Mark Scheme (Results) Summer 2018

Mark Scheme (Results)

Summer 2018

Pearson Edexcel International GCSE in

Chemistry (4CH0) Paper 1CR

Pearson Edexcel International in Science

Double Award (4SC0) Paper 1CR

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Summer 2018

Publications Code 4CH0_1CR_1806_MS

All the material in this publication is copyright

General Marking Guidance

 All candidates must receive the same treatment. Examiners must

mark the first candidate in exactly the same way as they mark the

last.

 Mark schemes should be applied positively. Candidates must be

rewarded for what they have shown they can do rather than

penalised for omissions.

 Examiners should mark according to the mark scheme not

according to their perception of where the grade boundaries may

lie.

 There is no ceiling on achievement. All marks on the mark scheme

should be used appropriately.

 All the marks on the mark scheme are designed to be awarded.

Examiners should always award full marks if deserved, i.e. if the

answer matches the mark scheme. Examiners should also be

prepared to award zero marks if the candidate’s response is not

worthy of credit according to the mark scheme.

 Where some judgement is required, mark schemes will provide the

principles by which marks will be awarded and exemplification may

be limited.

 When examiners are in doubt regarding the application of the mark

scheme to a candidate’s response, the team leader must be

consulted.

 Crossed out work should be marked UNLESS the candidate has

replaced it with an alternative response.

Question

number

Answer

Marks

1

Information

Substance

a good

conductor of

electricity

copper

a noble gas

helium

a mixture

air

a liquid at

room

temperature

bromine

used in fire

extinguishers

carbon

dioxide/helium/nitrogen

used as a

fuel

methane

6

Total for Question 1 = 6

Question

number

Answer

Notes

Marks

2

(a)

Any 3 from

M1 (moving) water particles/molecules

bombard/collide with the sugar cube

M2 sugar particles/molecules go into

solution/dissolve

M3 sugar particles/molecules spread

out/diffuse/move randomly

M4 (until) sugar particles/molecules are

distributed evenly in the water

ALLOW sugar particles

move from area of high

concentration to area of low

concentration

Max 2 if no reference to

sugar particles/ molecules

3

(b)

(i)

B distillation

A is incorrect as the diagram does not show the apparatus used for

crystallisation

C is incorrect as the diagram does not show the apparatus used for filtration

D is incorrect as the diagram does not show the apparatus used for sublimation

1

(ii)

P tripod

4

Q gauze

ACCEPT wire gauze

R condenser

ALLOW condensing tube

S conical flask

Do not allow just flask

Total for Question 2 = 8

Question

number

Answer

Notes

Marks

3

(a)

pencil/it won’t dissolve (in water/solvent)

ACCEPT ink/pen would/might

dissolve (in water/solvent)

ALLOW pencil won’t separate (in

the water)

1

ALLOW ink would mix with the food

colourings/water

ALLOW ink would

smudge/run/separate (in the

water)/interfere with the results

(b)

(i)

D contains only one colouring

A is incorrect as drink A contains three colourings

B is incorrect as drink B contains two colourings

C is incorrect as drink C contains three colourings

1

(ii)

M1 C

M2 spot moved the furthest/greatest

distance

ACCEPT has a spot nearest to

water/solvent front

ALLOW

blob/dot/mark/point/colour/dye for

spot

M2 dep on M1 correct or missing

2

Question

number

Answer

Notes

Marks

(iii)

M1 A and C

M2 have spot at same level/travelled

same distance

ALLOW spots align/have same R

f

values

ALLOW blob/dot/mark/point/colour

/dye for spot

M2 dep on M1

2

Total for Question 3 = 6

Question

number

Answer

Notes

Marks

4

(a)

proton 1 +1

neutron 1 0

electron 1/1836 -1

ALLOW zero / neutral / no charge /

none

ALLOW 1/1800 to 1/2000

3

ALLOW 0.0005 to 0.00056

ALLOW negligible

All 6 correct 3 marks

4 or 5 correct 2 marks

2 or 3 correct 1 mark

REJECT 0 / almost 0

Columns reversed MAX 1

(b)

