7.2 - Preparation of Soap

Materials and Apparatus Required

Chemicals

• Lard (or vegetable oil)
• Potassium hydroxide (KOH)
• Ethanol
• Saturated sodium chloride solution (brine)
• Anti-bumping granules

Apparatus

• Reflux apparatus
• Flask (for reflux)
• Condenser
• Still head
• Thermometer (-10°C to 110°C)
• Filter funnel and filter paper
• Water bath
• Retort stand and clamps
• Safety glasses

Safety Precautions

• Wear safety glasses at all times.
• Potassium hydroxide is corrosive and can cause severe burns to the eyes and skin. Handle it carefully and avoid contact.
• Ethanol is highly flammable. Keep it away from open flames and sources of ignition.
• Handle hot glassware and heated solutions with care to avoid burns. Use heat-resistant gloves when necessary.

Method

1. Add 2.5 g of lard, 2.5 g of potassium hydroxide, and 20 cm³ of ethanol to a flask.
2. Add a few anti-bumping granules to ensure smooth boiling.
3. Set up the reflux apparatus and ensure all joints are properly greased.
4. Reflux the mixture for 20 minutes using a water bath to maintain a gentle boil.
5. After refluxing, remove the ethanol by distillation.
6. Dissolve the residue in about 15 cm³ of hot water.
7. Add this solution to a saturated sodium chloride solution (brine) to precipitate the soap.
8. Filter the soap using a filter funnel and filter paper.
9. Test the soap's lathering properties by shaking a small sample with water.
10. Be sure to wash your hands thoroughly afterwards to remove any residual potassium hydroxide.

Results

• Soap Precipitate: The soap formed a solid precipitate when added to brine.
• Lathering Test: The soap produced lather when shaken with water, indicating successful soap formation.

Example Questions with Answers