Chemical Changes Part 3 Mark schemes

Q1.

(a) (i) mix (owtte)

accept to allow more collisions / helps particles to collide (owtte)

idea of more efficient heat transfer

do not allow heat is a catalyst

1

(ii) higher and more

1

powder and big

1

concentrated and more

1

(b) electrons

1

(c) H+

1

[6]

Q2.

(a)

accept dots / crosses / e

must be drawn on diagram

electrons do not need to be paired

ignore brackets or + or -charges

ignore 2,8,7

1

(b) (one) electron

recognition that electrons are involved

1

lost / given away / transferred from sodium / transferred to chlorine owtte

must be linked to electrons

accept loses electron(s) for 2 marks

NB loses 2 or more electrons gains 1 mark

reference to sharing / covalent max 1 mark

ignore charges on ions formed

1

(c) (i) any one from:

• ions / atoms / they are / it is negatively charged / anions

accept they are negative

• opposite (charges) attract

accept they are attracted or it is oppositely charged

ignore opposite forces attract

1

(ii) hydrogen

accept H2

ignore H or H+

1

(d) (i) poisons released into environment (owtte)

accept any sensible idea of harm / harmful / poisons / poisonous / pollution / damaging

do not accept answers such as global warming / ozone layer etc.

ignore safety unless qualified

1

(ii) any one sensible idea eg

• loss of work / unemployment

eg shops / house prices etc.

or

company goes out of business

• any adverse effect on local economy (owtte)

• any adverse effect on paper production / cost of paper / cost of water (treatment)

allow less expensive to use chlorine or converse

• chlorine (compounds) have been used (for many years) without

causing harm owtte

• only a tiny amount of chlorine is released so it would not cause harm

ignore uses of chlorine to treat drinking water unless qualified

1

(iii) ideas related to bias

accept more reliable or valid or fair

ignore more accurate / fair test

1

[8]

Q3.

(a) gas / g

accept low density / low boiling point

or weak intermolecular forces or

small molecules or simple molecules

or simple molecular (structure)

accept volatile or easy to evaporate

ignore very light

ignore incorrect name of gas

1

(b) filter / filtration

accept filter paper

accept decant / centrifuge

ignore filter funnel / sieving / drained off / funnelling

ignore names of compounds

ignore evaporation / heating if after filtration

do not accept crystallisation

1

(c) evaporation / crystallisation

accept heating / boiling

accept ‘leave for a few days’ owtte

allow cool

do not allow freeze

ignore filtration

1

(d) candidates can gain marks from any two of the three linked pairs

hydrogen chloride escaped / released (into atmosphere) or (hydrogen chloride)

damaged vegetation / harmful

used to make chlorine / bleach

to get both of these 2 marks hydrogen chloride must be mentioned

ignore HCl formed / produced / made

ignore sale of hydrogen chloride

1

unpleasant smell (of calcium sulfide)

or

waste of calcium (sulfide)

converted to sulfur

or

used to make sulfuric acid

ignore calcium sulfide alone

allow calcium / calcium sulfate for calcium sulfide

to get both of these 2 marks calcium (sulfide) must be mentioned

ignore sale of calcium sulfide

1

unreacted coal (1)

recycled / burnt / used / sold (1)

must be linked to first coal point

1

[7]

Q4.

(a) burette

1

(b) indicator changed colour

allow any indication of colour change

1

(c) (i) 0.2 or 18.3 to 18.5

1

(ii) 18.4

1

(iii) improve reliability

allow improve accuracy

allow to calculate a mean / average

or get rid of anomalous result

ignore fair test / correct results / random results

1

[5]

Q5.

(a) hydroxide (ion) / OH– / OH–(aq)

ignore OH

1

(b) fully / all / completely ionised / dissociated

ignore strongly ionised or more ions or concentration

ignore all ‘noise’

do not accept ions are fully ionised / dissociated

1

(c) assume it = sodium hydroxide

any valid test

incorrect test / titration = 0 marks for question

1

linked comparison

correct result / reference to pH with no test = 1 mark

eg UI or full range indicator or pH

paper / solution / (pH) meter (1)

NaOH has higher pH or

allow converse for weak(er)

pH values must be above 7

correct comparison of colours (1)

NaOH – purple, Ammonia – blue

allow correct comparison of blue or purple

or

conductivity test (1)

NaOH conducts better / more or bulb brighter (1)

1

[4]

Q6.

(a) (i) C

must be correct symbol

do not accept carbon

any balancing must be correct

1

(ii) Fe + CO2

correct formulae

1

2... . + 3... .

correct balancing

allow Fe2 + 3CO2 for this mark

1

(iii) layers / atoms in pure iron are able to slide over each other

it = pure iron

accept ions for atoms

ignore molecules / particles

or

layers / atoms in cast iron are unable to slide over each other (easily)

1

(b) any three from:

mention of ozone = max 2

• less iron ore used

accept the idea that ores would be conserved but not unspecified conservation

• less other metals extracted / used to make different steels

accept the idea that ores would be conserved but not unspecified conservation

• less fuel used

accept the idea that fuels would be conserved

ignore reduces energy requirements

• less specified pollution

accept global warming / greenhouse effect / CO2 / CO / carbon emissions / acid rain / SO2 / global dimming /

do not accept ozone layer

• less / no landfill space needed

ignore reduces waste

• less / no mining needed or fewer specified effects of mining

accept effect such as eyesore / loss of habitat

eg ‘less mining iron ore’ = 2 marks

3

[7]

Q7.

