Studying saponification reaction for preparation of soap

Aim

To study saponification reaction for preparation of soap.

Apparatus and Chemical

• Two beakers (250 mL)
• Two test tube
• A glass rod
• A measuring cylinder (50 mL)
• Burner
• Stand
• Wire gauge
• Knife
• 20% sodium hydroxide solution : 30 mL
• Distilled water
• Vegetable oil (cotton seed oil, soyabean oil, palm oil) : 20 mL
• sodium chloride (common salt) : 10 g
• Red and blue litmus paper strips.

Procedure

• Take nearly 20 mL of vegetable oil (preferably palm oil) in a 250 mL beaker. Warm it gently to melt, if needed.
• Add 30 mL of 20% sodium hydroxide solution with constant stirring.
• Successively dip the red and blue litmus paper into this reaction mixture. Do you find any change in colour of any litmus paper strip. Note and record your observation.
• Touch the beaker from outside. Is it hot or cold ? Note and record your observation.
• Heat the beaker containing the reaction mixture on a wire gauge with constant stirring till it thickness.
• Add 10 g of common salt to this. Stir the mixture well and allow it to cool.
• Leave the mixture for some time (nearly 24 hours) till the soap set to a semi-solid mass floating on the top a solution.
• Remove the soap cake and cut it into desired shape.

Observations

(i) (a) Change in colour of red litmus paper when dipped into the mixture : …………. (None/Blue)
(b) Change in colour of blue litmus paper when dipped into the mixture : …………. (None/Red)
(ii) The temperature of reaction mixture on adding sodium hydroxide solution to oil : ………. (increases/decreases)

Result and Discussion

On the basis of your observations with litmus paper, find out the nature of soap mixture (acidic/basic). Also comment whether the saponification reaction is exothermic or endothermic.

Precautions

• Stir the reaction mixture carefully so that it does not spill out.
• Use a wire gauge to heat the reaction mixture.
• Let the soap set and float on the spent lye before removing it form the beaker.
• Sodium hydroxide is hydroscopic in nature. Therefore, store it in an air-tight container.
• Sodium hydroxide is highly corrosive in nature. Therefore, handle it carefully.