Chemical Changes part 2 Mark schemes

Q1.

(a) Will kelp last longer than coal as an energy source?

1

(b) any two from:

• cannot be determined by experiment

allow can’t predict how long kelp / coal will last

allow more testing needed

• based on opinion

• ethical or environmental or economic reason

allow could damage ecosystem allow reference to cost

2

(c) (i) 7

1

(ii) sodium (atom) loses (electron) and iodine (atom) gains (an electron)

reference to incorrect bonding or incorrectly named particle

= max 2

any or all marks can be obtained from a labelled diagram

ignore inner shell electrons if shown

1

1 electron

1

(electrostatic) attraction or forms ionic bond(s)

1

(iii) ions can move (in the solution)

1

(iv) 2 I – I 2 + 2 e –

1

(v) hydrogen is formed

1

because sodium is more reactive (than hydrogen)

1

[11]

Q2.

(a) (i) copper / Cu

1

(ii) 50 (p)

1

(iii) 25

1

(iv) tin

1

(b) any one form:

• high cost of copper

allow metal is expensive

• less copper available or (copper ores exhausted / only low-grade ores available)

allow copper is non-renewable

• high demand for copper

• high percentage (%) of copper in the coin

• inflation (of cost)

1

[5]

Q3.

(a) fertilisers

1

(b) air

1

(c) speeds up the reaction

accept lowers the activation energy

ignore makes the reaction work

1

(d) reversible reaction

1

(e) (i) 10

1

(ii) water

accept H2O / hydrogen oxide

1

[6]

Q4.

(a) cannot move

1

(b) (i) a positive charge

1

(ii) atoms

1

[3]

Q5.

(a) he made urea / organic compound / he made another organic compound

ignore he made it unless qualified eg accept he made it from non-living material / not made from animals / plants

1

(b) any one from:

sensible ideas eg

• famous scientists / eminent scientists / high status scientists accepted

the life-force theory

• sensible references to lack of status of Wöhler

• was not in line with accepted ideas of time / religious beliefs etc

eg it was a new idea

• other sensible answers eg fake / anomalous results

or lack of evidence / proof

accept only made 1 compound

ignore no evidence

or not reliable / reproduced

or not repeated

1

(c) sensible ideas such as:

accept ‘other scientists repeated his experiment / made other organic compounds’

Wöhler made another organic compound or more evidence or repeated it

allow more proof

ignore he proved it

1

(d) (i) nitric (acid)

spelling must be correct

accept HNO3 correctly written

ignore hydrogen nitrate

1

(ii) evaporate

allow heat / boil / cool

or

allow to crystallise

do not allow freeze

ignore filtration unless as an alternative

ignore distillation

ignore solidify

1

[5]

Q6.

(a) (i) H+

1

(ii) OH–

1

(b) with ethanoic acid:

‘it’ refers to ethanoic acid

UI goes Orange/yellow

1

but HCl goes red/pink

1

or

ethanoic acid has pH 4 or above but less than 7 (1)

but HCl has a pH3 / or lower (1)

(c) completely

1

(d) (i) conical flask

1

(ii) titration

1

(iii) repeat

or

take average

allow compare with another student's results

1

[8]

Q7.

(a) (i) aluminium oxide

ignore (III) after aluminium

1

(ii) (because it provides) heat / energy (to overcome activation energy)

1

(b) (i) contains only one sort of atom

1

(ii) the atoms (in cast iron) are different sizes

any mention of molecules, maximum 1 mark

accept layers are distorted or structure is disrupted

1

which prevents the layers / rows sliding

accept an answer in terms of pure iron being softer than cast iron for both marks

1

(c) (i) because aluminium is more reactive than carbon

‘it’ = aluminium must be a comparison between the elements

or

because aluminium is above carbon in the reactivity series

do not accept any comparison of the reactivity of aluminium and iron

1

(ii) reduces / lowers the temperature for the process or lowers the operating temperature or allows ions to move

ignore any temperature values

allow reduces the (effective) melting point (of Al2O3 )

1

(iii) 3

accept multiples

1

(iv) electrons are gained (by Al3+)

ignore any numbers

ignore any reference to oxygen

1

(v) electrodes are made of carbon

allow graphite / coke

1

oxygen is produced (at the positive electrode / anode)

accept 2O2− → O2 + 4e−

1

so the electrodes react with the oxygen / are oxidised

1

producing carbon dioxide (gas)

accept C + O2 → CO2 for marking points 3 and 4.

1

[13]

Q8.

(a) (i) any two from:

• bubbles / effervescence / fizzing

ignore hydrogen / gas produced

• lithium disappears / gets smaller

allow dissolves

do not allow melts / burns

• lithium moves on the surface of the water

ignore floats

• (universal indicator) turns blue / purple

2

(ii) 2

left-hand side correct

1

2

right-hand side correct

allow multiples for full credit

1

(iii) light / burn, which will give a (squeaky) pop / explosion

1

(iv) all have 1 electron in their outer shell / energy level

allow have the same number of electrons in their outer shell / energy level

1

(b) They react with oxygen

1

They have low melting points

1

(c) (i) electronic structure [2,8,8] is drawn

incomplete inner shells scores a maximum of 1 mark

1

charge is +

allow [2,8,8]+ for 1 mark

1

(ii) because (in potassium) the outer shell electron is further away from the nucleus or because potassium atoms are larger than sodium atoms

it should be clear that the candidate is referring to the outer shell electron: if this is not clear a maximum of 2 marks can be awarded

1

therefore the outer shell electron is less strongly attracted to the nucleus or is more shielded from the attraction of the nucleus and so the outer shell electron in potassium is more easily lost

1

3 marks can be scored for answering the question in terms of sodium

1

[13]

Q9.

