Question 19N.2.hl.TZ0.b
| Date | November 2019 | Marks available | [Maximum mark: 2] | Reference code | 19N.2.hl.TZ0.b |
| Level | hl | Paper | 2 | Time zone | TZ0 |
| Command term | Outline, State | Question number | b | Adapted from | N/A |
A molecule of citric acid, C6H8O7, is shown.
The equation for the first dissociation of citric acid in water is
C6H8O7 (aq) + H2O (l) C6H7O7− (aq) + H3O+ (aq)
Outline two laboratory methods of distinguishing between solutions of citric acid and hydrochloric acid of equal concentration, stating the expected observations.
[2]
Any two of:
«electrical» conductivity AND HCl greater ✔
pH AND citric acid higher ✔
titrate with strong base AND pH at equivalence higher for citric acid ✔
add reactive metal/carbonate/hydrogen carbonate AND stronger effervescence/faster reaction with HCl ✔
titration AND volume of alkali for complete neutralisation greater for citric acid ✔
titrate with strong base AND more than one equivalence point for complete neutralisation of citric acid ✔
titrate with strong base AND buffer zone with citric acid ✔
NOTE: Accept “add universal indicator AND HCl more red/pink” for M2.
Accept any acid reaction AND HCl greater rise in temperature.
Accept specific examples throughout.
Do not accept “smell” or “taste”.
