Chemical Changes Mark schemes

Q1.

(a) Whether there was a reaction or not

1

(b) brown / orange / dark deposit on zinc

or

blue solution turns colourless / paler

1

(c) Variable Measuring instrument

more than one line drawn from a variable negates the mark

2

(d) (Most reactive) Magnesium

Zinc

(Least reactive) Copper

must all be correct

1

(e) would not be safe or

too reactive

allow too dangerous

1

(f) Gold

1

(g) 2Fe2O3 + 3C → 4Fe + 3CO2

allow multiples

1

(h) carbon

1

(i) Loss of oxygen

1

[10]

Q2.

(a) 36 cm3

1

(b) all points correct

± ½ small square

2

allow 1 mark if 6 or 7 of the points are correct

2 best fit lines drawn

must not deviate towards anomalous point

2

allow 1 mark if 1 line correct

(c) The bung was not pushed in firmly enough.

1

The measuring cylinder was not completely over the delivery tube.

1

(d) as mass of lithium carbonate increases volume of gas produced increases

1

linear / (directly) proportional

1

(e) A gas / carbon dioxide is produced.

allow because the air in the tube expands

1

(f) any one from:

• Potassium carbonate does not decompose to produce carbon dioxide / a gas.

• Potassium carbonate does not decompose at the temperature of the Bunsen

burner or the Bunsen burner is not hot enough to decompose potassium carbonate.

• When potassium carbonate decomposes a gas is not formed.

1

[11]

Q3.

(a) any two from:

• concentration / volume of dilute hydrochloric acid

• mass of metal powder

• surface area of metal powder

• stirring (of any) / rate of stirring

allow reacted for the same length of time

2

(b) 4.2 °C

allow Magnesium Test 2

1

and any one from:

• lower mass of magnesium added

• surface area of magnesium too low

• magnesium coated in magnesium oxide (so took a while to start reacting)

• not stirred

• not stirred as quickly as the other metals

• not reacted for as long a time as the other metals

allow reason for break in circuit

1

(c) 17.4(°C)

1

(d) bubbles of gas

1

more (bubbles) seen with calcium than other metals

allow any correct comparison between two metals

1

(e) any value between 7.9 °C and 12.3 °C

1

[8]

Q4.

(a) any one from:

• there was a flame

• energy was given out

• a new substance was formed

• the magnesium turned into a (white) powder

answers must be from the figure

1

(b) Magnesium oxide

1

(c) The reaction has a high activation energy

1

(d) 9

1

(e) They have a high surface area to volume ratio

1

(f) any one from:

• Better coverage

• More protection from the Sun’s ultraviolet rays

1

(g) any one from:

• Potential cell damage to the body

• Harmful effects on the environment

1

(h) indication of = 0.625

and

use of indices 10−9 − 10−6 = 103

Both steps must be seen to score first mark

1

0.625 × 1000 = 625 (times bigger)

1

[9]

Q5.

(a) s

1

l

Answers must be in the correct order.

1

(b) A gas was lost from the flask

1

(c) Level 3 (5–6 marks):

A coherent method is described with relevant detail, and in correct sequence which demonstrates a broad understanding of the relevant scientific techniques and procedures. The steps in the method are logically ordered. The method would lead to the production of valid results.

Level 2 (3–4 marks):

The bulk of the method is described with mostly relevant detail, which demonstrates a reasonable understanding of the relevant scientific techniques and procedures. The method may not be in a completely logical sequence and may be missing some detail.

Level 1 (1–2 marks):

Simple statements are made which demonstrate some understanding of some of the relevant scientific techniques and procedures. The response may lack a logical structure and would not lead to the production of valid results.

0 marks:

No relevant content.

Indicative content

• sulfuric acid in beaker (or similar)

• add copper carbonate one spatula at a time

• until copper carbonate is in excess or until no more effervescence occurs *

• filter using filter paper and funnel

• filter excess copper carbonate

• pour solution into evaporating basin / dish

• heat using Bunsen burner

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

• decant solution

• pat dry (using filter paper)

• wear safety spectacles / goggles

*Students. may choose to use a named indicator until it turns a neutral colour, record the number of spatulas of copper carbonate added then repeat without the indicator.

6

(d) Total mass of reactants = 221.5

1

159.5

221.5

allow ecf from step 1

1

72.0 (%)

1

allow 72.0 with no working shown for 3 marks

(e) any one from:

• Important for sustainable development

• Economic reasons

• Waste products may be pollutants / greenhouse gases

1

[13]

Q6.

(a) any one from:

• heat

• stir

1

(b) filter

accept use a centrifuge

accept leave longer (to settle)

1

(c) any one from:

• wear safety spectacles

• wear an apron

1

(d) evaporation at A

1

condensation at B

1

(e) 100

1

[6]

Q7.

(a) The forces between iodine molecules are stronger

1

(b) anything in range +30 to +120

1

(c) Brown

1

(d) 2 I− + Cl2 → I2 + 2 Cl−

1

(e) It contains ions which can move

1

(f) hydrogen iodine

1

[6]

Q8.

(a) add excess copper carbonate (to dilute hydrochloric acid)

accept alternatives to excess, such as ‘until no more reacts’

1

filter (to remove excess copper carbonate)

reject heat until dry

1

heat filtrate to evaporate some water or heat to point of crystallisation

accept leave to evaporate or leave in evaporating basin

1

leave to cool (so crystals form)

until crystals form

1

must be in correct order to gain 4 marks

(b) Mr CuCl2 = 134.5

correct answer scores 4 marks

1

moles copper chloride = (mass / Mr = 11 / 134.5) = 0.0817843866

1

Mr CuCO3= 123.5

1

Mass CuCO3 (=moles × M2= 0.08178 × 123.5) = 10.1(00)

1

accept 10.1 with no working shown for 4 marks

(c)

or

11.0 × 0.791

1

8.70 (g)

1

accept 8.70(g) with no working shown for 2 marks

(d) Total mass of reactants = 152.5

1

134.5

152.5

allow ecf from step 1

1

88.20 (%)

1

allow 88.20 with no working shown for 3 marks

(e) atom economy using carbonate lower because an additional product is made or carbon dioxide is made as well

allow ecf

1

[14]

Q9.

(a) (zinc has) lost electron(s)

accept loss of electrons

1

(b) copper is the least reactive

1

because it gave the most negative voltage when it was metal 2

or

it gave the biggest voltage with chromium

or

it gave the most positive voltage when it was metal 1

1

(c) −0.7 V

1

The voltage with chromium and copper is 1.2

accept use of other cell pairings such as tin with copper and tin with iron

1

The voltage with chromium and iron is 0.5 and copper is less reactive (than iron)

1

(d) hydrogen + oxygen = water

1

(e) H2 → 2H+ + 2e−

1

O2 + 4H+ + 4e− → 2H2O

1

[9]

Q10.