(a) (i) (different) properties

allow ideas of different property / behaviour / element

1

(ii) any one from:

they = Crawford + Cruikshank

• they had high status

or

they were lecturers / doctors / professors / famous scientists

• other scientists repeated experiments

allow experiment could be repeated

allow other scientists showed they had different properties

• they had proof

or

lots of / strong / conclusive / enough / clear evidence

ignore evidence unqualified

1

(iii) other scientists obtained similar results / proved it

or

experiments were repeated

1

(b) (i) any one from:

• mass of solid / strontium (chloride) / barium (chloride)

allow amount / volume

• volume of water

allow amount / mass

• type of container

allow initial / starting temperature (of water)

ignore room temperature / time / concentration

ignore reference to hydrochloric acid

1

(ii) 2 and takes in heat / energy

or

2 and temperature goes down (owtte)

1

(iii) temperature increased for one experiment and decreased for the other (owtte)

or

one was exothermic and one was endothermic (owtte)

accept experiment 1 was exothermic

1

(c) any one from

• positive / + (charge)

do not accept incorrect further qualification eg electrons / atoms / electrodes

• opposite (charges) attract

1

[7]

Q8.

(a) (i) H+

1

(ii) OH–

1

(iii) lower than

1

(b) with HCl:

UI goes red / pink

allow a comparison eg redder than ethanoic acid

1

has a pH 0 ,1 ,2 or 3

allow a comparison eg has pH less than ethanoic acid.

do not accept an incorrect pH.

or

with ethanoic acid:

UI goes orange / yellow (1)

allow a comparison with HCl

has a pH 4 / or above (but less than 7) (1)

allow a comparison with HCl

1

(c) completely

1

(d) (i) conical flask

1

(ii) titration

1

(iii) repeat

allow compare with another students results

or

take average

1

[9]

Q9.

(a) atoms

1

(b) mixture

1

metal

1

structure

1

smart

1

(c) (i) any two from:

• saves raw materials / iron ore

• saves energy / fuels

accept cheaper / saves money

• make new / useful items

• make money / it is economic

• reduces pollution

allow less harmful for the environment

• decreases cost of steel cans

• reduces carbon dioxide emissions

• decreases waste materials / use of landfill

2

(ii) any one from:

• provide information / education of the need to recycle

• legislate against / charge for waste

• reward / pay people to recycle

accept fine people for not recycling

• put labels on the cans

• provide recycling bags / bins / areas

1

[8]

Q10.

(a) positive

accept + or +ve or plus

1

(b) chlorine

1

(c) (i) hydroxide

Any indication of hydro…

1

(ii) destroys / damages / dissolves (owtte) the hair / follicle / root

allow burns / reacts with the hair

ignore incorrect name of compound

1

[4]

Q11.

(a) any two from:

• outer shell electrons / electrons in

highest energy level (in metals)

• electrons are delocalised / sea of electrons

• electrons are free or electrons move around

or electrons are free to flow or electrons

attracted to positive terminal

• electrons carry charge / current or electrons

form the current / electrons transfer charge / electrons

pass charge

ignore electrons carry electricity

ignore reference to positively charged atoms / ions

if they state electrons have +ve charge = max 1 mark

if they state covalent bonding then max 1 mark

2

(b) ions can move / are attracted to electrode

accept ions are free

allow ‘they’ for ions

or

attracted to named electrode

or

ions are charged or ions form / carry

the current or ions form the charge

1

(c) (i) electron gain

ignore hydrogen reduces charge

1

(ii) sodium hydroxide or NaOH or caustic soda

do not allow hydroxide alone

1

(iii) 2Cl– ─ 2 e– → Cl2

or

2Cl– → Cl2 + 2 e–

allow fractions or multiples

allow e or e–

do not allow e+

1

[6]

Q12.

(a) water / H2O / hydrogen oxide

1

(b) eg H (atom) loses an electron to form H+

or only a proton left

1

(c) is partially ionised in water

1

(d) (i) eg same concentration / quantity of Mg

accept: volume of acid / ribbon for both / same time

accept: volume of gas measured under the same conditions

1

(ii) C A D B

1

(e) (i) OH–

1

(ii) acidic

1

[7]

Q13.

(a) conducts (electricity) or

accept flexible

allows electrons / current to flow

ignore conducts heat

1

(b) electron

1

(c) (i) lithium>copper>tungsten or

Li>Cu>W

all correct

allow 1 mark for one metal in the correct position

2

(ii) has high / highest melting point

accept has high / highest boiling point

or

can withstand the highest temperature

1

(d) unreactive

1

[6]

Q14.