(a) (s) (aq) (aq) (g)

must be in this order

2 marks if all four correct

1 mark if 2 or 3 correct

2

(b) (i) 55

ignore units

1

(ii) 54

allow ecf from (b)(i)

1

(iii) 0.92

correct answer with or without working gains 2 marks

ecf from volume in (b)(i)

accept 2 d.p. up to calculator value

if answer incorrect, allow rate = (b)(i) / 60 for 1 mark

2

(c) (i) circle round point at (48,22)

1

(ii) problem (1) and explanation (1)

explanation must give lower volume of gas or slower reaction

ignore human error unless qualified

problem with bung

e.g. bung not placed in firmly / quickly enough

so gas lost

or

problem with reagent

e.g. acid was diluted or acid not replaced

so reaction slower

or

problem with temperature

e.g. temperature was lower than recorded temperature

so reaction slower

or

problem with measurement

e.g. length of magnesium less than 8 cm or timed for less than a minute

so less gas produced

2

(d) repeat the experiment (several times)

1

because anomalous results could be excluded

1

and then the mean can be determined / calculated

accept suggestion of alteration to method, which is explained as to why it would reduce the error, for 3 marks (e.g. place the magnesium in a container within the flask (1) so it can be tipped into the acid once the bung is in place (1). This will prevent anomalous results or gas loss (1))

ignore idea of more accurate gas syringe

ignore shorter time intervals

1

(e) (i) use clean magnesium or use magnesium without oxide coating

1

compare results

1

(ii) either

measure the temperature of the acid before (adding magnesium)

1

and after adding magnesium

or

place the conical flask in a water bath (at 40 °C) (1)

compare results (1)

1

[16]

Q10.

(a) (i) red

ignore pink

1

(ii) add silver nitrate (solution)

1

white precipitate

dependent on addition of silver nitrate

ignore addition of another acid

if hydrochloric acid added max 1 mark

1

(b) suitable named alkali / sodium hydroxide solution in burette

1

add alkali solution until (indicator) becomes pink / red

1

if acid to acid titration described, first two marking points not available

any two from:

• wash / rinse equipment

• add dropwise or slowly (near end point)

• swirl / mix

• read (meniscus) at eye level

• white background

• read start and final burette levels / calculate the volume needed

• repeat

2

(c) does not ionise / dissociate completely

allow for acids of the same concentration, weak acids have a higher pH or fewer hydrogen ions

1

(d) (i) ring round COOH

1

(ii)

if not fully correct, allow 1 mark for correct ester group − minimum

2

[11]

Q11.

(a)

one mark for each substance linked correctly to its description

do not accept more than one line from each substance

3

(b) 0 / zero / none / no charge

1

electron

1

(c) (i) nucleus

1

(ii) atomic number

1

(iii) mass number

1

[8]

Q12.

(a) (i) ethene

allow C2H4

1

(ii)

accept line drawn from word ‘Monomer’ or from the monomer box to the correct ‘Polymer’

allow the correct ‘Polymer’ indicated by a tick, circled etc.

1

(b) (i) nickel

accept Ni

1

(ii) 75(%)

1

(iii) (stainless steel) is hard /strong / durable

it = stainless steel

accept (pure) iron is soft

1

(stainless steel) resistant to corrosion or unreactive

accept (pure) iron rusts / corrodes / reacts

do not allow corrosive

1

(c) Advantage : Conserves resources of crude oil and ores

do not allow more than one tick in the advantage column

1

Disadvantage : High cost of separating materials

do not allow more than one tick in the disadvantage column

1

[8]

Q13.

(a) any two from:

• copper / ores are running out / harder to find

• there are no / very small amounts of high-grade copper ores left

• copper metal is in demand

• copper is expensive

• now economical to extract copper from low-grade ores

it = copper

allow new methods of extraction e.g. bioleaching and phytomining

allow high-grade ores are running out for 2 marks

2

(b) (i) large amounts / 98% of rock to dispose of as waste

accept contains toxic (metal) compounds / bioleacher

or

waste rock takes up a lot of space

1

(ii) (copper sulfide reacts with oxygen to) produce sulfur dioxide / SO2

allow (sulfur reacts with oxygen to) produce sulfur dioxide / SO2

1

that causes acid rain

allow description of effects of acid rain or sulfur dioxide

if no other mark awarded allow CO2 produced which causes global warming or CO2 produced by burning fuel or heating the furnace for 1 mark

1

(iii) any one from:

• large amounts of fuels / energy used (for the furnace and electrolysis)

allow large amounts of electricity needed

ignore high temperature / electrolysis unqualified

• (the extraction has) many steps / stages / processes

allow (extraction) is a long process / takes a lot of time

• large amounts of ore / material have to be mined

allow ores contain a low percentage of copper

1

(iv) (copper ions move towards) the negative electrode / cathode

1

because copper ions / Cu2+ are positively charged or are oppositely charged or copper ions need to gain electrons

allow because metal ions are positive or opposites attract

1

(v) (growing) plants

1

[9]

Q14.