(i)

T

ALLOW Mg / magnesium

1

(ii)

T

ALLOW Mg / magnesium

1

(iii)

Q

ALLOW O

2-

/ oxide ion

1

(iv)

S

ALLOW F / fluorine

1

(c)

D the same number of protons

A is incorrect as isotopes do not have a different atomic number

B is incorrect as isotopes do not have a different number of electrons

C is incorrect as isotopes do not have the same number of neutrons

1

Total for Question 4 = 8

Question

number

Answer

Notes

Marks

5

(a)

(i)

A atomic number

B is incorrect as the elements in the Periodic Table are not arranged in order of

increasing mass number

C is incorrect as the elements in the Periodic Table are not arranged in order of

increasing neutron number

D is incorrect as the elements in the Periodic Table are not arranged in order of

increasing relative atomic mass

1

(ii)

Phosphorus/P

1

(iii)

Any two from:

M1 carbon

M2 nitrogen

M3 fluorine

ALLOWC/N/F

ALLOW N

2

/F

2

ALLOW boron/B

ALLOW 1 mark for names/formulae of

two correct acidic oxides

2

Question

number

Answer

Notes

Marks

5

(a)

(iv)

M1 acid rain

ACCEPT makes lakes acidic / lowers pH of

lakes

IGNORE pollution

2

M2 specified problem for environment

caused by

acid rain

plants/trees/vegetation/crops/named

example dies/stunted

growth/harmed/damaged/poisoned

IGNORE deforestation/ leaching minerals

fish/aquatic animals/pond life/marine

life/named example dies/stunted

growth /harmed /damaged /poisoned

IGNORE references to just animals

limestone/marble reacts/corrodes/is

eaten away

NOT just buildings

IGNORE rusts or physical process such as

erosion /

weathering/ wearing away / dissolving

ACCEPT destroys for adverse effect in all of

above

IGNORE respiratory problems

IGNORE harmful/dangerous

Question

number

Answer

Notes

Marks

5

(b)

(i)

magnesium + sulfur  magnesium sulfide

ACCEPT sulphur

ACCEPT magnesium sulphide

1

REJECT magnesium sulfite /

magnesium sulfate

(ii)

M1 (each) magnesium/Mg (atom) loses

two electrons

/Mg (electronic configuration) changes

from 2.8.2 to 2.8

M2 (each) sulfur/S (atom) gains two

electrons

/S (electronic configuration) changes from

2.8.6 to 2.8.8

M3 Mg

2+

and S

2-

Mg transfers two electrons to S

scores M1 and M2

ALLOW 1 mark for Mg loses

electron(s) and S gains electron(s)

No M1 or M2 if mention of electron

sharing or covalent bonding

ALLOW Mg (ion) has a charge of

2+/+2 and S (ion) has a charge of 2-

/-2

Two correct ionic half equations

scores all 3 marks

3

Diagrams showing electron transfer

and charges on the ions scores all 3

marks

Question

number

Answer

Notes

Marks

5

(b)

(iii)

M1 n(Mg) = 0.30/24 = 0.0125

M2 M

r

(MgS) = 56

M3 mass MgS = 0.0125 x 56 = 0.7(0)g

OR

M1 Mr (MgS) = 56

M2 (so) 24 (g Mg) gives 56 (g MgS)

M3 (so) 0.30 (g Mg) gives 56/24 x 0.3 =

0.7(0) g

Correct answer with no working or

alternative correct working scores 3

marks

BUT if atomic numbers used in M1

and M2 only M3 can be scored (for

an answer of 0.7g)

ALLOW ECF if M1 and/or M2

incorrect

ALLOW ECF for M2 and M3 if M1

incorrect

3

Total for Question 5 = 13

Question

number

Answer

Notes

Marks

6

(a)