(a) (i) many ethene / molecules / monomers

accept double bonds open / break

1

join to form a long hydrocarbon / chain / large molecule

accept addition polymerisation

ignore references to ethane

correct equation gains 2 marks

1

(ii) (can be deformed but) return to their original shape (when

heated or cooled)

ignore ‘it remembers its shape’

1

(iii) cross links / extra bonds in PEX

accept inter-molecular bonds

ignore inter-molecular forces

1

molecules / chains in PEX are held in position

accept rigid structure

1

molecules / chains in PEX unable to slide past each other / move

it = PEX throughout

1

(b) any four from:

• less (hydrocarbon) fuels used

allow less energy

• less / no electrical energy used

allow no electrolysis

• reduce carbon / carbon dioxide emissions

allow less global warming

• reduce / no pollution by sulfur dioxide / acid rain

• continuous process

allow less / no transportation

• conserve copper which is running out or only low-grade ores available

• reduce the amount of solid waste rock that needs to be disposed

allow less waste

• reduce the need to dig large holes (to extract copper ores)

allow less mining

ignore costs / sustainability / non-renewable

4

[10]

Q15.

(a) covalent

1

(b) (i) liquid

1

(ii) fluorine

accept F / F2

do not accept fluoride

1

(c) (i) should fluoride ions be added to drinking water?

1

(ii) any one from:

• not enough reliable/valid evidence

• may be other factors involved

• it is an opinion / choice / belief / ethics issue

• it can’t be scientifically investigated

allow can’t do an experiment

ignore test

mark independently of (c) (i)

1

[5]

Q16.

(a) hydrogen / H+ /2H+ / H3O+

allow H / 2H

do not accept H2

apply list principle

1

(b) (i) 143

correct answer with or without working = 2 marks

ignore units

if answer is not correct

40 + (2 × 35.5) + (2 × 16) gains 1 mark

2

(ii) 49.7% (49.6 to 50)

correct answer with or without working = 2 marks

answer 49 gains 1 mark

if answer is not correct:

(71 ÷ 143) × 100 gains 1 mark

allow error carried forward from part (b)(i)

ie. (71 or their (2 × 35.5) ÷ answer to (b)(i)) × 100 gains 2 marks if calculated correctly and 1 mark if not calculated correctly.

Special case 35.5 ÷ 143 × 100 = 24.8

to 25% or 35.5 ÷ answer to (b)(i) × 100 correctly calculated for 1 mark

2

(iii) 9.9 to 10g

allow ecf from (b)(i) or (b)(ii)

1

(c) (i) an alkali

apply list principle

accept named alkali

accept hydroxide

accept soluble base

ignore base

1

(ii) a solid / insoluble substance (owtte)

1

(iii) filter / filtration

allow decant / centrifuge

accept filtration followed by evaporation or filtration and evaporation

do not accept filtration or evaporation

do not accept evaporation and filtration

1

[9]

Q17.

(a) (i) any one from:

• they are positive / cations

• they are H+

• opposite charges attract

ignore atom

1

(ii) potassium is more reactive (or reverse)

assume ‘it’ refers to hydrogen

allow potassium reacts with water

allow potassium is very reactive or most reactive metal / element

allow hydrogen gains electrons more easily / is reduced more easily

accept potassium is higher up the reactivity series

1

(b) 6 and 2

accept correct multiples and fractions

1

(c) (i) the reaction / it is reversible or a description of a reversible reaction

allow ‘it is an equilibrium’

allow reversible symbol drawn correctly

allow ‘the reverse / back reaction’

1

(ii) lithium nitride

assume that ‘it’ or if they do not specify means lithium nitride

assume lithium / lithium nitrate refers to lithium nitride

• hydrogen is bonded / held / absorbed / has formed a

compound / reacted with lithium nitride

1

plus one of:

• does not explode / cause a fire

• is not free / less hydrogen

• is not under pressure

• does not leak

• is only released slowly

1

• compound of hydrogen with lithium nitride / product is

(more) stable / less reactive / less chance of a reaction

accept converse for hydrogen as below

assume that gas / hydrogen means gas in the cylinder

• hydrogen (in cylinder) / gas is not bonded / held

absorbed / in a compound / reacted with lithium

nitride

1

plus one of:

• can explode / cause a fire

• is free

• is under pressure

• can leak

• releases quickly

1

(d) (i) loss of an electron or loses electrons

do not accept any ref. to oxygen

1

(ii) full outer shell of 8 electrons on circle

need not be paired

can be ×, dot or e

do not accept if extra electrons added to inner shell

1

[10]

Q18.

(a) (i) hydroxide

1

(ii) blue

1

(b) (i) pipette

1

(ii) burette

1

(iii) changes colour

1

(c) repeat

allow check results with another group or student

1

[6]

Q19.

(a) gives out (heat)

1

(b) D

1

(c) L

1

(d) magnesium chloride

1

[4]

Q20.

(a) (i) ionic

1

(ii) elements

1

(b) (i) chlorine (gas)

allow Cl2 / Cl / Cl2

allow chloride

1

(ii) hydrogen (gas)

allow H / H2 / H2

1

(iii) sodium hydroxide (solution)

allow NaOH

allow sodium solution

1

[5]

Q21.

