Q9.
A
[1]
Q10.
(a)
M1
Correct answer scores 4 marks
1
M2 heat released = 1216 x 1000 x 0.0075 (= 9120) (J)
[or 1216 x 0.0075 = (9.12) (kJ)]
0.0075 scores M1 with or without working
9120 or 9.12 scores M1 and M2 with or without working
1
M3
Allow ECF at each stage
correct M3 scores M1 and M2
1
M4 final temperature = 19.1 + M3 = 62.7 or 63 (°C)
1
Alternative M3/4
M3 9120 = 50 × 4.18 × (Final T – 19.1)
M4 Final T = 62.7 or 63 (°C)
Ignore negative sign for q in M2 and/or ΔT in M3, but penalise if used as a temperature fall in M4 (if alternative method used for M3/4 and negative value for q is used, allow M3 for expression with negative q value but do not allow M4)
(temperatures to at least 2sf)
If candidates use a value in kJ rather than J to find ΔT / final T then they lose M3, but ECF to M4 [e.g. 9.12 rather than 9120 giving ΔT = 0.0436 and final temperature = 19.1(436) – this would give 3 marks]
If candidates use 0.63 g for m in M3, they will get ΔT = 3.46 and final temperature = 22.56 – this would give 3 marks]
Cannot score M2 using moles = 1
(b) thermal energy / heat loss or
or idea of heat being transferred to calorimeter
incomplete combustion or
allow idea that it is not under standard conditions
evaporation
allow no lid / poor/no insulation
1
(c) M1 6 × (–394), 6 × (–286) and –3920
1
M2 (ΔH =) [6 × (–394)] + [6 × (–286)] + 3920
(or (ΔH =) [–2364)] + [–1716)] + 3920)
(or (ΔH =) –4080 + 3920)
1
M3 = –160 (kJ mol–1)
1
–160 scores 3 marks; +160 scores 2 marks
–8000 scores 2 marks; +8000 scores 1 mark
–1876 scores 2 marks; +1876 scores 1 mark
M1 is for correct coefficients, i.e. 6 × ΔcH H2 & 6 × ΔcH C & 1 x ΔcH C6H12 (ignore whether + or –)
ECF from M1 to M2/3 for incorrect coefficients / arithmetic error / transposition
ECF from M2 to M3 for use of products – reactants
Ignore any cycle
[8]