Lesson overview
Distillation: Can we get the water back?
Get the water back from salty water: connect the condenser, predict what collects and read the thermometer. Then separate two liquids that mix with a fractionating column, and decide what to do when the reading rises.
Suggested sequence
- Lesson 1 · Can we get the water back? Recover the solvent. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 2 · What if both liquids can escape? Compare changing fractions. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 3 · Which method fits this mixture? Choose and justify a method. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- End of module · final check. 6 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 3 questions, 15 min, lesson closed.
Learning goals
Part 1: Can we get the water back?
- Explain vaporisation, condensation and component destinations
- Explain the separate roles of apparatus and coolant
Part 2: What if both liquids can escape?
- Explain column enrichment and compare changing fractions
Part 3: Which method fits this mixture?
- Select and justify a method using supplied properties and product goals
Misconceptions to listen for
- “The distillate is cooling water.” — Coolant and sample remain in separate tubes. The receiver collects condensed sample.
- “Water vapour is visible white smoke.” — Water vapour is invisible. Visible outlet drops are condensed liquid.
- “A sealed receiver prevents water escaping safely.” — Sealing a heated apparatus risks pressure build-up. Keep a route to the atmosphere.
- “All 120 g of solution is water.” — Solution mass includes solvent and solute. Find the initial water before subtracting collected water.
- “The collected liquid comes from the coolant.” — The sample vaporises in the flask; the cooling jacket removes heat without mixing.
- “Evaporation alone collects the water.” — Evaporation into the room has no condenser or receiver to recover it.
- “Salt disappears during distillation.” — Salt stays in the remaining solution; water changes container and state.
- “The jacket drains into the receiver.” — The jacket is a separate coolant circuit, surrounding the inner sample tube.
- “The column is a filter.” — Both liquids can vaporise. Packing supports repeated condensation and vaporisation.
- “Exchange receivers while heated vapour still flows.” — After heat is off, residual vapour can still condense. Let it drain before exchange.
Scope
0620 12.4.1(d/e): simple and fractional distillation; bounded12.4.2 method selection. Nonvolatile salt solution and a hypothetical miscible non-azeotropic A/B mixture. No petroleum fractions, complete purity testing or quantitative equilibrium.