Purification Techniques: Crystallization

Purification Techniques: Crystallization

Introduction

Crystallization is a technique used to purify solids by selectively dissolving impurities from the solid. Crystallization is based on the principle that different substances have different solubilities in a given solvent. The desired solid is dissolved in a solvent in which it is less soluble, and the impurities are dissolved in a solvent in which they are more soluble. The solution is then cooled, and the desired solid crystallizes out of the solution.

Basic Concepts

Solubility: The amount of a substance that can be dissolved in a given solvent at a given temperature. Crystallization: The process of forming crystals from a solution.
Crystallization temperature: The temperature at which a substance crystallizes from a solution. Crystal habit: The shape of a crystal.

Equipment and Techniques

The following equipment is required for crystallization:
A beaker A stirring rod
A filter funnel A filter paper
* A drying oven
The following steps are involved in crystallization:
1. The desired solid is dissolved in a solvent in which it is less soluble.
2. The solution is heated to the crystallization temperature.
3. The solution is stirred to prevent the formation of large crystals.
4. The solution is cooled to the crystallization temperature.
5. The crystals are filtered from the solution.
6. The crystals are washed with a solvent in which they are less soluble.
7. The crystals are dried in a drying oven.

Types of Experiments

There are two types of crystallization experiments:
Static crystallization: The solution is cooled slowly to the crystallization temperature. Dynamic crystallization: The solution is cooled rapidly to the crystallization temperature.

Data Analysis

The following data can be collected from a crystallization experiment:
The yield of the crystallization: The amount of desired solid that is recovered from the solution. The purity of the crystallization: The amount of impurities that are present in the desired solid.
* The crystal habit of the crystallization: The shape of the crystals.

Applications

Crystallization is used to purify a wide variety of solids, including:
Pharmaceuticals Food additives
Dyes Pigments
* Electronic materials

Conclusion

Crystallization is a powerful technique that can be used to purify a wide variety of solids. The technique is relatively simple to perform, and it can be used to achieve high yields of pure product.