CaCO

3

+ 2HNO

3

 Ca(NO

3

)

2

+ CO

2

+ H

2

O

M1 all correct formulae

M2 correct balancing

M2 DEP on M1

ALLOW multiples

IGNORE state symbols even if

incorrect

2

(b)

(i)

M1 carbon dioxide/gas would escape

through

thistle funnel

M2 should collect by downward delivery

/gas jar

wrong way up OWTTE

ACCEPT end of thistle funnel

should go into the acid

ALLOW should be a tap on thistle

funnel

ACCEPT carbon dioxide/gas more

dense than air so would not go

into gas jar OWTTE

IGNORE should collect gas over

water / in a gas syringe

2

(ii)

M1 calcium sulfate insoluble

M2 (calcium sulfate) forms coating on

marble chips (and stops acid reacting with

marble chips) OWTTE

ALLOW calcium sulfate only

slightly soluble / is a precipitate

ALLOW solid calcium sulfate

produced

2

Question

number

Answer

Notes

Marks

(c)

C weakly acidic

A is incorrect because a solution with pH 6 is not weakly alkaline

B is incorrect because a solution with pH 6 is not strongly alkaline

C is incorrect because a solution with pH 6 is not strongly acidic

1

Question

number

Answer

Notes

Marks

6

(d)

(i)

M1 (electrostatic) attraction between

bonding/shared pair(s) of electrons

M2 and nuclei (of both atoms)

OR

M1 bonding/shared pair(s) of electrons

M2 attracted to nuclei (of both atoms)

ALLOW electrostatic forces for

attraction

Do not award M2 if reference to

only one nucleus

Do not award M2 if reference to

only one nucleus

2

If the implication is that the

shared pair of electrons is between

molecules or ions rather than

atoms scores 0 out of 2

(ii)

M1 weak forces/attraction(s) between

molecules

/ weak intermolecular forces

M2 (so) little (thermal/heat) energy

required to overcome the forces

/attraction(s) (between molecules)

/separate the molecules

ALLOW weak bonds between

molecules / intermolecular bonds

ALLOW little energy needed to

break the bonds if it is clear that

they are referring to

intermolecular forces

IGNORE less energy required

Any reference to weak covalent

bonds / weak bonds between

atoms or breaking of covalent

bonds /breaking of bonds between

atoms scores 0 out of 2

2

Question

number

Answer

Notes

Marks

6

(d)

(iii)

M1 two pairs electrons between carbon

atom and

both oxygen atoms

ALLOW any combination of dots

and crosses

2

M2 rest of molecule fully correct

M2 DEP on M1

Total for Question 6 = 13

Question

number

Answer

Notes

Marks

7

(a)

haematite

1

(b)

nitrogen

ACCEPT N

2

REJECT other gases

1

(c)

M1 carbon reacts with oxygen to form

carbon

dioxide

M2 carbon dioxide reacts with carbon to

form

carbon monoxide

ACCEPT word or chemical equations

for both marks

ALLOW coke for carbon in M1 and

M2

ALLOW carbon dioxide is formed by

the decomposition of

limestone/word or chemical

equation to show this

ALLOW (carbon monoxide is formed

by) incomplete combustion of

carbon/coke or chemical equation to

show this for 1 mark

2

Carbon reacts with oxygen alone is

insufficient

Question

number

Answer

Notes

Marks

7

(d)

Fe

2

O

3

+ 3CO  2Fe + 3CO

2

ACCEPT multiples and fractions

2

M1 correct formulae

M2 correct balancing

M2 dependent on M1

Total for Question 7 = 13

Question

number

Answer

Notes

Marks

8

(a)

(i)

thermometer

ALLOW Bunsen (burner)

1

(ii)

M1 to cool the vapour(s)/gas(es)

M2 (and) to condense it/turn it to liquid

2

(b)

(i)

(Fraction) A

ALLOW (boiling point) 30-60

1

(ii)