(a) (delivery) tube sticks into the acid

1

the acid would go into the water or the acid would leave the flask or go up the delivery

tube

ignore no gas collected

1

(b) any one from:

• bung not put in firmly / properly

• gas lost before bung put in

• leak from tube

1

(c) all of the acid has reacted

1

(d) take more readings in range 0.34 g to 0.54 g

1

take more readings is insufficient

ignore repeat

(e) 95

24000

1

0.00396

or

3.96 × 10−3

1

accept 0.00396 or 3.96 × 10−3 with no working shown for 2 marks

(f) use a pipette / burette to measure the acid

1

because it is more accurate volume than a measuring cylinder

or

greater precision than a measuring cylinder

or

use a gas syringe to collect the gas

so it will not dissolve in water

or

use a flask with a divider

accept description of tube suspended inside flask

so no gas escapes when bung removed

1

(g) they should be collected because carbon dioxide is left in flask at end

1

and it has the same volume as the air collected / displaced

1

[11]

Q11.

(a) (sulfuric acid is) completely / fully ionised

1

In aqueous solution or when dissolved in water

1

(b) H+(aq) + OH−(aq) → H2O(l)

allow multiples

1 mark for equation

1 mark for state symbols

2

(c) adds indicator, eg phenolpthalein / methyl orange / litmus added to the sodium hydroxide

(in the conical flask)

do not accept universal indicator

1

(adds the acid from a) burette

1

with swirling or dropwise towards the end point or until the indicator just changes colour

1

until the indicator changes from pink to colourless (for phenolphthalein) or yellow to red

(for methyl orange) or blue to red (for litmus)

1

(d) titrations 3, 4 and 5

or

1

27.12 cm3

accept 27.12 with no working shown for 2 marks

1

allow 27.1166 with no working shown for 2 marks

(e) Moles H2SO4 = conc × vol = 0.00271

allow ecf from 8.4

1

Ratio H2SO4:NaOH is 1:2

or

Moles NaOH = Moles H2SO4 × 2 = 0.00542

1

Concentration NaOH = mol / vol = 0.00542 / 0.025 = 0.2168

1

0.217 (mol / dm3)

accept 0.217 with no working for 4 marks

1

accept 0.2168 with no working for 3 marks

(f) × 0.18 = no of moles

or

0.15 × 40 g

1

0.144 (g)

1

accept 0.144g with no working for 2 marks

[16]

Q12.

(a) CaCO3 + 2HCl → CaCl2 + H2O + CO2

2

allow 1 mark for correct formulae

(b) sensible scales, using at least half the grid for the points

1

all points correct

± ½ small square

allow 1 mark if 8 or 9 of the points are correct

2

best fit line

1

(c) steeper line to left of original

1

line finishes at same overall volume of gas collected

1

(d) acid particles used up

allow marble / reactant used up

1

so concentration decreases

allow surface area of marble decreases

1

so less frequent collisions / fewer collisions per second

do not accept fewer collisions unqualified

1

so rate decreases / reaction slows down

1

(e) mass lost of 2.2 (g)

1

time taken of

270 s

allow values in range 265 − 270

1

allow ecf for values given for mass and time

1

0.00815 (g / s)

or

8.15 × 10−3

allow 1 mark for correct calculation of value to 3 sig figs

accept 0.00815 or 8.15 × 10−3 with no working shown for 4 marks

1

(f) correct tangent

1

eg 0.35 / 50

1

0.007

allow values in range of 0.0065 − 0.0075

1

7 × 10−3

1

accept 7 × 10−3 with no working shown for 4 marks

[20]

Q13.

(a) (i) (thermal) decomposition

allow decomposes or endothermic

1

(ii) copper oxide

1

(b) (i) the (potassium) carbonate did not decompose/change/react (when heated)

allow temperature not high enough

do not allow potassium did not decompose

ignore references to reactivity

1

the mass did not change or the limewater did not go cloudy

1

because no carbon dioxide produced

1

(ii) the less reactive the metal the more (easily) its carbonate will decompose/react or vice versa

needs to be a relative comparison

2

allow max 1 mark where the distinction between a metal and its carbonate is not clear

allow 1 mark for carbonates of reactive metals do not decompose or vice versa

(c) (i) make it economical (to extract the metal/iron)

allow make it worth extracting

allow so they can make money/profit

1

(ii) Fe

1

balanced correctly (2,3,4,3)

not ecf

allow correct balanced equation but with 2Fe2 on right for one mark

1

(iii) iron from the blast furnace is brittle

1

steel produced is strong / flexible

allow steel has more/specific uses

allow steel is rust-resistant

1

“it” = iron

(iv) (recycling) is used to conserve iron (ore) or energy or resources or minimise pollution or reduce the need to quarry

allow reverse arguments.

1

(not reuse) because of damage, paint removal, rusting/corrosion, metal fatigue/weaker

1

(not landfill) because sites have limited space or loss of habitats

allow to reduce the use of landfill

1

[15]

Q14.

(a) electricity

allow an electric current

1

(b) (i) chlorine/Cl2

do not accept chloride

1

(ii) (zinc ions are) positive

ignore to gain electrons

1

and (opposite charges) attract

1

(iii) reduction

1

(c) (i) in alloy:

accept converse

different sized atoms/particles

or

no layers/rows

accept layers distorted

1

so cannot slide

1

(ii) shape memory (alloys)

accept smart

1

[8]

Q15.

(a) sulfur dioxide

accept SO2

1

(b) (i) curved line of best fit between the 4 non-anomalous points

1

(ii) temperature was lower (than 40 °C)

accept student missed the moment when the cross disappeared

accept smaller volume of acid or acid more dilute

1

(iii) 0.005 or 1/200

correct answer with or without working gains 2 marks

if answer incorrect, allow 1 mark for 0.32 / 64

2

(iv) The particles move faster.

1

The particles collide with more energy.

1

(v) activation

1

[8]

Q16.

(a) endothermic

1

(b) 82 (%)

correct answer with working gains 3 marks

if 17 or 34 not shown in working max 2 marks

accept 82.4

accept 82.35 to full calculator display (82.35294...) correctly rounded to at least 2 sf

if no answer or incorrect answer, then

(Mr =) 17 gains 1 mark or

14/17 gains 2 marks

OR

(2Mr =) 34 gains 1 mark or

28/34 gains 2 marks

OR

14/their Mr shown gains 1 mark or

correct calculation of 14/their Mr gains 2 marks

3

(c) (i) 7 / seven

1

(ii) H+ + OH– → H2O

1

(iii) ammonium chloride

allow NH4Cl

1

ignore an incorrect formula

(d) 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.

