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Question 19M.3.sl.TZ1.c

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.3.sl.TZ1.c
Level sl Paper 3 Time zone TZ1
Command term Calculate Question number c Adapted from N/A
c.
[Maximum mark: 2]
19M.3.sl.TZ1.c

Starch is a natural polymer of glucose.

Calculate the energy released, in kJ g−1, when 3.49 g of starch are completely combusted in a calorimeter, increasing the temperature of 975 g of water from 21.0 °C to 36.0 °C. Use section 1 of the data booklet.

[2]

Markscheme

q = «mcΔT = 975 g × 4.18 J g–1 K–1 × 15.0 K =» 61 100 «J» / 61.1 «kJ»   [✔]

«heat per gram=  61.1  kJ 3 .49 g =» 17.5 «kJ g–1»  [✔]

 

Note: Award [2] for correct final answer.

Examiners report

Nearly half the students correctly calculated the enthalpy change and some of these went on to find the value in kJ g-1. The most common mistakes were to use the mass of starch rather than the mass of water and adding 273 to the temperature change.

Syllabus sections