(a) M1 moles ( = 
× 2.0) = 0.050
1
M2 heat released = 0.050 × 56.1 (= 2.805 kJ or 2805 J)
1
M3 ∆T = 
1
M4 ∆T = 
or 
= 13(.4) (°C)
Correct answer (to at least 2 sig fig) scores 4 marks
27 or 26.8°C (from moles of two reagents being added together for M2, or use of 25 cm3 in M4) scores 3 marks
0.013(.4)°C (from not converting kJ to J) scores 3 marks (loses M4) [0.027 or 0.0268°C would score 2 marks (loses M2 and M4)
M1 moles can be shown for either substance or without specifying the substance; if it is shown for both substances, must be correct for both for M1
Allow ECF from M1 to M2
Allow ECF from M2 to M4 (providing an attempt to calculate q has been made – no ECF if 56100 or 56.1 is used as q)
Correct M4 scores M3. If error made in M4, M3 could score from substituted values in this expression in M4
M4 final answer to at least 2 sig fig.
Penalise M4 for negative temperature rise
1
(b) M1 draws suitable best fit curve to 4 minutes
M1 line must be a curve and ignore value at 5 minutes
M1 line should not go to times before 4 minutes
1
M2 (17.2 – value read from graph line at 4 minutes) ± 0.2 (°C)
M2 allow use of any curved or straight line that is an attempt to draw a line through the values after 4 minutes (that may include the point at 5 minutes)
M2 allow negative values
1
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