Level 3 (5 – 6 marks):

Suggestion with reasons from all three graphs, and linking of ideas which may explain a compromise.

Level 2 (3 – 4 marks):

Suggestion with reasons referring to more than one graph.

Level 1 (1 – 2 marks):

Suggestion with a reference to a graph.

0 marks:

No relevant content.

Examples of chemistry points made in response:

A reasonable suggested amount of fertiliser would be in the region of 200 kg (per ha).

Accept any suggestion from about 180 kg (per ha) to 500 kg (per ha).

Yield:

• Using fertiliser improves yield.

• Yield improved most up to about 200 kg (per ha) of fertiliser.

• Yield only increased slightly above about 200 kg (per ha).

Profit:

• About 200 kg of fertiliser gives the most profit.

• Above about 200 kg (per ha) of fertiliser profit declines.

Run off:

• Run off is at low levels until about 300 kg (per ha) of fertiliser.

• Above about 300 kg (per ha) of fertiliser, run off increases.

Examples of linking of ideas:

• Overall 200 kg gives high crop yield and most profit.

• In conclusion 200 kg gives high crop yield and low run off.

• 200 kg gives most profit and low run off.

Examples of compromise:

• Profits go down after about 200 kg (per ha) of fertiliser because cost of fertiliser is not covered by increased yield.

• 200 kg gives the highest profit although it is not the highest yield.

• 500 kg gives the best yield but has the most runoff.

6

[13]

Q17.

(a) because sulfur / S (forms)

1

(which) is solid / insoluble / a precipitate / a suspension

1

(b) any two from:

• volume of sodium thiosulfate

ignore amount of sodium thiosulfate

• volume of (hydrochloric) acid

ignore amount of (hydrochloric) acid

• concentration of sodium thiosulfate

• concentration of (hydrochloric) acid

if no other mark, allow 1 mark for same cross or same flask or unspecified volume or unspecified concentration

ignore same person

do not accept references to temperature

2

(c) rate increases

1

because particles move faster

accept particles have more energy

1

so frequency of collisions increases

accept particles are more likely to collide or more chance of collisions

ignore more collisions

1

more particles / collisions have energy greater than (or equal to) the activation energy

1

(d) cool

accept refrigerate or method to decrease temperature

or

decrease the temperature (of the solutions)

1

[9]

Q18.

(a) magnesium loses two electrons and chlorine gains one electron

accept magnesium loses electrons and chlorine gains electrons for 1 mark

ignore oxidation and reduction

2

one magnesium and two chlorines

accept MgCl2

1

noble gas structure

or

eight electrons in the outer shell

accept full outer shell (of electrons)

or

(electrostatic) attraction between ions

or

forms ionic bonds

do not accept covalent bonds

1

reference to incorrect particles or incorrect bonding or incorrect structure = max 3

(b) (i) because ions can move

ignore ions attracted

do not accept molecules / atoms moving

do not accept incorrect reference to electrons moving

1

(and ions move) to the electrodes

or

(and ions) carry charge

1

accept converse for solid

(ii) magnesium (ions) attracted (to the electrode)

1

so magnesium ions gain electrons

accept magnesium ions are reduced

ignore oxidised

1

2 electrons

accept a correct half equation for 2nd and 3rd marking points

1

(iii) hydrogen

allow H2

1

(iv) magnesium is more reactive than hydrogen

accept converse

allow magnesium is high in the reactivity series or magnesium is very/too reactive.

do not accept magnesium ions are more reactive than hydrogen ions

1

(v) 2 Cl- → Cl2 + 2e-

must be completely correct

1

(c) layers (of particles/atoms/ions)

1

(particles/atoms/ions/layers) can slide

1

any mention of intermolecular / weak bonds/forces = max 1

[14]

Q19.

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.

Level 3 (5 – 6 marks)

There is a description of titrations that would allow a comparison to be made between the two solutions of hydrochloric acid.

Level 2 (3 – 4 marks)

There is a description of an experimental method including addition of acid to alkali which may include an indicator or colour change and may include a measurement of volume.

Level 1 (1 – 2 marks)

There is a simple description of using some of the apparatus.

0 marks

No relevant content.

examples of chemistry points made in the response could include:

• acid in burette or flask

• alkali/sodium hydroxide or acid in burette or flask

• volume of acid or alkali measured using the pipette

• indicator in flask

• white tile under the flask

• slow addition

• swirling/mixing

• colour change of indicator

• burette volume measured

[6]

Q20.

(a) (i) neutrons

this order only

1

electrons

1

protons

1

(ii) box on the left ticked

1

(b) (i) effervescence / bubbling / fizzing / bubbles of gas

do not accept just gas alone

1

magnesium gets smaller / disappears

allow magnesium dissolves

allow gets hotter or steam produced

ignore references to magnesium moving and floating / sinking and incorrectly named gases.

1

(ii) Marks awarded for this answer will be determined by the Quality of Communication (QC) as well as the standard of the scientific response. Examiners should also refer to the information in the Marking Guidance and apply a ‘best–fit’ approach to the marking.

0 marks

No relevant content

Level 1 (1−2 marks)

There are simple statements of some of the steps in a procedure for obtaining magnesium chloride.

Level 2 (3−4 marks)

There is a description of a laboratory procedure for obtaining magnesium chloride from dilute hydrochloric acid and magnesium.

The answer must include a way of ensuring the hydrochloric acid is fully reacted or a method of obtaining magnesium chloride crystals.

Level 3 (5−6 marks)

There is a well organised description of a laboratory procedure for obtaining magnesium chloride that can be followed by another person.

The answer must include a way of ensuring the hydrochloric acid is fully reacted and a method of obtaining magnesium chloride crystals.

examples of the points made in the response:

• hydrochloric acid in beaker (or similar)

• add small pieces of magnesium ribbon

• until magnesium is in excess or until no more effervescence occurs *

• filter using filter paper and funnel

• filter excess magnesium

• pour solution into evaporating basin / dish

• heat using Bunsen burner

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

• decant solution

• pat dry (using filter paper).

*Student may choose to use a named indicator until it turns a neutral colour, record the number of pieces of magnesium added then repeat without the indicator.

6

[12]

Q21.