(a) (i) 2.8.3

any sensible symbol can be used to represent an electron

1

(ii) proton(s) and neutron(s)

both needed for the mark

1

(iii) number of protons is equal to number of electrons

allow positive and negative charges cancel out

allow same amount of protons and electrons

1

(b) (i) 2 Al + Fe2 O3 → 2 Fe + Al2 O3

equation must be balanced

1

(ii) aluminium is more reactive (than iron)

it = aluminium

accept converse

accept aluminium displaces iron

accept aluminium is higher in the reactivity series (than iron)

1

[5]

Q15.

(a) any one advantage from:

• conserves resources (of crude oil / metal ores)

ignore can be made into other items

allow the materials (in the pen) are non-renewable

allow less expensive than producing from the raw material

• reduces use of landfill

ignore less waste

• less use of fuels/energy

• less carbon dioxide produced

ignore global warming unqualified

1

any one disadvantage from:

• made of different polymers / alloys / materials

• difficulty / cost of separating the different materials

allow not all the materials can be recycled

1

(b) hard / strong / durable

1

resistant to corrosion or unreactive

allow do not rust

do not allow corrosive

1

(c) (i) vapours (of decane)

ignore pressure / hot / heat

allow high temperature (≥150 °C)

1

passed over a catalyst or porous pot or aluminium oxide

allow catalyst even if incorrectly named

1

or

mixed with steam (1)

at a (very) high temperature (1)

if temperature quoted, must be ≥ 500 °C

(ii) many monomers or many ethene molecules

1

join / bond

allow addition polymerisation for second mark

1

OR

monomers / ethene molecules (1)

form chains or very large molecules (1)

if no other mark awarded allow double bond breaks / opens up or double bond forms a single bond for 1 mark

(d)

allow bonds that do not extend through brackets

7 single bonds are used and are in the correct places with no additional atoms (1)

the brackets and the n are in the correct place (1)

2

[10]

Q16.

(a) (i) was well qualified

1

(ii) check the results of the experiment

1

(b) (i) cannot move

1

(ii) melt it / make it a liquid

allow heat it

allow dissolve (in water) / make a solution

1

(iii) they are positive

allow opposites attract or opposite charges

1

(iv) atoms

1

[6]

Q17.

(a) any two from:

• effervescence / bubbles / fizzing

allow gas / hydrogen is given off

allow volume of gas

allow magnesium floats

• magnesium disappears / dissolves

allow change in mass of magnesium

• heat given off / exothermic

allow temperature change

do not accept temperature decreases

• change in pH

do not accept pH decreases

2

(b) Marks awarded for this answer will be determined by the Quality of Written Communication (QWC) as well as the standard of the scientific response. Examiners should also refer to the information in the Marking guidance.

0 marks

No relevant content.

Level 1 (1-2 marks)

A simple plan without reference to changing any variable but should include an attempt at measuring rate or an attempt at fair testing

Level 2 (3-4 marks)

A plan including change of concentration / ‘volume’ of acid and should include an attempt at measuring rate and / or an attempt at fair testing

Level 3 (5-6 marks)

A workable plan including change of concentration and measurement of rate and fair testing

Examples of chemistry points made in the response could include:

Plan:

• add magnesium to acid

• time reaction / ‘count bubbles’ / measure volume of gas

• change concentration / ‘volume’ of acid

Control Variables:

• amount / mass / length / same ‘size’ of magnesium

• volume / amount of acid

6

[8]

Q18.

(a) (i) current / charge couldn’t flow

allow could not conduct (electricity)

1

because the ions / particles couldn’t move

do not accept electrons/ molecules / atoms

or

(salt) needs to be molten / (1) dissolved (to conduct electricity)

so that the ions / particles can move (1)

do not accept electrons / molecules / atoms

1

(ii) he had status

accept he had authority or experience

or

he had evidence / proof

accept the experiment could be repeated

1

(b) hydrogen / H2

do not allow hydrogen ions

1

the ions are positive

accept because opposite (charges) attract

1

potassium is more reactive (than hydrogen)

accept potassium ions are less easily discharged (than hydrogen)

or potassium ions are less easily reduced (than hydrogen)

1

(c) (i) gain electron(s)

accept fully balanced correct equation for 2 marks

1

one electron

if no other marks awarded allow (potassium ions) reduced for 1 mark

1

(ii) 2 Cl– → Cl2 + 2e–

must be completely correct, including charge on electron

accept correct multiples

1

(iii) 2, 8, 8

accept any combination of dots, crosses, “e” or any other relevant symbol

ignore any charges if given

1

[10]

Q19.

