AQA A-LEVEL CHEMISTRY 7405/3 Paper 3 JUNE 2025 Combined Question
Paper and Mark Scheme
A-level
CHEMISTRY
7405/3
Paper 3
Mark scheme
June 2025
Version: 1.0 Final
, MARK SCHEME – A-LEVEL CHEMISTRY – 7405/3 – JUNE 2025
Question Answers Additional comments/Guidelines Mark
KOH(s) → K+(aq) + OH–(aq) ALLOW (+)aq on arrow
OR ALLOW KOH(aq) as product 1
01.1 KOH(s) + aq → K+(aq) + OH–(aq) IGNORE H2O on arrow
State symbols are essential NOT equations with H2O on the LHS and/or RHS (1 x AO1)
NOT ⇌
Question Answers Additional comments/Guidelines Mark
M1 Amount of KOH = 3.00 (= 0.053475935 mol)
56.1
M2 q = ΔH × 0.0535 ( = 2.74455 kJ) = 2745 J
M2 q = ΔH x M1
For M2, M1 must be an attempt at calculating
amount of KOH
M3 ΔT = 30.4 – 18.1 (= 12.3 °C)
M4/M5 ALLOW actual answers OR actual
𝑞 M2 in J answers minus 3 if mass KOH subtracted
M4 m (= ) = = 49.8 – 50.4 g
c∆T 4.18 × M3
M4 ALLOW m (= 𝑞 ) = M2 in kJ 5
c∆T 4180 × M3
3
01.2 M4 ALLOW if M2 left in kJ if M5 in dm (4 x AO2,
1 x AO3)
52.8 – 53.4 cm3 = 5 marks
Answer must be to min 2 sig. fig. and units of
cm3
M5 = answer to M4 in cm3 ALLOW units of dm3 only if answer given as
0.0528 - 0.0534 dm3 to min 2 sf
M5 2.30 cm3 from ΔT = 12.3 + 273 (NOT M3)
M5 0.998 cm3 comes from 51..18 x 12.3 = M3 &
M5 (NOT M2 & M4). Look for M1 separately
M5 998 cm3 comes from .18 x 12.3 = M3,
M4 & M5 (NOT M2). Look for M1 separately
11
, MARK SCHEME – A-LEVEL CHEMISTRY – 7405/3 – JUNE 2025
Question Answers Additional comments/Guidelines Mark
M1 Enthalpy of solution = enthalpy of hydration K+ + enthalpy of OR cycle KOH(s) → K+(aq) + OH–(aq)
hydration OH– – Lattice enthalpy of formation
–789 –322 528
OR
= –322 – 528 – (–789) K+(g) + OH–(g)
OR
2
01.3 –789 + x = –322 + (–528)
–61 = 2 marks (2 x AO2)
–1
M2 –61 (kJ mol ) +61 = 1 mark
–1639 = 1 mark
NOT +1639 (0 marks)
Question Answers Additional comments/Guidelines Mark
ALLOW incomplete dissociation/reaction
ALLOW solution made in experiment is not to
infinite dilution
ALLOW thermal energy for ‘heat’
IGNORE not standard conditions / covalent
character / evaporation of water / apparatus
uncertainty 1
01.4 Heat losses OR incomplete dissolving IGNORE energy loss unqualified (1 x AO3)
IGNORE human error
IGNORE incomplete hydration
NOT data book values are averages
NOT incomplete combustion
NOT heat gain
NOT references to yield
12
Paper and Mark Scheme
A-level
CHEMISTRY
7405/3
Paper 3
Mark scheme
June 2025
Version: 1.0 Final
, MARK SCHEME – A-LEVEL CHEMISTRY – 7405/3 – JUNE 2025
Question Answers Additional comments/Guidelines Mark
KOH(s) → K+(aq) + OH–(aq) ALLOW (+)aq on arrow
OR ALLOW KOH(aq) as product 1
01.1 KOH(s) + aq → K+(aq) + OH–(aq) IGNORE H2O on arrow
State symbols are essential NOT equations with H2O on the LHS and/or RHS (1 x AO1)
NOT ⇌
Question Answers Additional comments/Guidelines Mark
M1 Amount of KOH = 3.00 (= 0.053475935 mol)
56.1
M2 q = ΔH × 0.0535 ( = 2.74455 kJ) = 2745 J
M2 q = ΔH x M1
For M2, M1 must be an attempt at calculating
amount of KOH
M3 ΔT = 30.4 – 18.1 (= 12.3 °C)
M4/M5 ALLOW actual answers OR actual
𝑞 M2 in J answers minus 3 if mass KOH subtracted
M4 m (= ) = = 49.8 – 50.4 g
c∆T 4.18 × M3
M4 ALLOW m (= 𝑞 ) = M2 in kJ 5
c∆T 4180 × M3
3
01.2 M4 ALLOW if M2 left in kJ if M5 in dm (4 x AO2,
1 x AO3)
52.8 – 53.4 cm3 = 5 marks
Answer must be to min 2 sig. fig. and units of
cm3
M5 = answer to M4 in cm3 ALLOW units of dm3 only if answer given as
0.0528 - 0.0534 dm3 to min 2 sf
M5 2.30 cm3 from ΔT = 12.3 + 273 (NOT M3)
M5 0.998 cm3 comes from 51..18 x 12.3 = M3 &
M5 (NOT M2 & M4). Look for M1 separately
M5 998 cm3 comes from .18 x 12.3 = M3,
M4 & M5 (NOT M2). Look for M1 separately
11
, MARK SCHEME – A-LEVEL CHEMISTRY – 7405/3 – JUNE 2025
Question Answers Additional comments/Guidelines Mark
M1 Enthalpy of solution = enthalpy of hydration K+ + enthalpy of OR cycle KOH(s) → K+(aq) + OH–(aq)
hydration OH– – Lattice enthalpy of formation
–789 –322 528
OR
= –322 – 528 – (–789) K+(g) + OH–(g)
OR
2
01.3 –789 + x = –322 + (–528)
–61 = 2 marks (2 x AO2)
–1
M2 –61 (kJ mol ) +61 = 1 mark
–1639 = 1 mark
NOT +1639 (0 marks)
Question Answers Additional comments/Guidelines Mark
ALLOW incomplete dissociation/reaction
ALLOW solution made in experiment is not to
infinite dilution
ALLOW thermal energy for ‘heat’
IGNORE not standard conditions / covalent
character / evaporation of water / apparatus
uncertainty 1
01.4 Heat losses OR incomplete dissolving IGNORE energy loss unqualified (1 x AO3)
IGNORE human error
IGNORE incomplete hydration
NOT data book values are averages
NOT incomplete combustion
NOT heat gain
NOT references to yield
12
