Question

three substances which can be purified through crystallization

Answer 1

large crystals of pure copper sulphate , alum , phitkari

Answer 2

Crystallization is a commonly used technique for the purification of substances. It is a separation technique in which solids are separated from a solution.

When a solid substance is mixed with a liquid and snirred, it dissolves in the fluid. When we keep on adding more and more solid to the liquid, a point comes after which no more solid can be dissolved in the liquid. This point is known as the saturation point, and the solution is called a saturated solution.

In this technique the solvent molecules start evaporating, leaving behind the solutes when the solution is heated in an open container. On cooling this solution, the dissolved solids come out of the solution and crystals of solute start accumulating on the surface of the solution. Now, these crystals can be collected and dried as per the requirement of the product. If a solid is not dissolved in the liquid and is simply mixed in it, then it can be separated by the process of filtration.

The size of crystals formed during this process depends on the cooling rate. If the solution is cooled at a fast rate then, it forms a large number of tiny crystals. Large crystals are formed at slow cooling rates.

Separation of Substances by Crystallization Technique

 Activity:

To understand crystallization more clearly let us perform an activity.

Take 50 ml water in a beaker. Add sugar in it and stir it. Now heat the solution. Repeat the process continuously. After some time there will be a point after no more sugar can be dissolved in water. This stage is the saturation point, and the solution is referred as a saturated solution.

Now filter the sugar with the help of a filter paper. Collect the filtrate in a glass bowl and cool it. We will observe that some fine crystals are formed in the bowl. The process of filtration can separate these crystals. The liquid left after the removal of crystals is known as mother liquor.

Applications of crystallization:

Purification of sea water. Separation of alum crystals from impure samples .In the pharmaceutical industry, crystallization is used as a separation and purification process for the synthesis and isolation of co-crystals, pure active pharmaceutical ingredients (API), controlled release pulmonary drug delivery, and separation of chial isomers.

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