DP Chemistry (first assessment 2025)
Question 19M.2.SL.TZ1.d
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.SL.TZ1.d |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Calculate | Question number | d | Adapted from | N/A |
d.
[Maximum mark: 2]
19M.2.SL.TZ1.d
Sodium percarbonate, 2Na2CO3•3H2O2, is an adduct of sodium carbonate and hydrogen peroxide and is used as a cleaning agent.
Mr (2Na2CO3•3H2O2) = 314.04
Calculate the percentage by mass of hydrogen peroxide in sodium percarbonate, giving your answer to two decimal places.
[2]
Markscheme
M (H2O2) «= 2 × 1.01 + 2 × 16.00» = 34.02 «g» [✔]
«% H2O2 = 3 × × 100 =» 32.50 «%» [✔]
Note: Award [2] for correct final answer.
Examiners report
Calculating the % by mass was generally well answered although some candidates started by using rounded values of atomic masses which made their final answer unprecise.
Syllabus sections
Structure 1. Models of the particulate nature of matter » Structure 1.4—Counting particles by mass: The mole » Structure 1.4.5—The molar concentration is determined by the amount of solute and the volume of solution. Solve problems involving the molar concentration, amount of solute and volume of solution.