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InkFlaskCambridge IGCSE

Separate · Chemistry

Condenser

What it is for

Cools a vapour back to a liquid; cold water flows through its jacket.

Mistake to avoid Connecting the water to enter at the top: it should go in at the bottom and out at the top, so the jacket stays full of cold water.

Drawn in ink: the site's lab kit has no model of it yet, so the one at school may look a little different.

How it is asked

  • Label a simple distillation diagram: flask, thermometer, condenser, water in, water out and the distillate.
  • State that cold water enters at the lower end and leaves at the upper end, so the jacket stays full of cold water.
  • Explain what happens inside: the vapour is cooled and condenses back to a liquid, the distillate.

Exam-style question

Pure water is obtained from sea water by simple distillation, using a flask, a thermometer and a condenser.

  1. Why does the cold water enter the condenser at the lower end?
  2. The thermometer stays at 100 °C while the distillate collects. What does this show?
  3. The heating is stopped before the flask boils dry. What is left in the flask?
Show what a good answer says
  1. So the jacket fills completely and cools the whole inner tube; water let in at the top runs out before the jacket is full.
  2. The distillate is pure water: a pure substance boils at a fixed temperature, and pure water boils at 100 °C at normal pressure.
  3. A more concentrated salt solution: the water distils off, but the dissolved salts have very high boiling points and stay behind.

Teaching points for checking your own answer, not official Cambridge marks.

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