(a) sensible line of best fit which goes through or close to all the points except

the anomalous point

allow wobbly / short double lines

± ½ square

1

(b) loss of gas / loss of CO2

idea of gas produced / formed

1

(c) 7

1

(d) (i) steeper line from around the same starting point

and left of the points

allow crosses if they are fully correct for 1 mark

1

levelling off at 99

accept short level line at 99

± ½ square

1

(ii) any three from:

• particles / molecules / atoms/ ions have more energy

allow given / gain / get energy

• move faster

ignore move about more

ignore vibrate more / faster

• collide more often

or more chance of collisions

or bump into each other more

ignore collide quicker / faster

• collide with more force / energy

or more particles have the activation energy

or more collisions result in reaction

or more collisions are successful

3

Q22.

(a) electric current / electricity

1

plus one from:

• is passed through ionic compound / substance / electrolyte

• passed through molten/aqueous compound / substance

must be linked to electricity

allow liquid compound / substance

do not allow solution / liquid alone

• causing decomposition

accept split up / breakdown / breaking up owtte

ignore separated

accept elements are formed

ignore new substances form

1

(b) hydrogen

accept H2

do not accept H / H2

1

(c) one electron from each atom

accept each carbon is bonded to three other carbon atoms leaving one (unbonded) electron owtte

1

is delocalised / free (to move)

must be linked to electrons

answers of delocalised / free electrons only, gains 1 mark

accept each carbon is bonded to three other carbon atoms leaving delocalised / free electrons = 2 marks

maximum 1 mark if graphite described as a metal / giant ionic lattice

1

[5]

Q23.

(a) 2Mg + O2 → 2MgO

accept correct multiples / fractions

1

(b)

electrons do not need to be paired

accept dots / circles / e instead of crosses

do not allow 2.6 without diagram

1

(c)

electrons do not need to be paired

allow without bracket s/ must have the charge

accept dots / circles / e instead of crosses

ignore extra empty outer shells

ignore nucleus

do not allow [2.8]2+ without diagram

1

(d) oppositely charged (ions / atoms)

allow positive and negative(ions / atoms)

1

(they) attract

must be in correct context

accept held by electrostatic forces

ignore ionic bonding

maximum 1 if they refer to intermolecular forces / attractions / covalent bonds

1

(e) magnesium chloride

accept MgCl2 (if correctly written)

1

[6]

Q24.

(a) (i) burette

1

(ii) conical flask

accept conical / flask

1

(b) (i) an indicator

1

(ii) changed colour

1

(iii) titration

1

(c) 3

correct answer = 2 marks

(1 × 3) or (1 × 750/250) = 1 mark

1

(d) (i) hydrogen

2

(ii) is partially ionised

1

[9]

Q25.

(a) (an alloy) that can return to its original shape (after being deformed / bent / twisted)

accept (on heating / cooling) it returns to its shape

1

(b) any two from:

• brass / it is a mixture

accept brass / it is not pure

• zinc changes structure / disrupts patterns or layers

• copper metal atoms / layers able to slide over each other

accept zinc prevents atoms / layers sliding over each other

2

(c) (i) oxygen / O2 / O

1

(ii) lead remains (in furnace) because of its high boiling point

1

zinc boils / evaporates (out of furnace) because of its low boiling point 1 if neither mark awarded then allow 1 mark for different boiling points

ignore references to melting points

1

[6]

Q26.

(a) any one from:

• light(er) / less dense

ignore stronger

• resistant to acids / alkalis / chemical

accept resistant to corrosion

1

(b) any two from:

it must be clear

list principle applies

allow reverse argument

ignore reference to temperature

• magnesium is more reactive than titanium

magnesium is above titanium in the reactivity series

• titanium is more reactive than carbon

• magnesium is more reactive than carbon

• magnesium is most reactive

• carbon is least reactive

2

(c) any three from:

it = titanium

ignore references to cost / easier / usefulness alone or references to incorrect processes

• takes a long time to process

• low abundance (of ore)

• small amount produced

• batch process used or blast furnace is continuous

• more stages used to manufacture titanium

allow ≥ 3 / many / several

• more energy used (per tonne of titanium)

allow high energy requirement

ignore references to temperature

• magnesium / chlorine is expensive

• labour intensive

3

[6]

Q27.

(a) (i) (phosphoric) acid

allow phosphoric acid

1

(ii) hydrogen

1

(b) (i) faster / quicker / speeds it up (owtte)

allow answers based on activation energy

ignore helps it to react

1

(ii) most of the starting materials end up as useful products

1

(iii) H2O

allow HOH or OH2

1

[5]

Q28.

(a) (propanone) has a low(er) boiling point

or water has a high(er) boiling point or water evaporates slow(er)

or (propanone) evaporates fast(er) owtte

allow propane / solution / it

allow evaporates at lower temperature or boils quicker

ignore density / reactivity / melting point

1

(b) (i) 0.29

ignore + or –

ignore units

1

(ii) any two sensible suggestions eg:

• weighing error

accept human error or inaccurate measurements

• (copper) lost during washing owtte

allow different washing of electrodes

• (copper) lost during electrolysis / reaction owtte

• electrodes not completely dry

• impurities in the electrode

• copper falling off when removing electrode / copper from cell

ignore timing errors

ignore ‘fair test’

ignore sludge

ignore gases produced

2

(c) any four from:

• impure copper is anode / positive (electrode)

• pure copper is cathode / negative (electrode)

• copper sulfate solution or any soluble copper salt in solution

• copper loses electrons or copper is oxidised(*)

• copper forms positive ions / particles(*)

(*)as alternative to these two points Cu → Cu2+ + 2e– = 2 marks

• copper gains electrons or copper reduced at negative electrode

or Cu2+ + 2e–→Cu at negative electrode

• copper attracts to / collects at negative electrode

• sludge / impurities collect at the bottom owtte

allow sludge left behind or sludge left in solution or impurities separated from copper

• impurities not attracted to electrode

ignore get rid of impurities

4

Q29.