(a) (i) hydrogen

accept H2

allow H

1

(ii) hydroxide

accept OH–

allow OH

do not accept lithium hydroxide

1

(b) any two from:

‘it’ = potassium

potassium:

accept converse for lithium

• reacts / dissolves faster

allow reacts more vigorously / quickly / violently / explodes

ignore reacts more

• bubbles / fizzes faster

allow fizzes more

allow more gas

• moves faster (on the surface)

allow moves more

• melts

allow forms a sphere

• produces (lilac / purple) flame

allow catches fire / ignites

do not accept other colours

2

[4]

Q20.

(a) reduction

1

(b) carbon is less reactive than aluminium

1

(c) aluminium (ions) / they are positively charged

they = aluminium ions

ignore particle names

accept aluminium (ions) / they are cations

allow aluminium (ions they have an opposite charge

1

so they are attracted or they move towards the negative electrode

OR

aluminium (ions) / they need to gain electrons (1)

which come from the negative electrode (1)

if no other marks awarded allow ‘opposites attract’ for 1 mark

1

(d) aluminium has a low density

1

aluminium is resistant to corrosion

1

(e) advantage less carbon dioxide is produced

1

disadvantage used aluminium cans have to be collected and transported

1

[8]

Q21.

(a) (i) reduction

accept redox / smelting

1

(ii) 3 4 3

1

(b) (i) 55

ignore other units

(ii) Water

accept sodium hydroxide

accept correct formulae H2O or NaOH

1

(iii) any one from:

• save energy / fuel for transporting the ore

accept less (cost of) transport allow transported quickly

• (old) quarries nearby for waste/red mud

1

(c) Environmental

any one from:

• less mining / quarrying (of bauxite)

allow loss of habitat / less qualified noise pollution

• less landfill space needed / used

allow less red mud / waste

• less use of fossil fuels / energy

• less carbon dioxide produced

1

Ethical or social

any one from:

• saves resources

allow using resources more than once

• creates (local) employment

if answers reversed and both correct award 1 mark

• more people aware of the need for recycling

allow less qualified noise pollution if not given in environmental

1

[7]

Q22.

(a) limewater or calcium hydroxide solution

1

(reacts with carbon dioxide and) turns cloudy / milky

linked to first point

if no other mark awarded ‘puts out lighted splint’ gains 1 mark

1

(b) (i) any two from:

• same volume / amount of the acids

• concentration of the acids

• temperature

• same surface area / size / mass / amount of calcium carbonate

• same measuring equipment

2

(ii) any three from:

• (after about 4 minutes) the sulfuric acid stops reacting or nitric acid continues to react

accept more CO2 with nitric acid at any time after 4 minutes

• (initially) the reaction with sulfuric acid is faster

• (the reaction stops) because calcium sulfate is a solid

allow sulfuric acid produces a solid

• (the reaction continues) because calcium nitrate is soluble / in solution / aqueous

allow nitric acid produces an (aqueous) solution

• because the calcium sulfate prevents the sulfuric acid reacting with the calcium carbonate

• (the rate is faster) because sulfuric acid contains two hydrogens

3

[7]

Q23.

(a) (iron (steel) is) strong

allow abundant or easy to extract or cheap

ignore other correct properties

1

(b) less dense

allow low mass

1

more abundant

accept copper is ‘running out’

allow copper is more expensive

ignore other correct statements

1

(c) (i) C2H4

1

(ii) double bond

1

(iii) poly(ethene)

1

[6]

Q24.

(a) (i) 10

1

(ii) OH-

1

(b) (i) air

1

(ii) particles move faster

1

particles collide more often

1

(iii) catalyst(s)

1

(c) liquid

1

[7]

Q25.

(a) (i) A

1

(ii) E

1

(b) (i) insoluble

precipitation

2

(ii) filtration

accept decant or centrifuge

1

(iii) hydrochloric acid

1

(c) (i) melt

allow add to / dissolve in water

allow heat until liquid

allow turn it to liquid / make it molten

ignore heat

1

(ii) they are positive

or

opposite charges or opposites attract

do not accept electrodes attracting

do not accept positive electrons

1

(iii) chlorine

accept Cl2

do not accept chloride

1

[9]

Q26.

(a) any one from:

• no method / electrolysis / equipment / technology

allow ‘didn’t know how to’ or ‘no knowledge’

• aluminium is a very reactive metal

• high melting point

allow ‘couldn’t heat it enough’

• potassium had not been discovered

1

(b) because others / scientists / they could not repeat the experiment

ignore he could not repeat the experiment

or

others / they could not obtain the same results

1

(c) reaction is endothermic or

reaction takes in heat / energy

accept activation energy

ignore rate / high temperature

ignore bonds broken

1

(d) (aluminium chloride + potassium) → aluminium + potassium chloride

in either order

accept correct formulae

ignore metal

ignore balancing

1

(e) when tested it had the properties of a metal

accept a test for a metal property eg conductivity / reaction with acid

1

properties were different (from other known metals)

accept properties compared with other metals

1

[6]

Q27.

