DP Chemistry (last assessment 2024)
Question 20N.2.hl.TZ0.5f(ii)
| Date | November 2020 | Marks available | [Maximum mark: 2] | Reference code | 20N.2.hl.TZ0.5f(ii) |
| Level | hl | Paper | 2 | Time zone | TZ0 |
| Command term | Justify, Predict | Question number | f(ii) | Adapted from | N/A |
f(ii).
[Maximum mark: 2]
20N.2.hl.TZ0.5f(ii)
A student performs a titration to determine the concentration of ethanoic acid, , in vinegar using potassium hydroxide.
(f(ii))
Potassium hydroxide solutions can react with carbon dioxide from the air. The solution was made one day prior to using it in the titration.
Predict, giving a reason, the effect of this error on the calculated concentration of ethanoic acid in 5(e).
[2]
Markscheme
would be higher ✔
actual is lower «than the value in calculation»
OR
larger volume of «solution» needed to neutralize the acid ✔
Accept partially neutralised by from air.
Examiners report
Most candidates identified that the systematic error would result in the concentration of the alkali being lowered but then failed to propagate this through to the effect on the concentration of the acid.
