1. Objective:
To prepare potassium alum, �, in the laboratory by crystallization.
2. Principle :
Potassium alum is a double salt of potassium sulphate and aluminium sulphate. It is prepared by mixing their solutions in the correct proportion and then concentrating and cooling the solution to obtain crystals.
3. Structure
4. Chemical Reaction Step 1: Formation of aluminium sulphate
Step 2: Formation of potassium alum
5. Chemical Requirements:
- Aluminium hydroxide, 2. �Dilute sulphuric acid, 3. �Potassium sulphate, 4. �Distilled water
6. Apparatus Requirements:
- Beaker 2. Glass rod 3. Measuring cylinder 4. Funnel 5. Filter paper 6. Evaporating Dish 7. tripod Stand 8. wire gauze 9. Burner. 10. Watch glass
7. Procedure:
- Dissolve the required amount of aluminium sulphate in hot distilled water.
- Prepare a solution of potassium sulphate separately.
- Mix the two solutions and stir well.
- Heat the solution gently to concentrate it.
- Allow the concentrated solution to cool slowly.
- Colourless/white crystals of potassium alum separate out.
- Filter the crystals and wash them with a small amount of cold water.
- Dry the crystals between filter papers.
Result: white/colourless, transparent crystals of potassium alum (fitkari), �, were obtained by crystallization.
8. Precautions
- Use dilute sulphuric acid carefully.
- Do not heat the solution strongly or to complete dryness.
- Use only a small quantity of cold water for washing crystals.
- Allow the solution to cool slowly for better crystal formation.
- Handle glassware and hot solutions carefully.
9. Applications of Potassium Alum:
- Used as a mordant in dyeing and printing.
- Used in paper and textile industries.
- Used as an astringent.
- Used in some traditional shaving products to help stop minor bleeding.
- Used for purification of drinking water.