(a) (i) calcium oxide

in either order

1

carbon dioxide

accept correct formulae

1

(ii) C(s) + CO2(g) → 2CO(g)

allow multiples

1

(iii) 210 (tonnes)

award 3 marks for the correct answer with or without working

allow ecf for arithmetical errors

if answer incorrect allow up to 2 marks for any of the steps below:

160 → 112

300 → 112 / 160 × 300

or

moles Fe2O3 = 1.875 (× 106) or 300 / 160

moles of Fe = 3.75 (× 106) or 2 × moles Fe2O3

mass Fe = moles Fe × 56

105 (tonnes) scores 2 (missing 1:2 ratio)

420 (tonnes) scores 2 − taken Mr of iron as 112

3

(b) (i) aluminium is more reactive than carbon or carbon is less reactive than aluminium

must have a comparison of reactivity of carbon and aluminium

accept comparison of position in reactivity series.

1

(ii) (because) aluminium ions are positive

ignore aluminium is positive

1

and are attracted / move / go to the negative electrode / cathode

1

where they gain electrons / are reduced / Al3+ + 3e− → Al

accept equation or statements involving the wrong number of electrons.

1

(iii) (because) the anodes or (positive) electrodes are made of carbon / graphite

1

oxygen is produced (at anode)

1

which reacts with the electrodes / anodes

do not accept any reference to the anodes reacting with oxygen from the air

equation C + O2 CO2 gains 1 mark (M3)

1

[13]

Q22.

(a) 31

1

(b) (i) any two from:

• incorrect reading of thermometer / temperature

• incorrect measurement of volume of acid

• incorrect measurement of volume of alkali (burette).

2

(ii) glass is a (heat) conductor or polystyrene is a (heat) insulator

answer needs to convey idea that heat lost using glass or not lost using polystyrene

accept answers based on greater thermal capacity of glass (such as “glass absorbs more heat than polystyrene”)

1

(c) (i) temperature increases

1

(ii) no reaction takes place or all acid used up or potassium hydroxide in excess

1

cool / colder potassium hydroxide absorbs energy or lowers temperature

ignore idea of heat energy being lost to surroundings

1

(iii) take more readings

ignore just “repeat”

1

around the turning point or between 20 cm3 and 32 cm3

accept smaller ranges as long as no lower than 20 cm3 and no higher than 32 cm3

1

(d) 1.61 or 1.6(12903)

correct answer with or without working scores 3

if answer incorrect, allow a maximum of two from:

moles nitric acid = (2 × 25 / 1000) = 0.05 for 1 mark

moles KOH = (moles nitric acid) = 0.05 for 1 mark

concentration KOH = 0.05 / 0.031

answer must be correctly rounded (1.62 is incorrect)

3

(e) same amount of energy given out

1

which is used to heat a smaller total volume or mixture has lower thermal capacity

or

number of moles reacting is the same

but the total volume / thermal capacity is less

if no other marks awarded award 1 mark for idea of reacting faster

1

[14]

Q23.

(a) gold

1

(b) atom (s)

1

(c) (i) protons

any order

allow proton

1

neutrons

allow neutron

1

(ii) 3 / three

1

(d) (i) Al

ignore any numbers / charges

1

(ii) any two from:

• limited resource

• expensive in terms of energy / mining

• effects on the environment, such as, landfill, atmospheric pollution, quarrying

allow uses a lot of energy to extract.

2

(e) resistant to corrosion

1

does not react (with water or food)

allow one mark for low density with a suitable reason given

1

[10]

Q24.

(a) The ore is not pure or contains impurities or the ore does not contain 100% of the metal compound

allow to concentrate the metal or metal compound

1

rock / other compounds need to be removed / separated

1

(b) (i) (cast iron is) brittle

allow not strong

ignore weak

1

(ii) the oxygen reacts with carbon

allow carbon burns in oxygen or is oxidised

1

reducing the percentage of carbon in the mixture

or producing carbon dioxide

1

(c) (i) aluminium has a low density

1

(ii) (because copper) is in the central / middle (block of the periodic table)

1

whereas aluminium is in Group 3 (of the periodic table)

1

(iii) iron is more reactive (than copper)

ignore cost

1

so copper is displaced / reduced

1

[10]

Q25.

(a) sodium loses (electron)

sharing / covalent / metallic = max 2

1

chlorine gains (electron)

1

1 or an (electron)

1

(b) (i) Have no overall electric charge

1

(ii) Should iodine be added to salt?

1

reason

any one 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.

1

(c) (i) nitric (acid)

1

(ii) an alkali

1

(iii) indicator

accept any named acid base indicator

1

(d) (i) Crystallisation

1

(ii) fertiliser

allow to help crops grow

1

(iii) any one from:

• pressure

allow concentration

• temperature

ignore heat

• catalyst.

1

[12]

Q26.

(a) any one from:

• protection / improve lifespan

• improve appearance.

1

(b) (i) Bleach

1

(ii) Hydrogen is less reactive than sodium

1

(iii) 1 bonding pair of electrons 6 unbonded electrons on Cl

accept dot, cross or e or − or any combination

1

(iv) Covalent

1

(v) Hydrogen chloride has a low boiling point.

1

Hydrogen chloride is made of simple molecules.

1

(c) (i) oxygen

accept carbon dioxide

1

(ii) aluminium ions are positive

1

so are attracted (to the negative electrode)

allow opposites attract

1

(iii) Reduction

1

(iv) slide

allow move

1

(d) (i) C

1

(ii) strong covalent bonds

1

[14]

Q27.

(a) any one from:

• solution becomes colourless or colour fades

• zinc becomes bronze / copper coloured

allow copper (forms) or a solid (forms)

• zinc gets smaller

allow zinc dissolves

• bubbles or fizzing.

ignore precipitate

1

(b) improvement:

use a plastic / polystyrene cup or add a lid

accept use lagging / insulation

1

reason - must be linked

reduce / stop heat loss

OR

improvement:

use a digital thermometer

allow use a data logger

reason - must be linked

more accurate or easy to read or stores data

allow more precise or more sensitive

ignore more reliable

ignore improvements to method, eg take more readings

1

(c) 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 and apply a ‘best–fit’ approach to the marking.

0 marks

No relevant content

Level 1 (1−2 marks)

There is a statement about the results.

Level 2 (3−4 marks)

There are statements about the results. These statements may be linked or may include data.

Level 3 (5−6 marks)

There are statements about the results with at least one link and an attempt at an explanation.

Examples of chemistry points made in the response:

Description:

Statements

Concentration of copper sulfate increases

Temperature change increases

There is an anomalous result

The temperature change levels off

Reaction is exothermic

Linked Statements

Temperature change increases as concentration of copper sulfate increases

The temperature change increases, and then remains constant

After experiment 7 the temperature change remains constant

Statements including data

The trend changes at experiment 7

Experiment 3 is anomalous

Attempted Explanation

Temperature change increases because rate increases

Temperature change levels off because the reaction is complete

Explanation

As more copper sulfate reacts, more heat energy is given off

Once copper sulfate is in excess, no further heat energy produced

6

[9]

Q28.