(a) (i) sulfuric

accept H2SO4

accept sulphuric

allow phonetic spellings

1

(ii) CuO + H2SO4 → CuSO4 + H2O

1 mark for reactants

1 mark for products

ignore state symbols

max 1 mark for incorrect balancing

2

(b) any two from:

• particles gain energy or particles have more energy

allow have more activation energy

• particles move faster

allow they collide faster / quicker

ignore move / vibrate more

• collide more often

allow more collisions

• collide more energetically

• more of the collisions are successful

or more particles have the activation energy

NB more successful collisions alone = 1 mark

if particles are identified as electrons = max 1 mark

2

[5]

Q30.

(a) (i) contain enough metal to make it economical / worth while to extract

1

(ii) reduction

accept displacement

accept redox

1

(iii) Fe + CO2

do not accept Fe2 / Fe4

1

correct balancing

accept multiples and halves

2Fe2O3 + 3C → 4Fe + 3CO2

allow Fe2 / Fe4 as ecf

1

(b) Pure Iron

(in pure metal all the atoms are the same size and) able to slip / slide over each

other – (property soft)

OWTTE

ignore references to molecules / particles

if they say ‘move’ both times, allow one mark but ‘crack’ or ‘split’ is wrong..

1

Cast iron

(in cast iron) different sized atoms / larger atoms or structure is distorted / disrupted

OWTTE

1

so it is difficult for layers of atoms to slip / slide over each other

OWTTE

1

(c) any three from:

• conserves / saves resources / metal ores

• saves energy resources (used for extraction / processing)

accept cheaper / saves money

• decreases waste materials

• decreases a named pollution

do not accept acid rain

3

[10]

Q31.

(a) (i) any one from:

• iron ore is a limited resource / non-renewable

• iron is in high demand

• provide jobs

• economic advantage

1

(ii) any two from:

• would damage (wildlife) habitats / countryside / greenfield sites

• extra traffic

• visual (pollution) / eyesore

• noise (pollution) / sound (pollution)

• dust (pollution)

• river (pollution)

• carbon dioxide (from traffic) / adds to greenhouse effect / global

warming

• damage roads / buildings by vibrations / shockwaves

2

(b) (i) carbon monoxide / carbon

accept formulae CO / C

1

(ii) atoms

accept (particles) are all the same (size) / type for one mark

1

are all the same (size) / type

1

(iii) any two from:

• impurities / carbon / different (sized) atoms or elements or metals

• changes the structure / disrupts the pattern or layers

• prevents layers sliding over each other

• it is an alloy

2

Q32.

(a) (i) Cu2S + 2O2 2CuO + SO2

accept fractions and multiple

1

(ii) any two from:

• sulfur dioxide

accept sulphur dioxide / sulphur oxide / SO2

• causes acid rain

ignore other comments eg global warming / ozone / global dimming / greenhouse effect

• consequence of acid rain eg kills fish / plants

2

(b) any two from:

• heat (copper oxide with carbon)

• oxygen is removed by carbon

accept copper (oxide) loses oxygen

or

carbon gains oxygen

accept carbon oxide

or

carbon monoxide / carbon dioxide is produced

or

carbon displaces copper

accept a correct word or balanced

symbol equation

• because carbon is more reactive than copper

allow a correct comparison of reactivity

2

(c) (i) electrolysis

accept electroplating

1

(ii) (electrical) wiring / appliances / coins / pipes / cladding for

buildings / jewellery / making alloys

1

or

named alloys

(d) any three explanations from:

for recycling

• less acid rain (pollution)

• copper reserves last longer / conserved

or

do not run out

• energy for extraction (saved)

or

less energy required

• less mining / quarrying

• less waste (copper) / electrical appliances dumped

or

less landfill

against recycling

• collection problems

• transport problems

• difficult to separate copper from appliances

• energy used to melt the collected copper

ignore electrolysis / pollution

ignore ideas about less machinery / plant

ignore idea of cost

3

[10]

Q33.

(i) potassium hydroxide

accept correct formulae

1

water

1

(ii) fertiliser

1

(iii) H+

accept hydrogen but not H

1

[4]

Q34.

(a) (i) 5(%)

1

(ii) 0.35

for 1 mark

2

(b) (i) reduction

accept (it’s) reduced

do not accept redox / deoxidation

1

(ii) heat with / reduce / react with or (chemical) reaction

1

with a metal / element / substance higher in reactivity

ignore displace

accept higher named elements or symbol

accept carbon monoxide / coal / coke

correct word equation for 2 marks

correct formulas for 1 mark

correct balanced symbol equation for 2 marks

1

or

electrolysis:

molten (1)

electrolysis (1)

[6]

Q35.

(a) H+(aq) + OH– (aq) → H2O(l) or

H3O+(aq) + OH–(aq) → H2O(l)

mark for correct equation

mark for state symbols

any other symbols = 0 marks

accept correct spectator ions e.g.

