A sample of impure sugar can be purified by using crystallization.
Crystallisation: Crystallisation is a technique to purify an impure sample and obtain pure solid in the form of crystals from its solution.
Process of crystallization of pure sugar from an impure sugar:
Prepare a saturated solution of the given impure sugar sample at room temperature.
This can be done by dissolving impure sugar in water until no more sugar dissolves in it.
Then heat the solution and dissolve more sugar in it to prepare a saturated solution at this higher temperature.
Filter the solution and obtain the filtrate in a beaker.
This will remove the undissolved insoluble impurities in the impure sample of sugar.
Allow the filtrate to cool.
On cooling, sugar crystals will start to appear in the beaker because the saturated solution on heating can hold more sugar than the solution at a lower temperature and thus start to crystallize.
Take a small crystal of sugar and suspend it in the solution with the help of a thread. This crystal acts as a seed crystal and encourages more crystals to separate and eventually seed crystals will grow bigger.
These crystals are pure sugar crystals. The dissolved impurities are left in the solution.
