Separation Techniques Flashcards

All 5 cards in this deck

What are the steps to obtain pure water from a salt solution by simple distillation?
e.g. sea water

1. Heat the solution — the water boils/evaporates, leaving the salt behind.
2. The steam (water vapour) passes into the condenser.
3. The vapour condenses to form pure water, which is collected.

What are the steps to obtain crystals of a salt from its solution?
e.g. copper sulfate solution

1. Heat the solution (e.g. using a water bath) to evaporate some water and concentrate it — do not evaporate all the water.
2. Leave to cool so crystals form.
3. Filter off the copper sulfate crystals and leave to dry.

True or false? Filtration can be used to separate a dissolved salt from its solution.

False. Dissolved substances pass straight through the filter paper; filtration only separates an insoluble solid from a liquid.

What are the steps to separate two liquids that mix completely, using fractional distillation?

e.g. a mixture of liquid A (boiling point 43 °C) and liquid B (boiling point 103 °C)

1. Heat/boil the mixture.
2. The liquid with the lower boiling point boils off first and rises up the column — A (43 °C).
3. Its vapour is condensed by the condenser and collected; B stays in the flask.

When is fractional distillation needed instead of simple distillation?

When the liquids in a mixture have boiling points close together. Simple distillation only works for getting a liquid out of a solution, or for liquids with very different boiling points.