Na+(aq) + OH– (aq) + H+(aq) + Cl– (aq) → Na+(aq) + Cl– (aq)

+ H2O(l)

2

(b) (i) nitric acid and ammonia (solution)

HNO3 NH3 / NH4OH

mark for both

accept ammonium hydroxide /

NH4OH instead of ammonia

do not accept ammonia hydroxide

do not accept hydrogen nitrate solution

accept correct formulae

1

(ii) provides oxygen or oxidising (agent) or oxidant

do not accept it contains oxygen alone

or rich in oxygen

1

[4]

Q36.

nitric acid

1

potassium hydroxide

1

water

1

[3]

Q37.

(a) hydrogen

accept H2

do not accept H

1

(b) litmus paper / Universal Indicator paper / pH paper

allow any suitable named indicator

1

bleached / turns white or loses its colour

do not accept bleached cloth / leaves etc.

allow second mark unless incorrect indicator given

allow starch iodide paper (1)

goes black / blue black (1)

allow potassium iodide solution (1) goes brown / orange / black precipitate (1)

1

(c) because they have a negative charge or opposite charges attract

accept (because) it is Cl–

accept chlorine, Cl or chlorine ions has a negative charge

do not accept Cl– on its own

do not accept Cl2 o.e. has negative charge

1

(d) kill bacteria / germs, etc. or sterilise / disinfect

accept destroys bacteria etc.

ignore clean / purify water (owtte)

do not accept just gets rid of bacteria

1

(e) hydroxide (ion)

accept OH–

1

[6]

Q38.

(a) 100

ignore units

40 + 12 + (3 × 16) for 1 mark

1

(b) 40

(ecf from part (a) can get 2 marks)

for 1 mark

1

(c) 0.5

(ecf from part (b) can get 2 marks)

or other correct working for 1 mark

2

(d) gas produced or carbon dioxide / CO2 produced

1

[7]

Q39.

(a) react with oxygen / oxidise / burn in oxygen / burning / combustion or

tungsten to tungsten oxide or makes an oxide

key idea is oxidation

ignore breaking ignore fire / flames / exothermic

ignore react with air

1

(b) it is (very) unreactive / not reactive / inert / does not react with tungsten

or it is a noble gas or it is in group 0 or 8 or 18

do not accept unreactive / inert metal or argon is not very reactive

1

full outer shell (of electrons) / 8 electrons in outer shell

1

does not need to gain / lose / swap / transfer / share electrons or does not need to

form bonds

does not bond ionically / covalently

1

[4]

Q40.

(a) Mr (SiO2) = 60

if Mr incorrect ecf for max 2

1

60 g SiO2 → 28 g Si

correct answer for 3 marks

1

2.14 g SiO2 → 1 g Si

allow 2, 2.1, 2.14 (or anything rounding to 2.14), 2.16 or 2.2

a unit is not required but an incorrect unit loses the third mark

OR Mr (SiO2) = 60 (1)

moles if silicon needed = = 0.0357

mass of SiO2 needed = 0.0357 × 60 (1)

= 2.14 g (1)

allow 2, 2.1, 2.14 (or anything rounding to 2.14), 2.16 or 2.2

OR Mr (SiO2) = 60 (1)

mass SiO2 = 1 × (1)

= 2.14 g (1)

allow 2, 2.1, 2.4 (or anything rounding to 2.14), 2.16 or 2.2

3

(b) (i) MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l)

penalise incorrect symbols correctly balanced equation for 1 mark state symbols for 1 mark

allow correct multiples / fractions

2

(ii)

or

ignore inner shell electrons of silicon

allow correct drawings without symbols

must clearly indicate four shared pairs of electrons with one electron from each atom

(iii) Si H

1

= 0.05 = 0.15

1

1 3

for whole number ratio can be implied

1

Si H3

accept H3 Si or any correct formula with 1:3 ratio

if in step 1 they get either of ratios incorrect they lose first 2 marks but can be ecf for 3rd and 4th mark

evidence of mass / Ar 1 mark

proportions of each 1 mark

whole number ratio 1 mark

correct formula 1 mark

1

(iv) C

accept c

1

(c) any four from:

• giant structure / macromolecule / lattice / giant molecule

allow giant molecular / giant atomic structure

• each silicon atom joined to four other atoms

(or diagram)

• covalent bonds

• bonds are strong or large amount of energy needed to break bonds

accept hard to break bonds

• large number of bonds to be broken

mention of giant ionic structure or intermolecular forces or intermolecular bonds max 1 mark

diamond or carbon discussion max 3 marks unless clearly linked to silicon

4

[15]

Q41.

