Question 19M.3.hl.TZ1.8c
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.hl.TZ1.8c |
| Level | hl | Paper | 3 | Time zone | TZ1 |
| Command term | Calculate | Question number | c | Adapted from | N/A |
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]
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.
The incorrect mass was frequently used when calculating energy released from combustion of starch in a calorimeter. Those who used the mass of water correctly frequently stopped when energy in kJ or J was calculated, and did not seem to notice that the question asked for the energy to be calculated in kJg−1 so a further calculation was required.