(a) ignore any attempts to change the charge on chloride ion

2.8.2 (drawn as dots or crosses on the circles)

accept e instead of dots or crosses

1

2.8.8 (drawn as dots or crosses on the circles)

1

(b) (i) filtration

accept decanting or centrifugation

do not accept evaporation

1

(ii) hydrochloric

accept HCl

1

(c) (i) so that ions / particles can move (in electrolyte)

allow so it can conduct electricity / carry charge / carry current

ignore reference to electrons moving in the external circuit

any unqualified reference to electrons moving / carrying charge / carrying current = 0 marks

1

(ii) electrons are lost

ignore numbers

1

(iii) + 2e– on left hand side of equation

must be correct with no other additions

accept correct multiples

1

[7]

Q28.

(a) sodium has a lower density

1

sodium is more reactive

1

(b) hydrogen

1

(c) OH–(aq)

1

[4]

Q29.

(a) it / brown colour has a high(er) boiling point

allow it / brown colour is a solid

1

(b) (i) partially

1

(ii) for ethanoic acid –

accept converse points for hydrochloric acid

fewer bubbles or gas produced at a slower rate

1

more magnesium remains or

magnesium disappears more slowly

accept less temperature rise or less energy released for ethanoic acid

1

(c) (i) pipette

1

conical flask

1

burette

answers must be in the order shown

1

(ii) indicator

1

colour changes

if indicator named then any stated colours must be correct

1

(d) (i) 23.5 is anomalous / rough titration / overshot

1

the mean of the other 3 is 20.0

1

(ii) (no)

it only contained 4.8g of ethanoic acid in 100cm3

1

[12]

Q30.

(a) (i) react

allow neutralise

allow bubbles / fizzes

accept produces gas / CO2F

ignore rises

1

(ii) stop reacting / producing

stops on its own is insufficient allow stop working / bubbling / fizzing

1

the (hydrochloric) acid / (calcium) carbonate is used up

accept because the (calcium) carbonate has neutralised the (hydrochloric) acid

OR

have been used up (1)

the graph line becomes horizontal / levels out (1)

OR

stays the same / no change (1)

ignore reference to graph line

no further reaction (1)

1

(iii) bubble the gas through limewater / calcium hydroxide solution

allow (add) limewater

test must be correct to gain result mark

1

(the solution) goes cloudy

allow milky

1

(b) advantage > Quarrying limestone provides building materials,

employment and new road links

1

disadvantage > Quarrying limestone releases dust, and lorries

release carbon dioxide from burning diesel fuel

1

[7]

Q31.

(a) (i) cryolite

1

(ii) lower the melting point of the aluminium oxide

1

(b) (i) opposite charges or oxide ions are negative

1

attract

1

(ii) carbon

1

(iii) reacts with oxygen or forms carbon dioxide

accept burns

1

(c) Structure mark:

either Al (atoms) in layers / rows

accept Al (atoms) all the same size

allow Al (atoms) in lines

or alloy (atoms) not in layers / rows

accept different sizes of atoms in alloy

allow alloy (atoms) not in lines

1

Sliding mark:

either so (Al layers) can slide

or so (alloy) layers cannot slide

1

[8]

Q32.

(a) Marks awarded for this answer will be determined by the Quality of Written Communication (QWC) as well as the standard of the scientific response.

Examiners should also apply a "best-fit" approach to the marking.

0 marks

No relevant content.

Level 1 (1-2 marks)

There is a simple description of a laboratory procedure for obtaining potassium chloride.

Level 2 (3-4 marks)

There is a clear description of a laboratory procedure for obtaining potassium chloride from potassium hydroxide solution and hydrochloric acid that does not necessarily allow the procedure to be completed successfully by another person. The answer must include the use of an indicator or a method of obtaining crystals.

Level 3 (5-6 marks)

There is a detailed description of a laboratory procedure for obtaining potassium chloride from potassium hydroxide solution and hydrochloric acid that can be followed by another person. The answer must include the use of an indicator and a method of obtaining crystals.

examples of the chemistry/social points made in the response:

• One reagent in beaker (or similar)

• Add (any named) indicator

• Add other reagent

• Swirl or mix

• Add dropwise near end point

• Stop addition at change of indicator colour

• Note volume of reagent added

• Repeat without indicator, adding same volume of reagent or remove indicator using charcoal

• Pour solution into basin / dish

• Heat (using Bunsen burner)

• Leave to crystallise / leave for water to evaporate / boil off water

Accept any answers based on titration

6

(b) nitric (acid)

allow HNO3

ignore incorrect formula

1

(c) (i) because it is a fertiliser / helps plants grow

allow plant food

do not accept pesticide / herbicide / neutralising soil

1

(ii) tick by: ‘Should farmers stop using ammonium nitrate on their land?’

1

any two from:

• cannot be done by experiment

accept difficult to get / not enough evidence

• based on opinion / view

allow must be done by survey

• ethical or economic issue

if top box ticked allow 1 mark for drinking water varies from place to place

2

[11]

Q33.