(a)

must be a description of a titration no titration = 0 marks

Quality of written communication

for correct sequencing of 2 of first 3 bullet points i.e. 1 + 2

or 2 + 3 or 1 + 3

1

any three from:

• nitric acid in burette

do not accept biuret

can be inferred from 3rd point

• add nitric acid until indicator changes (colour)

can be named acid-base indicator

colour change does not have to be correct

• note (burette) volume used or final reading

• accuracy: e.g. repeat

accept white tile or dropwise near end or white background or swirling the flask or read meniscus at eye level

3

(b) e.g. formula method:

25 × MNH3 = 0.25 × 20

1

MNH3 = 0.2

correct answer alone = 2

OR

moles NH3 = moles HNO3

= × 0.25 = 0.005 moles (1)

concentration NH3

= = 0.2 (1)

1

(c) sodium hydroxide or potassium hydroxide or lithium hydroxide or calcium

hydroxide

ignore mention of alkali

1

ammonia produced

accept gas produced turns (damp) (red) litmus blue (not blue litmus) or alkaline gas produced

any suitable named indicator e.g. UI with consequential marking white fumes / smoke with (concentrated) HCl

do not accept white gas wrong test = 0 marks

1

[8]

Q42.

(a) (i) water

accept H2O

accept correct ringed answer in box

1

(ii) neutralisation

accept underlining or any indication, eg tick

1

(b) sodium hydroxide

1

sulphuric acid

apply list principletotal

1

[4]

Q43.

(a) (very) small percentage / amount (in the Earth’s crust)

any indication that there is a small

amount, eg not much (left)

accept rare (elements) / rarer

accept not commonly found

ignore cannot find easily

ignore hard to extract

1

(b) (i) oxygen / O / O

do not accept O

1

(ii) any one from:

• potassium / K

• sodium / Na

• calcium / Ca

• magnesium / Mg

symbols must be correct

write name and incorrect symbol,

ignore symbol

1

(c) (i) heating (with) or hot air blown into furnace

accept high temperatures or (very) hot

1

carbon / carbon monoxide / coke / coking coal

do not accept coal / charcoal accept balanced equation only

or

carbon reacts with O2 or carbon / coke burning (1)

accept balanced equation only CO / CO2

CO reacts with the ore (1)

for naming the reducing agent

1

(ii) cost of melting ore / electricity

makes aluminium expensive (owtte)

or (large amount of) electricity used

or because you have to use electrolysis

or aluminium is higher in the reactivity series

or aluminium is harder to reduce

or unable to reduce with carbon

or the cost of purifying the bauxite

do not accept harder to extract / produce

more energy is not enough

1

[6]

Q44.

hydrogen ions (from acid) or protons / H+

1

react with hydroxide ions (from alkali) / OH

1

to produce water

H + OH H2O gains all 3 marks

ignore state symbols

molecules of hydrogen ions and molecules of

hydroxide ions produce water = 2 marks

if they fail to get any of the above marks they can

get 1 mark for neutralisation / product neutral

1

[3]

Q45.

(a) (i) to remove or separate copper oxide

accept to remove or separate

unreacted or excess base

accept to remove or separate insoluble solids

1

(ii) heat (the solution)

accept heat the water

accept evaporate the water

rapid cooling/cool to lower temperature

accept boil the water or solution

not increase surface area, put in

draught

not increase the temperature

1

(iii) aqueous

accept in water

accept solution

not soluble in water

1

(b) add water/liquid/solution

1

colour changes to blue

1

[5]

Q46.

(a) (i) must be chemical symbol

Ca

1

C

CaCO3= 2 marks

1

O not O2

1

(ii) carbon dioxide

must be name

1

(b) (i) points all correct 2 marks

one point incorrect 1 mark

two points incorrect 0 marks

2

suitable line -narrow neat single curve

not dot to dot

1

(ii) reaction with X forms less gas

must include X or Y

do not penalise for H2/O2 if (a) (ii) already penalised

do not accept is finished in less time or slower/faster reaction or lower on graph

1

(iii) any two from:

• concentration (of acid) decreases/less reacting particles/molecules

not acid/CaCO3 runs out/is used up

• surface area of calcium carbonate decreases

not strength of acid decreases

• less collisions between reacting particles

not smaller (amount of) CaCO3

2

[10]

Q47.

(a) (i)

calcium carbonate → calcium oxide + carbon dioxide

accept CaO3 → CaO + CO2

1

(ii) (thermal) decomposition

accept endothermic

accept reversible

1

(b) (i) neutralisation

accept exothermic

1

(ii) sulphuric (acid) H2SO4

2

(c) (i) to speed up the reaction

accept to increase the rate of reaction or to increase the number or rate of collisions

do not accept “dissolves” copper oxide faster

1

(ii) all acid reacts

accept there will be no acid left or acid used up

1

acid is neutralised (for 2 marks)

do not accept to form a concentrated or saturated solution

1

(excess) copper oxide collects in filter paper

accept larger particles (of copper oxide) cannot pass through filter paper

1

copper sulphate solution passes through the filter paper

accept dissolved copper sulphate passes through filter paper or smaller particles (of copper sulphate) in solution (liquid) pass through filter paper

accept (black) solid collects in filter paper and filtrate or soluble solid or (blue) solution (liquid) passes through filter paper for 1 mark only

1

[10]

Q48.

(a) 0 – 6

1

(b) more accurate

1

(c) burette

1

(d) sodium hydroxide / potassium hydroxide / ammonia / any other soluble

Group I or II hydroxide

1

(e) (i) named indicator / litmus / U.I. / methyl orange / methyl red / phenolphthalein

1

(iii) colour at end point

1

[6]

Q49.