(a) giant structure / lattice / layers / close packed

first 3 marks can be obtained from a suitably labelled diagram

incorrect structure or bonding or particle = max 3

1

made up of atoms / positive ions

1

with delocalized / free electrons

1

so electrons can move / flow through the metal

accept so electrons can carry charge through the metal

accept so electrons can form a current

1

(b) an alloy (is a metal which) has different types / sizes of atoms

accept converse for pure metal throughout

both marks can be obtained from suitable diagrams

allow made of different metals

allow mixture of metals / atoms / elements

ignore particles

ignore properties

do not accept compound

1

alloy has distorted layers

allow layers are unable to slide

1

(c) (i) can return to its original shape

accept shape memory alloy

accept smart alloy

ignore other properties

1

(ii) (pure copper is too) soft

accept converse

accept malleable or bends

accept copper is running out

ignore references to strength and weakness

1

(iii) aluminium oxide

accept alumina

accept Al2O3

ignore bauxite / aluminium ore

1

(iv) any one from:

• different conditions

• different catalyst

• different pressure

allow different concentration

• different temperature.

do not accept different monomers

1

(d) any two from:

• accurate

• sensitive

• rapid

• small sample.

both needed for 1 mark

1

[11]

Q29.

(a) (i) silver nitrate

allow AgNO3

1

(ii) potassium carbonate or

allow K2CO3

sodium carbonate

allow Na2CO3

1

(b) base

allow ionic

ignore insoluble or soluble

ignore alkali

1

(c) (i) evaporate

or

crystallise

allow heat or boil or leave (to evaporate)

allow cool

ignore filtration unless given as an alternative

do not accept freeze or solidify

1

(ii) 2 (HNO3)

accept multiples

1

(iii) 9

accept nine

1

(d) 6.21 / 207 0.72 / 16

1 mark for dividing mass by Ar

1

= 0.03 = 0.045

1 mark for correct proportions (allow multiples)

1

2 3

1 mark for correct whole number ratio (allow multiples). Can be awarded from formula.

1

Pb2O3

allow O3Pb2

ecf allowed throughout if sensible attempt at step 1

correct formula with no working gains 1 mark

1

[10]

Q30.

(a) lattice / giant structure

max 3 if incorrect structure or bonding or particles

1

ionic or (contains) ions

1

Na+ and Cl-

accept in words or dot and cross diagram: must include type and magnitude of charge for each ion

1

electrostatic attraction

allow attraction between opposite charges

1

(b) hydrogen

allow H2

1

sodium hydroxide

allow NaOH

1

(c) any one from, eg:

• people should have the right to choose

• insufficient evidence of effect on individuals

• individuals may need different amounts.

allow too much could be harmful

ignore religious reasons

ignore cost

ignore reference to allergies

1

(d) (i) one bonding pair of electrons

accept dot, cross or e or − or any combination, eg

1

6 unbonded electrons on each atom

1

(ii) simple molecules

max 2 if incorrect structure or bonding or particles

accept small molecules

accept simple / small molecular structure

1

with intermolecular forces

accept forces between molecules

must be no contradictory particles

1

which are weak or which require little energy to overcome − must be linked to second marking point

reference to weak covalent bonds negates second and third marking points

1

(iii) iodine has no delocalised / free / mobile electrons or ions

1

so cannot carry charge

if no mark awarded iodine molecules have no charge gains 1 mark

1

[14]

Q31.

(a) (i) (19.5 + 18.5 + 19.0) / 3

allow (23.0 + 19.5 + 18.5 + 19.0) / 4 for 1 mark

2

(ii) R P Q

allow Q P R for 1 mark

2

(b) any two from:

• repeat more times

• calculate a mean

• measure to one decimal place.

2

(c) both students get similar results / similar pattern

1

[7]

Q32.

(a) any two from:

• fuel

allow source of energy

• solvent

allow perfume / aftershave

• antiseptic

allow antibacterial

2

(b) Hydrogen

1

(c) (i) oxidation

do not allow redox

1

(ii) correct structure

1

(iii) ethanoic acid is a weak / weaker acid

it = ethanoic acid

1

because it does not completely ionise.

allow because it does not completely dissociate

allow it has a lower concentration of hydrogen ions

allow converse for hydrochloric acid

do not allow ionising

1

(d) (i) ethyl ethanoate

1

(ii) acid

allow any strong acid

allow correct formulae

1

(iii) evaporates easily / quickly

allow low boiling point

do not allow flammable

1

[10]

Q33.

(a) X:

Fe2+ / iron(II), SO42- / sulfate

allow iron(II) sulfate

or FeSO4

1

Y:

Na+ / sodium, I- / iodide

allow sodium iodide

or NaI

1

Z:

Fe3+ / iron(III), Br- / bromide

allow iron(III) bromide

or FeBr3

correct identification of any two ions = one mark

correct identification of any four ions = two marks

1

(b) any five from:

allow converse arguments

method 1

• weighing is accurate

• not all barium sulfate may be precipitated

• precipitate may be lost

• precipitate may not be dry

• takes longer

• requires energy

allow not all the barium hydroxide has reacted

method 2

• accurate

• works for low concentrations

allow reliable / precise

5

[8]

Q34.

(a) (i) iron

either order

1

carbon dioxide

1

(ii) reduced

1

(b) (i) Statemant Explanation

each correct line gains 1 mark

extra lines from statement negate the mark

max. 2

(ii) the layers / rows are distorted / disrupted or it doesn’t occur in layers or the atoms are different

1

so cannot slide over one another or slide less easily

1

[7]

Q35.

(a) any two from:

• temperature (of the HCl)

• mass or length of the magnesium

• surface area of the magnesium

• volume of HCl

2

(b) (i) (a greater concentration has) more particles per unit volume

allow particles are closer together

1

therefore more collisions per unit time or more frequent collisions.

1

(ii) particles move faster

allow particles have more (kinetic) energy

1

therefore more collisions per unit time or more frequent collisions

1

collisions more energetic (therefore more collisions have energy greater than the activation energy) or more productive collisions

1

(c) (i) add (a few drops) of indicator to the acid in the conical flask

allow any named indicator

1

add NaOH (from the burette) until the indicator changes colour or add the NaOH dropwise

candidate does not have to state a colour change but penalise an incorrect colour change.

1

repeat the titration

1

calculate the average volume of NaOH or repeat until concordant results are obtained

1

(ii) moles of NaOH

0.10 × 0.0272 = 0.00272 moles

correct answer with or without working gains 3 marks

1

Concentration of HCl

0.00272 / 0.005 = 0.544

allow ecf from mp1 to mp2

1

correct number of significant figures

1

[14]

Q36.

