DP Chemistry (last assessment 2024)
Question 19M.3.sl.TZ1.7c
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.sl.TZ1.7c |
| Level | sl | Paper | 3 | Time zone | TZ1 |
| Command term | Calculate | Question number | c | Adapted from | N/A |
c.
[Maximum mark: 2]
19M.3.sl.TZ1.7c
Starch is a natural polymer of glucose.
(c)
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= =» 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.