(a) (i) bulb lights up

1

bubbles / fizz / gas or chlorine given off

1

(ii) in solid, ions

1

are not free to move / (charged) particles cannot move or converse

atoms / electrons cannot move worth 0 marks

1

(b) (i) breakdown / decomposition / splitting up

not separation

1

by using electricity

1

(ii) gas A = chlorine / oxygen

1

deposit B = copper

1

(c) any one from:

• manufacturer of chlorine / sodium hydroxide / hydrogen / sodium

• electroplating of steel / reference to plating

not galvanising

• extraction of aluminium / metal reactivity series specified

• purification of copper

not making copper

1

[9]

Q50.

(i) electrolysis

1

(ii) oxidation

1

(iii) hydroxide ions or OH–

accept sodium hydroxide or hydroxide or OH for one mark only

2

(iv) H+ + e–

1

H2

ignore any state symbols

1

2H+ + 2e– → H2

accept H+ + e-→ H for one mark only

1

[7]

Q51.

(a) any four from:

• sulphuric acid measure by pipette

or diagram

• potassium hydroxide in burette

or diagram

• if solutions reversed, award

• note initial reading

• use of indicator

• note final reading or amount used

4

(b)

1

= 0.068

1

(c) ½ or 0.5 moles H2SO4 react with 1 mole KOH

1

moles H2SO4 in 25.0 cm3 = 0.068 × 0.5

1

moles H2SO4 in 1 dm3 = = 1.36 mol/dm3

1

[9]

Q52.

(i) Mg + (H2SO4) →

1

MgSO4 +

1

H2

deduct 1 mark if not balanced only if all three correct

accept alternative metal of similar reactivity for example Zn or Fe candidate would not then be awarded first mark for Mg

then error carried forward

deduct 1 mark if not balanced only if all three correct

1

(ii) to remove the (excess) magnesium

accept separate

accept insoluble substances or solids or residue

do not accept unreactive substances or impurities or remove magnesium from sulphuric acid

1

(iii) to evaporate (some of the water or solution)

1

to form crystals or crystallise

accept to form a saturated solution

or concentrated solution

do not accept to leave MgSO4

1

[6]

Q53.

(a) breakdown / decomposition / splits into elements /

not ions

separates into elements / produce a chemical reaction

1

using electricity

1

(b) lead bromide melted / free ions

not electrolyte

1

(c) (+) bromine

element must be appropriate to electrode

1

(–) lead

element must be appropriate to electrode

1

(d) fume cupboard / protective clothing

allow safety glasses

not safety mat

1

[6]

Q54.

(a) (i) test: limewater

accept calcium hydroxide solution

1

result: ‘goes’ cloudy

accept white or milky

do not accept misty or chalky test must be correct before result mark can be considered

1

(ii) 2 NaHCO3 + H2SO4 →

Na2SO4 + (2) H2O + (2) CO2

1

correctly balanced

1

(b) (i) H+ + OH–

1

→ H2O

deduct one mark if incorrectly balanced

accept H3O+ instead of H+ then 2H2O needed for balance

1

(ii) pH increases

accept numerical indication

1

(c) addition of sulphuric acid

1

correct use of an indicator

accept idea of forming a neutral solution

1

crystallisation (of neutral solution)

accept description using evaporation

1

[10]

Q55.

(a) mixture

not compound

1

of a metal with other element(s) / metals

not of elements

not of a metal with other substances

1

(b) steel

allow stainless steel

1

(c) stronger / increased strength / harder / less malleable / less brittle

not corrosion / rusting

1

(d) copper and zinc

1

[5]

Q56.

(a) substance brokendown / separates / splits into elements

by electric current / electricity

ions free to move e.g. when molten / in solution

allow 1 mark for “a substance that conducts electricity”

max 2

(b) (i) copper / Cu

1

(ii) oxygen /O2

allow CO2

1

(c) tube over electrode

full of CuSO4(aq) / water

allow sulphuric acid / sensible electrolyte

not any other liquid / using a syringe

2

(d) Cu2+ ions removed / less Cu2+

not copper sulphate removed

allow 1 mark for “copper removed / less copper”

2

[8]

Q57.

(a) (i) H2SO4 or red (acidic) pH < 7

accept names of compounds

accept correct use of acidic

1

NaOH or purple (alkaline) pH > 7

alkaline and neutral without any mention of pH for 1 mark only

1

NaCl or green (neutral) pH 7

ignore high or low pH

1

(ii) hydrogen (ion)

accept proton

accept hydroxonium ion

1

H+

accept H3O+ for hydroxonium ion

1

(b) (i) neutralisation

1

(ii) NaOH + HCl

ignore state symbols

1

NaCl + H2O

ignore state symbols

maximum of 1 mark if incorrectly balanced

1

(c) (i) sodium – 2 . 8 . 1

accept 2.8.1 written

1

chlorine – 2 . 8 . 7

accept 2.8.7 written

1

(ii) ion(s)

1

(iii) attraction between oppositely charged particles (ions)

accept attraction between + and – particles (ions)

accept electrostatic attraction

1

(d) chloride ions lose electrons to form chlorine

Cl– – e– → Cl

1

hydrogen ions gain electrons to form hydrogen

H+ + e– → H

1

sodium hydroxide remains in solution

Na + and OH– remain in solution to form sodium hydroxide

1

[15]