(a) Sulfur dioxide causes acid rain.

1

(b) red / orange / yellow

do not accept any other colours

1

because sulfur dioxide (when in solution) is an acid

1

(c) (there are) weak forces (of attraction)

do not accept any reference to covalent bonds breaking

1

between the molecules

do not accept any other particles

1

(these) take little energy to overcome

award third mark only if first mark given

1

(d) Marks awarded for this answer will be determined by the Quality of Communication (QC) as well as the standard of the scientific response. Examiners should also refer to the information on page 5 and apply a ‘best-fit’ approach to the marking.

0 marks

No relevant content

Level 1 (1 – 2 marks)

A relevant comment is made about the data.

Level 2 (3 – 4 marks)

Relevant comparisons have been made, and an attempt made at a conclusion.

Level 3 (5 – 6 marks)

Relevant, detailed comparisons made and a justified conclusion given.

examples of the points made in the response

effectiveness

• W removes the most sulfur dioxide

• D removes the least sulfur dioxide

material used

• Both W and D use calcium carbonate

• Calcium carbonate is obtained by quarrying which will create scars on landscape / destroy habitats

• D requires thermal decomposition, this requires energy

• D produces carbon dioxide which may cause global warming / climate change

• S uses sea water, this is readily available / cheap

waste materials

• W product can be sold / is useful

• W makes carbon dioxide which may cause global warming / climate change

• D waste fill landfill sites

• S returned to sea / may pollute sea / easy to dispose of

6

[12]

Q37.

(a) (i) precipitation

1

(ii) (aq) on left hand side

1

(s) on right hand side

1

(iii) potassium iodide

1

potassium nitrate

1

(iv) filtration

1

(b) (i) diffusion

1

(ii) iodide ions move / diffuse faster than lead ions or travel further in the same time

Must be a comparison

Accept converse

1

because the lead iodide forms much closer to the lead nitrate (or X) than the potassium iodide (or Y).

allow because iodide ions are smaller than lead ions

allow references to potassium iodide and lead nitrate

1

(iii) the particles / ions move / diffuse faster

ignore which particles / ions the student refers to

1

because they have more energy or will collide / meet sooner

ignore reference to frequency of collisions

1

[11]

Q38.

(a) (i) points correctly plotted ( ± ½ small square)

four points = 2 marks

three points = 1 mark

Max 2

straight line of best fit using full range of points from 0,0

1

(ii) any one from:

must explain why the point is below the line

• the solution may not have been properly stirred

• the electrodes may have been a larger distance apart

• the drop of sodium chloride may have been a smaller volume / smaller

allow not enough sodium chloride added

allow smaller amount of sodium chloride

do not allow too few drops added

ignore the student may have misread the conductivity meter

1

(iii) any one from:

• the volume of pure water

allow amount

• the concentration (of the solutions added)

• the volume (of the drops) of solution added

ignore number of drops

• the distance between the electrodes

• the same electrodes or electrodes made of the same material

• same depth or surface area of electrodes in the water

• constant power supply

ignore current

• stirred

1

(b) (i) because (pure) water is covalent / molecular (simple) or contains molecules

1

therefore (pure) water has no free / mobile electrons or ions

molecules do not have a charge or molecules do not contain ions gains 2 marks

1

(ii) because there are ions in sodium chloride

allow Na+ and / or Cl–(ions) or ionic bonding.

Ignore particles other than ions for MP1.

1

which can move or carry the current / charge

MP2 must be linked to ions only.

1

(iii) Hydrogen

allow H2 / H

1

[10]

Q39.

(a) (i) any one from:

• one electron in the outer shell / energy level

• form ions with a 1+ charge

1

(ii) any one from:

• hydrogen is a non-metal

• (at RTP) hydrogen is a gas

• hydrogen does not react with water

• hydrogen has only one electron shell / energy level

• hydrogen can gain an electron or hydrogen can form a negative / hydride / H–ion

• hydrogen forms covalent bonds or shares electrons

accept answers in terms of the Group 1 elements

1

(b) (i) (bromine) gains electrons

it = bromine

do not accept bromide ion gains electrons

ignore loss of oxygen

1

(ii) I2

must both be on the right hand side of the equation

1

+ 2e–

2I– – 2e– ➔ I2 for 2 marks

1

(iii) fluorine is the smallest atom in Group 7 or has the fewest energy levels in Group 7 or has the smallest distance between outer shell and nucleus

the outer shell must be mentioned to score 3 marks

1

fluorine has the least shielding or the greatest attraction between the nucleus and the outer shell

1

therefore fluorine can gain an electron (into the outer shell) more easily

1

[8]

Q40.

(a) (i) copper is less reactive than hydrogen or copper is unreactive

1

(ii) Zinc and dilute hydrochloric acid

1

(b) (gas) syringe

1

(c) (i) 35

allow 3

1

because not close to others

accept it is much lower than the others

ignore references to trends or patterns

dependent on the first mark

1

(ii) (49 + 50 + 48) / 3

= 49

correct answer with or without working gains 2 marks

1

allow ecf from anomaly identified in (i) for 2 marks:

• Exp 1 anomalous gives 43.3

• Exp. 2 anomalous gives 44

• Exp. 4 anomalous gives 44.7

answer of 45.5 or 46 (anomaly not excluded) gains 1 mark

correct working excluding anomaly but with wrong answer gains 1 mark

1

(iii) so that a mean can be calculated

accept improves accuracy of the mean or so anomalies can be identified / discarded or to reduce effect of random errors

ignore makes it a fair test

ignore reliability, validity, repeatability, reproducibility

1

(d) (i) idea of mixing with oxygen / air, letting air / oxygen in

accept converse

1

(ii) H2O

do not accept incorrect additional products

1

balancing 2 … (1) … 2

allow fractions or multiples

dependent on first mark

1

[11]

Q41.

(a) any three from:

• concentration of (salt) solution

• volume of (salt) solution

ignore amount of solution

• initial temperature (of the solution)

ignore room temperature

• surface area / form of metal

• moles of metal

allow mass / amount

ignore time

ignore size of tube

3

(b) 20

1

32

1

12

allow ecf

1

(c) (i) four bars of correct height

tolerance is + / - half square

3 correct for 1 mark

2

bars labelled

1

(ii) one variable is non-continuous / categoric

accept qualitative or discrete

accept no values between the metals

1

(iii) magnesium

1

because biggest temperature change

accept gives out most energy

ignore rate of reaction

dependent on first mark

1

(iv) does not react / silver cannot displace copper

1

because silver not more reactive (than copper) or silver below copper in reactivity series

do not accept silver is less reactive than copper sulfate

1

(v) replace the copper sulfate

could be implied

1

with any compound of a named metal less reactive than copper

allow students to score even if use an insoluble salt

1

[16]

Q42.

