AqA EXAMPRO
A-LEVEL CHEMISTRY MARK SCHEME
Practice Paper 3 Maximum marks: 90
View detailed guidance on the conclusions you can draw from your students' performance in
these papers on the MERiT welcome page. Understand how your students compare with
others and target revision effectively by entering marks into MERiT.
1. (a) Start a clock when KCl is added to water 1
Record the temperature every subsequent minute for about 5 minutes 1
Allow record the temperature at regular time intervals until
some time after all the solid has dissolved for M2
Plot a graph of temperature vs time 1
Extrapolate back to time of mixing = 0 and determine the temperature 1
Drawing of suitable graph could score M2, 3 and 4
(b) Heat taken in = m × c × ΔT = 50 × 4.18 × 5.4 = 1128.6 J 1
Max 2 if 14.6 °C used as ΔT
Moles of KCl = 5..6 = 0.0670 1
Enthalpy change per mole = +1128..0670 = 16 839 J mol-1 1
= +16.8 (kJ mol-1) 1
Answer must be given to this precision
(c) ΔHsolution = 1
ΔHlattice + ΔH(hydration of calcium ions) + 2 × ΔH(hydration of chloride ions)
ΔHlattice = ΔHsolution – ΔH(hydration of calcium ions) –2 ×ΔH(hydration of chloride ions)
ΔHlattice = –82–9 – (–1650 + 2 × –364) = +2295 (kJ mol–1) 1
(d) Magnesium ion is smaller than the calcium ion 1
Therefore, it attracts the chloride ion more strongly / stronger ionic bonding 1
[Total 12 marks]
2 (a) (i) Correctly plots all points (± one square) and draws straight line of best fit 1
Lose this mark if the candidate’s line is doubled or kinked.
Lose this mark if the line does not pass within one square of the
origin, extending the line if necessary.
Plotted points cover over half of grid 1
(ii) 0.046 ± 0.002 (mol dm−3) 1
0.088 to 0.096 (mol dm−3) 1
Allow M1 × 2
Allow two marks for correct answer.
Answer must be to at least two significant figures.
Page 1
, (iii) Total volume = (100 × 0.1) / 0.04 = 250 (cm3) 1
Allow any correct alternative method of working.
Therefore add 150 cm3 1
Correct answer without working scores M2 only.
(b) Iron needed for haemoglobin / for red blood cells / 1
to carry oxygen around the body
Accept well-water may contain eg Ca2+ ions / dissolved
minerals that are good for bones / teeth etc.
[Total 7 marks]
3 (a) Electron pair donor 1
OR Species which uses a pair of electrons to form a co-ordinate / covalent bond.
QoL
Credit “lone pair” as alternative wording
(b)
M1 Must show an arrow from the lone pair of electrons on the carbon atom 1
of the negatively charged cyanide ion to the central C atom.
M2 Must show the movement of a pair of electrons from 1
the C-Br bond to the Br atom. Mark M2 independently.
Award full marks for an SN1 mechanism in which M1 is the attack of the
cyanide ion on the intermediate carbocation.
Penalise M1 if covalent KCN is used
Penalise M2 for formal charge on C or incorrect partial charges
Penalise once only for a line and two dots to show a bond.
Max 1 mark for the wrong reactant or “sticks”
(c) Ethylamine / CH3CH2NH2 is a nucleophile 1
OR Ethylamine could react further
OR Ethylamine could make secondary / tertiary amines
OR To make reaction with ammonia more likely
OR To minimise further substitution
OR The idea of releasing free amine from the salt
OR The idea of removing a proton from the intermediate alkylammonium ion
OR The idea that ammonia acts both initially as a nucleophile and then as a base
Do not credit a simple reference to the equation or the
mechanism requiring two moles of ammonia.
(d) 4
Name of organic product: ethylpropanoate (1)
[Total 8 marks]
A-LEVEL CHEMISTRY MARK SCHEME
Practice Paper 3 Maximum marks: 90
View detailed guidance on the conclusions you can draw from your students' performance in
these papers on the MERiT welcome page. Understand how your students compare with
others and target revision effectively by entering marks into MERiT.
1. (a) Start a clock when KCl is added to water 1
Record the temperature every subsequent minute for about 5 minutes 1
Allow record the temperature at regular time intervals until
some time after all the solid has dissolved for M2
Plot a graph of temperature vs time 1
Extrapolate back to time of mixing = 0 and determine the temperature 1
Drawing of suitable graph could score M2, 3 and 4
(b) Heat taken in = m × c × ΔT = 50 × 4.18 × 5.4 = 1128.6 J 1
Max 2 if 14.6 °C used as ΔT
Moles of KCl = 5..6 = 0.0670 1
Enthalpy change per mole = +1128..0670 = 16 839 J mol-1 1
= +16.8 (kJ mol-1) 1
Answer must be given to this precision
(c) ΔHsolution = 1
ΔHlattice + ΔH(hydration of calcium ions) + 2 × ΔH(hydration of chloride ions)
ΔHlattice = ΔHsolution – ΔH(hydration of calcium ions) –2 ×ΔH(hydration of chloride ions)
ΔHlattice = –82–9 – (–1650 + 2 × –364) = +2295 (kJ mol–1) 1
(d) Magnesium ion is smaller than the calcium ion 1
Therefore, it attracts the chloride ion more strongly / stronger ionic bonding 1
[Total 12 marks]
2 (a) (i) Correctly plots all points (± one square) and draws straight line of best fit 1
Lose this mark if the candidate’s line is doubled or kinked.
Lose this mark if the line does not pass within one square of the
origin, extending the line if necessary.
Plotted points cover over half of grid 1
(ii) 0.046 ± 0.002 (mol dm−3) 1
0.088 to 0.096 (mol dm−3) 1
Allow M1 × 2
Allow two marks for correct answer.
Answer must be to at least two significant figures.
Page 1
, (iii) Total volume = (100 × 0.1) / 0.04 = 250 (cm3) 1
Allow any correct alternative method of working.
Therefore add 150 cm3 1
Correct answer without working scores M2 only.
(b) Iron needed for haemoglobin / for red blood cells / 1
to carry oxygen around the body
Accept well-water may contain eg Ca2+ ions / dissolved
minerals that are good for bones / teeth etc.
[Total 7 marks]
3 (a) Electron pair donor 1
OR Species which uses a pair of electrons to form a co-ordinate / covalent bond.
QoL
Credit “lone pair” as alternative wording
(b)
M1 Must show an arrow from the lone pair of electrons on the carbon atom 1
of the negatively charged cyanide ion to the central C atom.
M2 Must show the movement of a pair of electrons from 1
the C-Br bond to the Br atom. Mark M2 independently.
Award full marks for an SN1 mechanism in which M1 is the attack of the
cyanide ion on the intermediate carbocation.
Penalise M1 if covalent KCN is used
Penalise M2 for formal charge on C or incorrect partial charges
Penalise once only for a line and two dots to show a bond.
Max 1 mark for the wrong reactant or “sticks”
(c) Ethylamine / CH3CH2NH2 is a nucleophile 1
OR Ethylamine could react further
OR Ethylamine could make secondary / tertiary amines
OR To make reaction with ammonia more likely
OR To minimise further substitution
OR The idea of releasing free amine from the salt
OR The idea of removing a proton from the intermediate alkylammonium ion
OR The idea that ammonia acts both initially as a nucleophile and then as a base
Do not credit a simple reference to the equation or the
mechanism requiring two moles of ammonia.
(d) 4
Name of organic product: ethylpropanoate (1)
[Total 8 marks]