(a) 52.9(411765) / 53

correct answer with or without working = 2 marks

if answer incorrect allow 2 x 27= 54 or 27/102 x 100 or 26.5 for 1 mark

2

(b) (i) because it lowers the melting point (of the aluminium oxide)

allow lowers the temperature needed

do not accept lowers boiling point

1

so less energy is needed (to melt it)

accept so that the cell / equipment does not melt

1

(ii) 2 O2– on left hand side

accept correct multiples or fractions

1

4e– on right hand side

accept –4e– on left hand side

1

(iii) because the electrode reacts with oxygen or

because the electrode burns

1

to form carbon dioxide or

electrode made from carbon / graphite

1

[8]

Q34.

(a) causes dust pollution

1

increases traffic

1

(b) (i) it is soft

accept the layers of atoms can slide over each other

ignore other properties

1

(ii) contains chromium / nickel

allow contains other metals

1

(c) (i) an element

1

(ii) hard

1

(iii) is resistant to corrosion

1

[7]

Q35.

(a) (i) contains enough metal to make it economical to extract

1

(ii) Fe (+) CO2

formula of both products must be correct

1

(Fe2O3) (+) ....3....(CO)

→

.....2.....(Fe) (+) .....3...(CO2)

balancing correct

allow correct balancing using Fe2

1

(iii) reduction

accept redox

1

(b) (i) oxygen reacts with the carbon to produce carbon dioxide

allow carbon monoxide for carbon dioxide

1

OR

carbon dioxide is produced (1)

which escapes as a gas (1)

1

(ii) to give steels with different / particular properties or for

different / particular uses

ignore to make different alloys

1

(c) copper is very expensive

accept the metal (iron / steel) costs less than copper

ignore energy

1

because copper ores are ‘low grade’ / running out

allow copper is rare

ignore nickel

1

[9]

Q36.

(a) (i) hydrochloric

1

(ii) insoluble

1

filtration

1

(iii) crystallisation

1

(b) any four from:

any reference to incorrect bonding = max 3

• calcium atom reacts with 2 chlorine atoms

• calcium atoms lose electrons

accept calcium ion is formed

• lose two electrons

accept calcium has a 2+ charge / calcium ion has a 2+ charge

allow Ca2+

• chlorine atoms gain electrons

accept chloride ion formed

• gain one electron

accept chlorine / chloride has a negative charge / is a negative ion/ is a negative particle

allow Cl–

if no other marks awarded allow ionic bonding or complete outer shell for 1 mark

4

[8]

Q37.

(a) any one from:

• they are negative / anions

allow Cl–

ignore atoms / chlorine

do not accept chloride ions are negative electrodes

• they are attracted

• they are oppositely charged

1

(b) hydrogen is less reactive than sodium

1

(c) hydroxide (ions) / OH–

ignore OH

do not accept NaOH / sodium hydroxide

1

(d) (i)

allow any combination of dots or crosses

ignore chemical symbols

1

(ii) covalent

allow close spelling errors

apply list principle

1

(iii) hydrogen (ion) / H+

ignore (aq) / H

do not accept hydrochloric acid / HCl

apply list principle

1

[6]

Q38.

(a) (i) hydrochloric (acid) / HCl

allow phonetic spelling

ignore incorrect formula

ignore state symbols

1

(ii) idea of a solid / insoluble substance being formed (from solutions)

accept solid / insoluble product

ignore cloudy

do not accept evaporation

1

(iii) filtration / filter

accept decanting / centrifugation

ignore evaporate if after filtering

1

(iv) idea of making safe (to eat)

allow remove harmful substances / organisms or sterilisation

or

idea of purification

or

idea of neutralisation

1

(v) crystallisation

accept evaporation / heating / boiling

allow cooling

do not allow freezing / solidifying

1

(b) (i) 2e–

accept e– + e–

ignore working out

1

(ii) electron(s) are lost (from calcium atoms)

ignore numbers if given

do not accept any reference to oxygen

1

[7]

Q39.

(a) (i) hydrogen ions

1

(ii) partially ionised

1

(b) (i) burette

1

(ii) indicator

1

(iii) colour change or turns pink

1

(c) 20.4(0)

correct answer with or without working gains 2 marks

if answer incorrect allow

20.80 or

for 1 mark

2

(d) 50 (g)

correct answer with or without working gains 2 marks

if answer incorrect allow evidence of 1.25 × 40 for 1 mark

2

[9]

Q40.

(a) Hydrogen / H+

ignore state symbols

ignore proton / H

1

(b) it = weak acid

pH of weak acid is higher than the pH of a strong acid

allow converse for strong acids

allow correct numerical comparison

1

any one from:

allow converse for strong acids

• only partially dissociated (to form ions)

allow ionises less

• not as many hydrogen ions (in the solution)

allow fewer H+ released

1

(c) (i) (titration of) weak acid and strong base

1

(ii) 0.61

correct answer with or without working gains 2 marks

if the answer is incorrect:

moles of sodium hydroxide = (30.5 × 0.5)/1000 = 0.01525 moles

or

(0.5 × 30.5/25) gains 1 mark

2

(d) 12

correct answer with or without working gains 2 marks or even with incorrect working.

if the answer is incorrect:

0.8 × 60 = 48g

or

evidence of dividing 48g (or ecf) by 4

or

0.8 × 0.25 = 0.2 mol

or

evidence of multiplying 0.2mol (or ecf) by 60

would gain 1 mark

2

[8]

Q41.