(a) pure copper is twice as good a conductor as 99% pure copper

accept reverse argument

accept answers quoting 2 correct values from the graph scores 2

qualitative answer (e.g. pure copper is a better conductor than impure copper) scores 1

or

answers quoting a conductivity value from the graph scores 1

2

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

0 marks

No relevant content

Level 1 (1–2 marks)

Simple list of a limited number of points given, with no linking between ideas

Level 2 (3–4 marks)

A broader set of points made. There will probably not be links between ideas

Level 3 (5–6 marks)

Answer includes linking between ideas, showing the consequence of either not recycling or the advantage of recycling. Answers such as less fossil fuel needed so less carbon dioxide produced or less carbon dioxide produced so less global warming

examples of the points made in the response

resources

(recycling) conserves supplies of ores

copper available for longer

as (at present rate of use) copper ores will run out in about 35 years

(recycling) conserves supplies of fossil fuels or energy

less fuel used at a lower cost

land pollution

mining scars landscape or produces noise pollution

mining destroys wildlife habitats

(recycling) less need to mine ores / fossil fuels

so less habitat destroyed or less scarring of landscape

(recycling) less need to use landfill for waste

atmospheric pollution

burning fossil fuels produces carbon dioxide / greenhouse gas

which (may) cause global warming or climate change

extraction produces sulfur dioxide

which causes acid rain

which can kill trees / fish

6

(c) grow plants

accept plants absorb copper (through roots)

1

then plants are burned

1

ash (from burning) contains copper compounds

1

[11]

Q43.

(a) neutralisation

ignore reference to exothermic or endothermic

1

(b) 2 HCl + CaO ➔ CaCl2 + H2O

accept multiples and fractions

formulae

ignore state symbols

1

balancing (dependent on first mark)

1

(c) (the carbonate has) fizzing / bubbles / effervescence

ignore dissolving

ignore gas produced

1

(d) add excess calcium carbonate to acid (and stir) / add CaCO3 until fizzing stops

ignore heating the acid

accept answer using calcium oxide in place of calcium carbonate

1

(remove excess calcium carbonate by) filter(ing)

1

warm until a saturated solution forms / point of crystallisation / crystals start to form

do not accept heat until all water gone

1

leave to cool

dependent on previous mark

If solution not heated allow leave to evaporate (1)

until crystals form (1)

1

(e) (i) white precipitate / solid (forms)

1

insoluble in excess or remains or no (further) change in excess

dependent on a precipitate / solid forming

1

(ii) same result with magnesium (ions)

do not accept reference to any other ion(s) that do not give a white precipitate

accept other named ions that do give a white precipitate

1

(iii) flame test or description of flame test

1

gives a red flame

accept brick red or orange-red or scarlet

do not accept crimson

1

[13]

Q44.

(a) (i) economical

1

(ii) phytomining

1

(iii) carbon dioxide

1

(b) (i) copper / Cu

1

iron sulfate / FeSO4

1

(ii) copper / ions have a positive charge

it = copper ions

allow copper ions have a different charge

accept copper / ions are free to move

accept to gain electrons

accept copper / ions are attracted to the negative electrode or opposite charges attract

1

(c) any two from:

ignore not biodegradable or does not decay

• copper ores are limited / running out

allow copper is running out

• copper can be recycled

• copper can be reused

• copper is expensive

• landfill sites are filling up

• copper compounds are toxic

allow copper is toxic

2

[8]

Q45.

(a) (i) 14

1

(ii) isotope

1

(iii) (very) small

accept smaller / tiny / (very) little

1

(b) (i) C

1

(ii) NH3

1

(c) (i) nitric (acid)

1

(ii) indicator

1

(iii) crystallisation or evaporation

allow by heating or cooling or leave (on windowsill)

do not accept freezing

1

(iv) any one from:

• grass grows faster

• grass grows taller or thicker

allow grass grows better / greener

1

(d) potassium (atom) loses (an electron)

reference to incorrect bonding or particle = max 3

1

chlorine (atom) gains (an electron)

ignore references to full outer shells

1

1 (electron)

1

electron

1

[13]

Q46.

(a) (i) ions cannot move

allow only conducts as a liquid

1

(ii) chlorine

1

(iii) they are positively / oppositely charged

or

they are attracted

1

(iv) 2

1

(b) (i) any one from:

• not all the magnesium was collected

allow some magnesium was lost

• used less time or lower current or different battery / power pack or different balance or lower voltage

• error in reading balance

• error in recording result

1

(ii) 1.11

correct answer with or without working gains 2 marks.

if answer incorrect, allow 1 mark for 0.99

or for 1.13 + 1.11 + 1.09

2

(c) (i) 25 – 25.3

correct answer with or without working gains 2 marks.

If answer incorrect, allow 1 mark for 24 / 95

2

(ii) 71

1

(d) (i) reversible reaction

1

(ii) decreases

1

[12]

Q47.

(a) (i) (phosphoric) acid

allow phosphoric

1

(ii) H+ / hydrogen (ion)

if ion symbol given, charge must be correct

1

(b) (i) pencil

1

so it will not run / smudge / dissolve

ignore pencil will not interfere with / affect the results

or

because ink would run / smudge / dissolve

ignore ink will interfere with / affect the results

1

(ii) any three from:

reference to spots / dots = max 2

allow colouring for colour

• 3 colours in Cola

allow more colours in cola or fewer colours in fruit drink

• 2 colours in Fruit drink

• one of the colours is the same

• two of the colours in Cola are different

• one of the colours in Fruit drink is different

allow some of the colours in the drinks are different

• one of the colours in Cola is the most soluble

accept one of the colours in Cola has the highest Rf value

3

(c) different substances travel at different speeds or have different retention times

accept different attraction to solid

ignore properties of compounds

1

(d) (i) Is there caffeine in a certain brand of drink?

1

(ii) any two from:

• cannot be done by experiment

• based on opinion / lifestyle choice

• ethical, social or economic issue

accept caffeine has different effects on different people

2

[11]

Q48.

