Making of soap:

1. Principle

Oil and sodium hydroxide are boiled and hydrolyzed into higher fatty acid sodium and glycerin, and the former is processed and formed Then there's soap.

2. Supplies

One 150 and 300 ml beaker, glass rod, alcohol lamp, asbestos net, tripod, lard (or other animal and vegetable fats or oils), NaOH, 95% alcohol, saturated salt water.

3. Operation

(1) In a 150ml beaker, put 6 grams of lard and 5ml of 95% alcohol, and then add 10ml of 40% NaOH solution. Stir with a glass rod to dissolve (heat over low heat if necessary).

(2) Place the beaker on an asbestos mesh (or in a water bath), heat over low heat, and stir constantly with a glass holder. During the heating process, if the alcohol and water are reduced by evaporation, they should be replenished at any time to maintain the original volume. For this purpose, 20ml of a mixture of alcohol and water (1:1) can be prepared in advance for addition.

Take out a few drops of the sample from the rod and put it into the test tube. Add 5 to 6 ml of distilled water to the test tube and heat and shake. When left to stand, if grease separates, it indicates that the saponification is incomplete. Alkali solution can be added dropwise to continue saponification.

(4) Slowly add 20ml hot distilled water to the completely saponified viscous liquid, and stir to make them dissolve. Then slowly pour the viscous liquid into 150ml of hot saturated salt solution and stir while adding. After standing, the soap will salt out and float. After all the soap has separated and solidified, it can be taken out with a glass rod, and the soap is ready.

4. Description

(1) Oil is not easily soluble in alkaline water. Alcohol is added to increase the solubility of oil in alkali solution and speed up the saponification reaction.

(2) If a water bath is not used for heating, a small fire must be used.

(3) During the saponification reaction, the original volume of the mixture must be maintained, and the mixture in the beaker must not be boiled dry or spilled out of the beaker.

5. Reaction

Industrial soap making uses animal fatty acids to react with alkali:

RCOOH+NaOH------RCOONa+H2O

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Note: Saponification reaction: hydrolysis reaction of oil under alkaline conditions.