Introduction to Purification of Organic Compounds:
In Class 11 Chemistry, understanding the methods of purification of organic compounds is crucial as it forms the basis for further study of organic chemistry. Organic compounds often contain impurities, and various techniques are used to purify them. Here’s a detailed summary of the methods of purification of organic compounds.
1. Sublimation
Definition: Sublimation is the process where a solid changes directly into a gas without passing through the liquid state.
Use: This method is used for compounds that sublime (e.g., naphthalene, camphor, benzoic acid) and separates them from non-sublimable impurities.
Example: Purification of benzoic acid from impurities.
2. Crystallization
Definition: Crystallization is the process of forming solid crystals from a homogeneous solution.
Use: It separates a pure solid in the form of crystals from a solution. Impurities remain in the solution.
Procedure:
- Dissolve the impure compound in a suitable solvent.
- Filter the hot solution to remove insoluble impurities.
- Cool the solution to form crystals of the pure substance.
- Filter out the crystals and wash them with a small amount of cold solvent.
Example: Purification of sugar from a sugar solution.
3. Distillation
Definition: Distillation involves the separation of components of a mixture based on differences in their boiling points.
Types:
1. Simple Distillation: Used when the difference in boiling points of the components is large (more than 25°C).
2. Fractional Distillation: Used when the difference in boiling points is small.
3. Steam Distillation: Used for separating temperature-sensitive substances that decompose at high temperatures.
Example: Purification of acetone from water using simple distillation.
4. Distillation Under Reduced Pressure (Vacuum Distillation)
Definition: This technique is used when the compounds have very high boiling points or decompose before reaching their boiling point at normal pressure.
Use: By reducing the external pressure, the boiling point of the compound decreases, allowing it to distill at lower temperatures.
Example: Purification of glycerol or certain organic acids.
Read Also: Class 11 Chemistry: Nomenclature of Organic Compounds
5. Chromatography
Definition: Chromatography is a technique used to separate the components of a mixture based on differences in their movement through a stationary phase under the influence of a mobile phase.
Types:
1. Thin Layer Chromatography (TLC): Used for monitoring the progress of reactions, identifying compounds, and checking the purity of compounds.
2. Column Chromatography: Used for purifying larger quantities of compounds.
3. Gas Chromatography (GC): Used for separating volatile compounds.
4. Paper Chromatography: Typically used for separating amino acids and sugars.
Example: Separation of plant pigments by paper chromatography.
6. Differential Extraction
Definition: Differential extraction is used to separate organic compounds from aqueous solutions using solvents in which the compound has a higher solubility than in water.
Procedure:
- The impure compound in water is shaken with a non-miscible organic solvent.
- The organic layer containing the compound of interest is separated using a separating funnel.
Example: Extraction of caffeine from tea.
7. Fractional Crystallization
Definition: This method separates compounds based on differences in their solubility in a solvent at different temperatures.
Use: A mixture of solids is dissolved in a solvent at an elevated temperature. Upon cooling, the less soluble compound crystallizes out first.
Example: Separation of potassium nitrate (KNO₃) from sodium chloride (NaCl) by fractional crystallization.
8. Simple Filtration
Definition: Filtration is a simple technique used to separate an insoluble solid from a liquid.
Use: This method is used when the impurities are insoluble in the solvent, and the pure substance is dissolved in it.
Example: Removal of solid impurities from a liquid solution.
9. Sublimation and Sublimable Compounds:
Sublimable compounds such as iodine, naphthalene, and benzoic acid can be purified by sublimation because they can directly pass from the solid to the gaseous phase without passing through a liquid phase.
General Summary of Methods:
Conclusion:
Purifying organic compounds is a crucial step in organic chemistry to ensure that the substances are free from impurities and suitable for further analysis or use. Each method of purification, whether it be sublimation, distillation, crystallization, or chromatography, is selected based on the physical and chemical properties of the compound, such as volatility, solubility, and thermal stability. Mastering these techniques allows chemists to isolate pure compounds, ensuring accurate study of their structure, reactivity, and properties. By applying the appropriate purification method, one can efficiently obtain high-quality substances for both academic and industrial applications.