(a) O2 in correct space

1

correct balancing

accept multiples

1

(b) (i) rate increases

incorrect reference to energy = max 2

ignore references to equilibrium

1

because particles are closer together

accept because there are more particles (per unit volume)

allow particles have less space / room to move around

1

so frequency of collisions increases

accept particles are more likely to collide

ignore more collisions

ignore more successful collisions

1

(ii) has a greater surface area

1

so the reaction is faster

accept so more frequent collisions

1

(c) the (minimum) amount of energy (particles must have) to react or to start a reaction

accept the energy needed to break bonds

ignore references to heat

1

(d) (i) (potassium is) too / very reactive

ignore potassium is a Group 1 / alkali metal

1

so dangerous / violent reaction

accept hydrogen produced rapidly

1

(ii) ZnSO4

accept products in either order

ignore names of substances

1

H2

do not accept brackets or charges in the formulae

1

(iii) any one from:

• increase concentration (of sulfuric acid)

• increase temperature or heat it

• increase surface area of zinc

1

[13]

Q49.

(a) (i) so ions can move (and carry charge)

accept so current can flow

allow so it can conduct (electricity)

allow so charged particles can move

do not accept so electrons can move

1

(ii) because zinc ions gain electrons

accept because zinc ions are reduced

1

2 (electrons)

1

zinc is formed

accept correct half equation for 3 marks

if no mark gained allow

positive ions go to negative electrode or

opposites attract or

reduction (of zinc) or

(zinc) gains electrons for 1 mark

1

(iii) 2 Cl– Cl2 + 2 e–

must be completely correct

1

(b) (i) because the magnesium is a gas

allow magnesium goes from solid to gas

1

(ii) (a reaction which) takes in energy (from the surroundings)

accept more energy needed to break bonds than released by forming bonds

accept correct reference to energy level diagram

allow (a reaction which) takes in heat (from the surroundings)

1

(iii) (Mr MgO =) 40

accept (2 Mr MgO =) 80

1

1.2 / 24 (x40) or 0.05 (x40)

or

40 / 24 (x1.2) or 1.67 (x1.2)

allow ecf from step 1

1

2(.0)

allow ecf carried through from step 1

correct answer with or without working gains 3 marks

1

(iv) 75(%)

1

(v) any one from:

• the reaction is reversible

accept incomplete reaction

ignore equilibrium not reached

• some lost / escaped / released (when separated)

• some of the reactant may react in different ways from the expected reaction

• impure reactant(s)

ignore measurement and calculation errors

1

[12]

Q50.

(a) (i) burette

1

(ii) indicator

1

(iii) colour change

1

(b) (i) any one from:

• volume of (hydrochloric) acid

allow amount of (hydrochloric) acid

• concentration of (hydrochloric) acid

• concentration of (sodium) hydroxide

allow concentration of alkali

1

(ii) 22.3(0)

1

[5]

Q51.

(a) (i) Positive impact

any one from:

• provides employment or

• improves local economy

• improved transport - new roads are built, new rail links

• after use the quarry could provide recreation facilities

1

Negative impact

any one from:

• destruction of animal habitats

• fewer plants and trees to absorb carbon dioxide

• visual pollution or noise pollution or atmospheric / air pollution

allow dust pollution

• more traffic

• uses non-renewable resources

allow pollutants from burning diesel

1

(ii) economical

1

(b) carbon / coke burns (in oxygen / air)

accept carbon / coke reacts with oxygen / air

1

(c) (i) iron oxide (reactant)

must be words

1

carbon dioxide (product)

1

(ii) reduction

1

(d) (i) oxygen reacts with carbon

1

or

oxygen and carbon produce carbon dioxide / carbon monoxide

carbon dioxide / carbon monoxide is a gas

or

the carbon is removed as a gas

1

(ii) much harder

1

(e) Advantage:

less carbon dioxide is produced

1

Disadvantage:

there are different types of steel which must be sorted

1

[12]

Q52.

(a) four

1

covalent

1

(b) because it has a high melting point

accept it won’t melt

accept it won’t decompose or react

allow withstand high temperatures

ignore boiling point

1

(c) thin

1

[4]

Q53.

(a) (i) sulfuric

1

(ii) 1

1

(iii) to speed up the reaction

1

(b) because copper oxide in excess

allow copper oxide unreacted

or

because acid all used up / neutralised

1

(c) evaporation

allow heating

allow cooling

allow leave (to evaporate)

do not accept freezing

or

crystallisation

1

(d) Some copper sulfate may have been lost during the experiment

1

[6]

Q54.

(a) (i) because they are positively charged

accept they are positive / H+

accept oppositely charged or opposites attract

ignore they are attracted

1

(ii) gains one / an electron

accept H+ + e– → H or multiples

allow gains electrons

1

(b) 3 bonding pairs

1

1 lone pair

accept 2 non-bonding electrons on outer shell of nitrogen

1

(c) (i) hydroxide / OH–

do not accept sodium hydroxide

1

(ii) H+ + OH– → H2O

ignore state symbols

ignore word equation

1

(d) 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 Reference material.

0 marks

No relevant content.

Level 1 (1-2 marks)

There are basic descriptions of advantages or disadvantages of the electrolysis cells.

Level 2 (3-4 marks)

There are clear descriptions of environmental or economic advantages or disadvantages of the electrolysis cells. Comparisons may be implied.

Level 3 (5-6 marks)

There are detailed descriptions of environmental and economic advantages and disadvantages, comparing the electrolysis cells.

Examples of chemistry points made in the response:

Accept converse where appropriate.

• mercury cell is more expensive to construct

• mercury is recycled but membranes must be replaced

• mercury is toxic but membrane / polymer is not

• removing traces of mercury from waste is expensive

• mercury cell uses more electricity

• mercury cell produces chlorine that is purer

• mercury cell produces higher concentration / better quality of sodium hydroxide (solution)

6

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Q55.

(a) (i) to increase the rate of reaction

1

(ii) H2SO4 on the left hand side

1

H2O on right hand side

1

(iii) filtration

allow centrifuging or decanting

ignore evaporation if after filtration

1

(iv) crystallisation

ignore reference to filtration

unless given as an alternative

or

evaporation / heating / boiling / cooling

1

(v) any one from:

• because of an incomplete reaction

accept not all acid reacted

accept impure reactants

accept unexpected reaction

ignore reversible reaction

• because some (copper sulfate) lost on filtering or when poured into evaporating basin or boiled over or left in apparatus

must specify when lost

accept some (copper sulfate or acid) spilt

• weighing error (of copper sulfate)

1

(b) (i) reversible (reaction)

1

(ii) 300(J)

allow the same

1

(energy) given out / released

accept exothermic / –

ignore increasing or decreasing energy

1

(c)

1 mark for dividing mass by Ar (max 2 if Ar divided by mass)

1

= 0.06 = 0.02

1 mark for correct proportions

1

3 1

1 mark for correct whole number ratio (allow multiples). Can be awarded from formula

1

Cu3N

ecf allowed from step 2 to step 3 and step 3 to step 4 if sensible attempt at step 1

correct formula gains 1 mark

1

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