DP Chemistry (last assessment 2024)
Question 19N.2.hl.TZ0.b(ii)
| Date | November 2019 | Marks available | [Maximum mark: 2] | Reference code | 19N.2.hl.TZ0.b(ii) |
| Level | hl | Paper | 2 | Time zone | TZ0 |
| Command term | Apply, Describe | Question number | b(ii) | Adapted from | N/A |
b(ii).
[Maximum mark: 2]
19N.2.hl.TZ0.b(ii)
Another common acid found in food is ethanoic acid.
Describe, using a suitable equation, how the buffer solution formed during the titration resists pH changes when a small amount of acid is added.
[2]
Markscheme
ALTERNATIVE 1:
H+ (aq) + CH3COO– (aq) → CH3COOH (aq) ✔
added acid neutralised by ethanoate ions
OR
«weak» CH3COOH (aq)/ethanoic acid replaces H+ (aq)
OR
CH3COOH/CH3COO– ratio virtually/mostly unchanged ✔
ALTERNATIVE 2:
CH3COOH (aq) H+ (aq) + CH3COO– (aq) ✔
equilibrium shifts to the ethanoic acid side
OR
CH3COOH/CH3COO− ratio virtually/mostly unchanged ✔