(Fraction) A

ALLOW (boiling point) 30-60

1

(c)

(i)

C

10

H

22

Penalise incorrect use of

case/superscripts etc

1

(ii)

C

n

H

2n+2

1

Question

number

Answer

Notes

Marks

8

(d)

(i)

C

14

H

30

 C

8

H

18

+

2 C

3

H

6

ALLOW C

3

H

6

+ C

3

H

6

M1 C

3

H

6

M2 fully correct equation

ALLOW 1 mark for C

2

H

4

+ C

4

H

8

or

C

6

H

12

in fully correct equation

2

(ii)

M1 silica / alumina

M2 600-700 (ºC)

ACCEPT aluminium oxide/silicon

dioxide /Al

2

O

3

/SiO

2

/

aluminosilicate(s)/zeolite(s)

ACCEPT any temperature in the

range 600 to 700 inclusive

2

Total for Question 8 = 11

Question

number

Answer

Notes

Marks

9

(a)

(i)

no change/no reaction OWTTE

1

(ii)

most sodium

magnesium

zinc

least platinum

ACCEPT correct symbols

1

(iii)

(when mixed with air) burns with pop

Must be reference to test and result

ACCEPT lighted spill/splint and pop

1

REJECT glowing spill/splint

IGNORE squeaky pop test alone

(iv)

magnesium + hydrochloric acid 

magnesium chloride + hydrogen

ACCEPT correct chemical equation

1

(v)

explodes/violent (reaction)

ALLOW dangerous/unsafe

ALLOW sodium too reactive/very

reactive/reaction too vigorous

1

Question

number

Answer

Notes

Marks

9

(b)

(i)

Any 2 from

M1 brown/pink/pink-brown solid formed

M2 (blue) solution turns colourless/is decolourised /

colour of solution fades/turns paler (blue)

ACCEPT brown/pink/pink-brown

coating on zinc

ALLOW brown/pink/pink-brown

precipitate

ALLOW red-brown

REJECT incorrect initial colour of

solution

2

M3 zinc metal gets smaller

ALLOW zinc dissolves/disappears

IGNORE bubbles/effervescence

(ii)

M1 don’t know whether zinc or nickel is more

reactive

2

M2 because no experiment was done between a

zinc salt and nickel/ a nickel salt and zinc OWTTE

ALLOW no experiment was done to

compare zinc and nickel/need to do

experiment to compare zinc and

nickel OWTTE

Question

number

Answer

Notes

Marks

9

(c)

M1 zinc/Zn loses electrons

M2 copper ion/Cu

2+

gains electrons

M3 zinc/Zn is oxidised and copper/Cu (ion)/Cu

2+

is

reduced

ALLOW correct explanations in

terms of oxidation number changes

ACCEPT correct half equations for

M1 and M2

ALLOW both oxidation and reduction

occur (at same time/in same

reaction)

IGNORE references to loss and gain

of oxygen

3

Total for Question 9 = 12

Question

number

Answer

Notes

Marks

10

(a)

(i)

M1 in nitrogen/in an element all atoms

contain the same number of protons/have

the same atomic number

M2 ammonia contains two elements/two

different types of atoms/N and H

(chemically) bonded together/chemically

combined

ALLOW nitrogen / an element contains

only one type of atom

ALLOW nitrogen only contains nitrogen

atoms

ACCEPT contains atoms with different

numbers of protons/different atomic

numbers

2

(ii)

M1 (X) hydrogen

M2 (raw material) natural gas

ALLOW H

2

IGNORE H

ALLOW

methane/hydrocarbons/water/steam

2

(iii)

Iron/Fe

1

(iv)

catalyst

ACCEPT references to speed up

reaction

IGNORE lowers activation energy

1

Question

number

Answer

Notes

Marks

10

(b)

(i)

neutralisation

ACCEPT acid-base

IGNORE exothermic

1

(ii)

M1 ammonium sulfate

M2 (NH

4

)

