supported by correct half-equation or simplest ionic equation

OR oxidation state / number decreases (or specified from 2 to 0) Ignore charge on the electron

M2 The Cu2+ / copper(II) ions / they have been reduced

For M2 do not accept “copper” alone 2

Page 31 of 37

(d) 2O2– O2 + 4e–

Or multiples including

3O2- 1.5 O2 + 6e-

Ignore state symbols Ignore charge on the electron Credit the electrons being subtracted on the LHS

1 [6]

M24. (a) (i) M1 (could be scored by a correct mathematical expression which must have all ΔH symbols and the ⅀⅀⅀⅀ or SUM)


Credit 1 mark ONLY if –122 (kJ mol−1)

M1 ΔH = ⅀ΔHf (products) - ⅀ΔH

f (reactants)

OR a correct cycle of balanced equations

M2 ΔH = 3(−394) − 3(−111) − (−971) (This also scores M1)

M3 = (+) 122(kJ mol−1)

Award 1 mark ONLY for –122

For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for correct method; this requires either a correct cycle of balanced equations OR a clear statement of M1 which could be in words and scores M1 only

3

(ii) By definition Ignore reference to “standard state”

OR

Because it is an element / elemental 1

Page 32 of 37

(b) (i) TiO2 + 2Cl

2 + 2C

Allow multiples

OR

TiO2 + 2Cl

2 + C


M1 use of Cl2 and C

M2 a correct balanced equation 2

(ii) TiCl4 + 4Na

Allow multiples

OR

TiCl4 + 2Mg


M1 use of Na OR Mg

M2 a correct balanced equation 2

(c) (i) 4 FeCr2O

4 + 8 Na

2CO

3 + 7O

2


1

(ii) Cr2O

3 + 2Al


1 [10]

TiCl4 + 2CO

TiCl4CO

2

Ti + 4NaCl

Ti + 2MgCl2

8Na2CrO

4 + 2Fe

2O

3 + 8CO

2

Al2O

3 + 2Cr

Page 33 of 37

M25. (a) M1 (could be scored by a correct mathematical expression

Correct answer to the calculation gains all of M1, M2 and M3

M1 ΔH = ΣΔHf (products) − ΣΔH

f (reactants)

Credit 1 mark for − 101 (kJ mol−1)

OR a correct cycle of balanced equations

M2 = − 1669 − 3(− 590) = − 1669 + 1770 (This also scores M1)

M3 = + 101 (kJ mol−1)

Award 1 mark ONLY for − − − − 101

For other incorrect or incomplete answers, proceed as follows • check for an arithmetic error (AE), which is either a transposition error or an incorrect multiplication; this would score 2 marks (M1 and M2) • If no AE, check for a correct method; this requires either a correct cycle with 3Sr and 2Al OR a clear statement of M1 which could be in words and scores only M1

M4 - Using powders Any one from

• To increase collision frequency / collisions in a given time / rate of collisions

• To increase the surface contact / contact between the solids / contact between (exposed) particles

Ignore dividing final answer by 3 Penalise M4 for reference to molecules.

5

M5 Major reason for expense of extraction Any one from

• Aluminium is extracted by electrolysis OR aluminium extraction uses (large amounts of) electricity

• Reaction / process / It / the mixture requires heat

• It is endothermic

Page 34 of 37

(b) Calcium has a higher melting point than strontium, because Ignore general Group 2 statements.

Correct reference to size of cations / proximity of electrons M1 (For Ca) delocalised electrons closer to cations / positive ions / atoms / nucleus OR cations / positive ions / atoms are smaller OR cation / positive ion / atom or it has fewer (electron) shells / levels

Penalise M1 if either of Ca or Sr is said to have more or less delocalised electrons OR the same nuclear charge. Ignore reference to shielding.

Relative strength of metallic bonding M2 (Ca) has stronger attraction between the cations / positive ions / atoms / nucleus and the delocalised electrons OR stronger metallic bonding

(assume argument refers to Ca but credit converse argument for Sr) CE= 0 for reference to molecules or Van der Waals forces or intermolecular forces or covalent bonds.

2

(c) M1 2Mg + O2 2MgO

M2 Mg + 2H2O Mg(OH)

2 + H

2

Credit multiples of the equations.

M3 Magnesium hydroxide is used as an antacid / relieve indigestion (heartburn) / neutralise (stomach) acidity / laxative

Not simply “milk of magnesia” in M3 3

[10]

M26. (a) (i) 3CuS(s) + 8HNO3(aq) 3CuSO

4(aq) + 8NO(g) + 4H

2O(l)

1

(ii) (+) 5 (+) 2

2

(iii) 4H+ + NO3

− + 3e− 2H2O + NO

Ignore state symbols. Credit multiples of this equation only. Ignore absence of charge on the electron.

1

(iv) S2− + 4H2O SO 4

2− + 8e− + 8H+

Ignore state symbols. Credit multiples of this equation only. Ignore absence of charge on the electron.

1

Page 35 of 37

(b) M1 add scrap / recycled / waste iron (or steel) to the aqueous solution If M1 refers to iron / steel, but does not make it clear in the text that it is “scrap” / “waste” / “recycled”, penalise M1 but mark on.

M2 the iron is a more reactive metal OR Fe is a better reducing agent Credit zinc or magnesium as an alternative to iron for M2, M3 and M4 only, penalising M1

M3 Cu2+ / copper ions are reduced / gain electrons

OR Cu2+ + 2e− Cu

OR copper / Cu is displaced by Fe Ignore absence of charge on the electron.

M4 Fe + Cu 2+ Fe 2+ + Cu ONLY

For M4, ignore state symbols 4

[9]

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Page 37 of 37

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