Studying saponification reaction for preparation of soap
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)
- Wire gauge
- 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.
- 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.
(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.
- 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.