2

SO

4

REJECT ammonium sulfite/sulfide

2

(iii)

M1 add (aqueous) sodium

hydroxide/NaOH

M2 test gas/ammonia with (moist/damp)

red litmus

M3 (litmus) turns blue

If incorrect or no reagent 0 marks

ALLOW other alkalis

ACCEPT pH/UI paper

ACCEPT indigo/violet/purple if pH

paper used

3

If implication that they are testing the

solution with litmus no M2 or M3

Question

number

Answer

Notes

Marks

10

(c)

M1 liquid occupies smaller volume

OWTTE

M2 so can transport larger mass/amount

(in same size container)

OR

M1 gas transported under pressure

ACCEPT particles in liquid closer together

ORA

ACCEPT liquid more dense than gas

2

M2 risk of explosion / leakage

(d)

(i)

enthalpy change

ACCEPT heat (energy) change/thermal

energy change

IGNORE energy change

IGNORE enthalpy alone

1

(ii)

(forward) reaction exothermic

ACCEPT backward reaction is

endothermic

1

(iii)

more moles (of gas) on right hand

side/product side ORA

ACCEPT 9 moles on LHS and 10 moles on

RHS

ALLOW molecules/particles for moles

1

Question

number

Answer

Notes

Marks

10

(e)

M1 it is a fertiliser/ it contains nitrogen

M2 and therefore increases crop yield /

provides essential nutrients for plant

growth

ALLOW it provides nitrate ions

ALLOW helps crops/plants grow

faster/increases plant growth

ALLOW for plants to make amino

acids/proteins

2

Total for Question 10 = 19

Question

number

Answer

Notes

Marks

11

(a)

(i)

Pb(NO

3

)

2

(aq) + K

2

CrO

4

(aq)  PbCrO

4

(s)

+ 2KNO

3

(aq)

1

(ii)

2‒/CrO

4

2-

ACCEPT ‒2/CrO

4

-2

1

(b)

(i)

M1& M2 all eleven points plotted to

nearest gridline

Deduct 1 mark for each error

2

(ii)

anomalous point (at 2.1, 14) circled

1

(iii)

M1 best fit straight line through first 6

points drawn

with aid of a ruler

2

M2 best fit straight line through last 5 points

drawn

with aid of a ruler

No penalty if lines do not cross or if the

two straight lines are joined by a curve

Penalise lack of use of a ruler once only

Question

number

Answer

Notes

Marks

11

(b)

(iv)

volume from candidate’s graph to ± 0.2 cm

3

Do not award mark if lines do not cross.

1

(v)

Any 2 from

M1 started with less than 5cm

3

potassium

chromate

M2 added too little lead(II) nitrate

M3 precipitate not left for long enough to

settle

If no other mark scored allow 1 mark for

misread volume/misread height

2

(c)

(i)

M1 filter (off the precipitate)

M2 wash precipitate/solid/lead(II) chromate

(with

distilled/deionised/pure water)

M3 dry in a (warm) oven / leave to dry / dry

with filter

paper

ALLOW ‘decant’

REJECT refs to crystallisation for M2 and

M3

REJECT any direct method of heating

with a flame, eg Bunsen burner

3

(ii)

M1 flame test

M2 lilac

ACCEPT description of flame test

IGNORE burn

ALLOW purple/pink

2

Question

number

Answer

Notes

Marks

11

(d)

M1 n[KI] = 5.0 x 0.90/1000 = 0.0045 (mol)

M2 n[(Pb(NO

3

)

2

] = ½ x M1 = 0.00225 (mol)

M3 conc

n

[Pb(NO

3

)

2

] = M2 x1000/8 = 0.28

(mol/dm

3

)

Correct answer without working scores

3 marks

ACCEPT any number of sig figs, correctly

rounded, except 1

Calculator value is 0.28125

3

0.56(25) and 1.1(25) both score 2

marks

Total for Question 11 = 18

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