To study saponification reaction for preparation of soap - Science Practicals

To study saponification reaction for preparation of soap.

Oil or fat when treated with sodium hydroxide solution, gets converted into sodium salt of fatty acid (soap) and glycerol. This reaction is known as saponification. The fatty acid of the glyceride is converted to sodium (or potassium) salt of the acid (soap) and glycerol is produced. For example, stearic acid reacts with NaOH to produce soap and glycerol. 

Materials Required
Castor oil (or cotton seed oil or linseed oil), 20% sodium hydroxide solution, Common salt, Hard glass beaker, Stirrer and Moulds of desired shapes brown freezer paper

Step 1: About 20 ml of castor oil (or cotton seed oil or linseed oil or soyabean oil in place of castor oil) is taken in a 250 ml hard glass beaker.
Step 2: 30 ml of 20% sodium hydroxide solution is added to it.
Step 2: Mixture is heated with continuous stirring for a few minutes (about 5 min. brisk stirring) until a thick mixture is formed.
Step 2: About 5-10 g common salt is added to the reaction mixture while it is still hot and the mixture is stirred.
Step 2: Moulds is lined with brown freezer paper and the mixture is quickly poured in moulds.
Step 2: The moulds are covered and left for about 20-24 hours to cool.
Step 2: The soap is removed from moulds.

1. On heating and continuous stirring oil and sodium hydroxide solution, oil and water layers merge with each other.
2. The resulting mixture becomes thick which on adding common salt and cooling forms a pale yellow cake/mould shaped.
3. When a piece of this material is used to clean an ink spot or glass beaker etc. It gives effects of a soap i.e. it has cleansing effect.

Results and Discussions
By mixing vegetable oil and sodium hydroxide solution in proper ratio and heating the mixture followed by proper cooling we can get soap.

1. Mixture of oil and NaOH solution should not be overheated.
2. NaOH solution should be handled very carefully.
3. Continuous and thorough stirring of the reaction mixture is necessary.

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