Answers · Distillation
Distillation — return questions key
Check meaning, not exact wording. These are teaching points, not official Cambridge marks.
1. DR1 · Return
Model answer. Water vaporises in the flask, condenses in the condenser inner tube and collects in the receiver. Coolant enters the lower jacket inlet and leaves the upper outlet. The bulb measures outgoing head-vapour temperature.
A full answer includes
- I explained vaporisation, condensation and collection in the receiver.
- I described low-to-high coolant flow and head-vapour thermometer placement.
Watch for
- “Evaporation alone collects the water.” — Evaporation into the room has no condenser or receiver to recover it.
2. DR2 · Return
Model answer. Repeated condensation and vaporisation enrich rising vapour in the more volatile component while less volatile material tends to return downwards.
A full answer includes
- I described repeated condensation and vaporisation enriching the rising vapour.
- I said less volatile material tends to return downwards while both liquids can enter vapour.
Watch for
- “Only A enters the column.” — Both liquids enter vapour. Repeated phase changes enrich, rather than perfectly exclude B.
3. DR3 · Return
Model answer. (a) Simple: volatile water can be recovered from nonvolatile salt by vaporisation and condensation. (b) Fractional: repeated phase changes in a column improve separation of the volatile liquids.
A full answer includes
- I chose simple distillation for volatile water and nonvolatile salt.
- I chose fractional distillation for improved separation of close-boiling miscible volatile liquids.
Watch for
- “Every clear mixture needs fractional distillation.” — Appearance doesn’t choose the method; use volatility and the product goal.