(a) (i) conducts electricity

1

(ii) mixture (of metals)

(it = alloy)

1

(b) any two from:

ignore pollution without qualification

• noise

• dust

allow dirt

• traffic

• eyesore

2

[4]

Q42.

(a) (i) low percentage / very little of metal (in the ore)

accept only 0.5% metal in the ore or over 99% waste in the ore or nearly 100% waste in the ore

ignore reference to percentage of metal in the Earth's crust or energy used or pollution

1

(ii) any one from

(it = iron)

• iron uses less energy / fuel for extraction

ignore electrolysis / uses electricity / reactivity

• iron has more uses

• more demand for iron

ignore high abundance in the Earth’s crust / high percentage of metal in ore

• iron is stronger

ignore harder

• cheaper / costs less

• easier to extract

1

(b) (i) has melting point lower than 950°C

(it = aluminium)

allow has a low melting point

ignore boiling point

1

(ii) electrode(s) made of carbon

1

oxygen reacts with electrode(s) / carbon

accept C + O2 (→ CO2)

NB oxygen reacts with the carbon electrode(s) = 2 marks

1

(iii) any two from:

• saves resources / non-renewable

accept aluminium / ore will run out or conserves aluminium

• landfill problem

accept aluminium does not corrode

• saves energy / fuel / electricity

ignore global warming

• less carbon dioxide / carbon emissions or reduces carbon footprint

ignore consequences of quarrying / mining

• less quarrying / mining

ignore pollution / harms environment / costs / easy to recycle

2

[7]

Q43.

(a) (i) removal of oxygen

accept definition in terms of electrons or oxidation numbers

ignore oxides

1

(ii) 2 (Cl2)

allow correct multiples

1

(iii) no atoms are lost / made (during a chemical reaction)

or

the atoms are rearranged (during a chemical reaction)

accept because of (the law of) conservation of mass / matter

1

(b) (i) sodium is more reactive (than titanium)

accept sodium is very reactive or titanium is less reactive

do not accept sodium is more reactive than argon

1

(ii) any one from:

• sodium / titanium would react with oxygen / air

accept air / oxygen is reactive

• sodium / titanium does not react with argon

accept argon is unreactive / inert / a noble gas / in group O

1

(c) (i) all atoms are the same / it only contains one type of atom

accept all ions are the same

do not accept only got one atom

do not accept all atoms are the same size

ignore particles

1

(ii) two different / types atoms / elements / ions

accept more than one type of atom / ion / element

do not accept different size

1

bonded / joined together

accept definite proportions

do not accept mixture

1

[8]

Q44.

(a) diagram A

1

(b) the atoms can slide over each other.

1

the atoms are in layers

1

(c) (i) sulfuric

1

(ii) bubbles are produced

1

the magnesium disappears

1

(iii) crystallisation

1

[7]

Q45.

(a) the ions can move / travel / flow /are free

accept particles / they for ions

allow delocalised ions

or

ignore delocalised / free electrons

ignore references to collisions

accept converse with reference to solid

the ions carry the charge / current

ignore ions carry electricity

1

(b) any one from:

• because they are negative / anion

allow Cl–

ignore chlorine

• opposite charges / attract

1

(c) 13

1

(d) (i) reasonable attempt at straight line which misses the anomalous point

must touch all five crosses

do not allow multiple lines

1

(ii) 40

ignore 2.2

1

(iii) any two sensible errors from:

ignore systematic / human / apparatus / zero /experimental / random / measurement / reading errors unless qualified

• gas escapes

• weighing error

allow NaCl not measured correctly

• error in measuring (volume / amount) of hydrogen

• error in measuring (volume / amount) of water

allow error in measuring volume / scale for 1 mark if neither hydrogen or water mentioned

• incorrect concentration

allow NaCl not fully dissolved or spilled or impure

• timing error

• change in voltage / current

allow faulty power supply

• change in temperature

• recording / plotting error

2

(iv) any one from:

ignore ‘do more tests’

• repeat the experiment

• results compared with results from /other students / other groups / other laboratories / internet / literature.

• results compared with another method

1

(v) increases owtte

allow directly proportional or positive correlation

allow rate / it is faster / quicker

1

[9]

Q46.

(a) • made of layers / rows (atoms / ions / particles)

ignore free / delocalised electrons

1

• which can slide / slip (over each other)

reference to incorrect particles / covalency / intermolecular forces = max 1

or

particles / ions / atoms can slide over each other

ignore malleable / ductile / weak bonds

1

(b) (i) sulfuric

accept sulphuric

ignore formula

ignore hydrogen sulfate

1

(ii) any two from:

list principle applies for incorrect observations

• (hydrogen) gas produced (or any indication of a gas such as

bubbles etc.)

ignore just hydrogen produced

ignore cloudiness / colour changes

• magnesium / solid disappears / goes into solution

accept magnesium / magnesium sulfate / solid / it dissolves

accept forms a liquid / solution

• gets hot

allow exothermic

ignore floats

2

(iii) crystallisation

accept detailed answers such as: evaporate to half volume and then allow the solution to crystallise.

or

evaporation / heating / boiling / cooling

ignore any references to filter

1

[6]

Q47.

