DP Chemistry (last assessment 2024)

Test builder »

Question 19M.2.sl.TZ1.4d

Select a Test
Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.sl.TZ1.4d
Level sl Paper 2 Time zone TZ1
Command term Calculate Question number d Adapted from N/A
d.
[Maximum mark: 2]
19M.2.sl.TZ1.4d

This question is about peroxides.

(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 ×  34.02 314.04 × 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