Distillation — final check key

1. DK1 · Final check

Model answer. Collected water is in the receiver after condensation. Some water and all nonvolatile salt remain in the flask as a more concentrated solution.

A full answer includes

• I placed condensed water in the receiver.
• I kept some water and all nonvolatile salt in the flask as more concentrated solution.

Watch for

• “Salt disappears during distillation.” — Salt stays in the remaining solution; water changes container and state.

2. DK2 · Final check

Model answer. Cooling water must enter the lower jacket inlet and leave the upper jacket outlet. The receiver collects sample that travels through the separate inner tube. Coolant must not mix with it.

A full answer includes

• I corrected coolant flow to the lower jacket inlet and upper outlet.
• I kept the receiver on the separate inner sample path.

Watch for

• “The jacket drains into the receiver.” — The jacket is a separate coolant circuit, surrounding the inner sample tube.

3. DK3 · Final check

Model answer. A boiling mixture can produce vapour containing both A and B. A is more volatile and enriches the early vapour; pure boiling points don’t make the components vaporise one at a time.

A full answer includes

• I explained that vapour above the boiling mixture can contain A and B together.
• I distinguished enrichment from components vaporising one at a time.

Also accept

• A boiling mixture can produce vapour containing both A and B. A is more volatile and enriches the early vapour; pure boiling points do not make the components vaporise one at a time.

Watch for

• “B waits until its pure boiling point before it can vaporise.” — Vapour from a mixture can contain both substances before that reading.

4. DK4 · Final check

Model answer. Keeping the early portion separate preserves its different composition. Residual vapour and liquid can still produce drops after heat is off; they must drain into the current receiver before exchange.

A full answer includes

• I kept the early fraction separate to preserve its composition.
• I drained residual vapour and liquid into the current receiver before exchanging it.

Watch for

• “Switching off heat stops every drop instantly.” — Stored heat and material in the apparatus can continue producing drops.

5. DK5 · Final check

Model answer. Filter out the insoluble grit. Fractionally distil the filtrate: repeated condensation and vaporisation in a column enrich the rising vapour in the more volatile liquid. Collect fractions separately. Both fractions can still contain both liquids.

A full answer includes

• I filtered grit and fractionally distilled the filtrate.
• I explained column enrichment and separate collection of fractions.
• I recognised that both fractions can still contain both liquids.

Watch for

• “A filter separates two miscible liquids.” — Both liquids pass through together. Their volatility difference requires distillation.

6. DK6 · Final check

Model answer. Use fractional distillation: the column repeatedly condenses and vaporises material, enriching rising vapour in the more volatile component. Fractions may still contain both liquids; boiling points and a column alone don’t prove purity.

A full answer includes

• I chose fractional distillation and explained repeated phase changes.
• I said enrichment and boiling-point data alone do not prove a pure product.

Also accept

• Use fractional distillation: the column repeatedly condenses and vaporises material, enriching rising vapour in the more volatile component. Fractions may still contain both liquids; boiling points and a column alone do not prove purity.

Watch for

• “A column guarantees any pair of liquids becomes pure.” — Mixture behaviour limits separation. Enriched fractions can contain both substances.