(a) (carbon =) 1

1

(oxygen =) 3

1

(b) (i) heated

1

(ii) carbon dioxide

1

(c) (i) combustion

1

(ii) carbon is more reactive than zinc

1

(iii) zinc boils (in the furnace / below 1300°C)

ignore melting point / changes of state

1

lead does not boil / (only) melts in the furnace / boils above 1300°C

if no other mark awarded allow zinc has a lower boiling point or lead has a higher boiling point

or they / zinc and lead have different boiling points for 1 mark

1

[8]

Q48.

(a) cannot move

1

(b) water

1

(c) (i) a positive charge

1

(ii) atoms

1

[4]

Q49.

(a) (i) electron(s)

allow free / delocalised / negative electrons

do not accept additional particles

1

(ii) ion(s)

allow named ions from table

ignore positive or negative

do not accept additional particles

1

(b) (i) copper

accept Cu

do not accept Cu2+

1

(ii) it is / they are positive (ions)

accept formula of positive ion

1

and it is the least reactive

1

(c) (i) loss of electron(s)

ignore numbers

1

(ii) 2H+ + 2e– → H2

accept correct multiples / fractions

accept e / e–

allow 2H+ → H2 – 2e–

1

[7]

Q50.

(a) (i) nitrogen - air

accept atmosphere

1

hydrogen - north sea gas / natural gas / methane / CH4

accept water / (crude) oil / coal / hydrocarbons / brine

1

(ii) allow converse throughout

• high temperature gives a low yield

1

• because reaction is exothermic

must be linked to first bullet point

1

• but at low temperatures the rate is (too) slow

if no other marks awarded accept 450°C is a compromise between yield and rate

or

450°C gives a reasonable yield in a reasonable time for 1 mark

1

(iii) nitric (acid)

accept HNO3

1

(b) Ammonia / Haber process can be used to make fertiliser

1

with a specified economical reason

eg raw materials for Haber process readily available

eg transport costs are lower or no need to import

eg Haber process is a continuous process

ignore employment / labour costs

1

[8]

Q51.

(a) (i) sodium hydroxide solution

1

blue

1

(ii) barium chloride

1

white

1

(b) fully ionised in water

1

(c) (i) H+ ions

1

(ii) lower than

1

(d) (i) (indicator) changed colour / goes colourless

ignore clear / discoloured

1

(ii) 13.9

or

(titration) 2

1

(iii) 13.2

ecf from (d)(ii)

1

[10]

Q52.

(a) (i) incorrect test or no test = 0 mark

testing the solution or using blue litmus = 0 mark

(test ammonia / gas with red) litmus

accept any acid-base indicator with correct result

1

(goes) blue

OR

(conc.) HCl (1)

white fumes / smoke / solid (1)

allow white gas / vapour

OR

(test ammonia / gas with) Universal Indicator (1)

blue / purple (1)

1

(ii) incorrect test or no test = 0 marks

add barium chloride / BaCl2 (solution)

do not accept H2SO4 added

or add barium nitrate / Ba(NO3)2 (solution)

allow Ba2+ solution / aqueous added

1

white precipitate / solid (formed)

allow white barium sulfate / BaSO4

ignore barium sulfate / BaSO4 alone

1

(b) (i) fully / completely ionised / dissociated

or hydrogen ions fully dissociated

accept has more ions than weaker acid / alkali of same concentration

ignore strongly ionised

do not accept ions are fully ionised

ignore concentrated or reference to concentrations of ions

1

(ii) methyl orange

accept correct spelling only

accept any strong acid-weak base indicator

do not allow phenolphthalein / litmus / universal indicator

1

(iii) 32 × 0.05/1000 or 0.0016 (mole H2SO4 )

accept (0.05 x 32) = (V x 25) or 0.05 x 32 / 25

1

(reacts with) 2 × 0.0016 or 0.0032 (mole NH3 in 25 cm3)

accept dividing rhs by 2 or multiplying lhs by 2

1

(0.0032 × 1000/25 =) 0.128

allow ecf from previous stage

correct answer 0.128 or 0.13 with or without working gains all 3 marks

1

(iv) 2.176 or 2.18

correct answer with or without working

or ecf from candidate’s answer to (b)(iii)

or 2.55 if 0.15 moles used

if answer incorrect or no answer

0.128 × 17 or 0.13 x 17

or their (b)(iii) × 17

or 0.15 × 17 gains 1 mark

2

[11]

Q53.

(a) (i) copper / Cu

1

(ii) 50(p)

1

(iii) 25

1

(iv) tin

1

(b) (i) any one from:

• high cost of copper

allow metal is expensive

• less copper available or (copper ores exhausted / only low-grade ores available)

allow copper is non-renewable

• high demand for copper

• high percentage (%) of copper in the coin

• inflation (of cost)

1

(ii) any one from:

• stronger / harder

ignore rust

• cost of copper or copper is more expensive to extract or steel is cheap

allow cheaper (to make)

• less copper available

or

(copper ores exhausted / only low-grade ores available)

• high demand for copper

• less copper is needed

1

[6]