Chemistry For Cleanliness: Soap

Learning outcome:

Soap, its preparation, and classification
Role of Fat and Alkali On The Mixture of Soap and Glycerine
Fatty Acid

Soap

Generally soap is the sodium salt (R-COONa) or Potassium salt (R-COOK) of higher fatty acid. Here R is the alkyl radical. The general formula of R is C_n H_2n+1and the value of n is 12 to 18.

Example: The chemical formula of Sodium and Potassium Stearate soap is C₁₇H₃₅COONa and C₁H₃₅COOK respectively. Sodium hydroxide or potassium hydroxide reacts with oil or fat and produces soap and glycerine. The procedure of making soap and glycerine is called saponiﬁcation.

If NaCl is added to the mixture of soap and glycerine obtained from the saponiﬁcation process, glycerine stays at the bottom of the pot whereas the molecules of soap gather around NaCl and ﬂoats up in the form of cakes. It is called a soap cake. The soap cake is then ﬁltered by strainer and poured into moulds to make soap of different sizes.

Classification

Soap is a detergent which is produced from oil or fat and alkali. It is mainly two types based on uses-

Toilet Soap

The soap which is used for cleaning our skin is called Toilet Soap.

Laundry Soap

The soap which is used for washing our clothes is called Laundry Soap.

Role of Fat and Alkali on The Mixture of Soap and Glycerine

While preparing soap, glycerine is also produced with soap. Fat or alkali may remain with the mixture of soap and glycerine. Soap is separated from these.

If there is excessive oil or fat in the soap during this separation, there remains an oily situation in the soap. When this type of soap is used, it will not make much scum. On the other hand, if there is an excessive amount of alkali in the soap, its use is harmful to our body. For this reason, while making soap in industries, oil or fat and alkali should be used proportionately so that oil or fat and alkali may react completely.

Related: Bleaching Powder and Glass Cleaner

Fatty Acid

When a carboxylic group is connected to a very big carbon chain, that compound is called higher fatty acid. The fatty acid reacts with alcohol or glycerine and produces an ester. If the tri-ester of higher fatty acid and glycerine is in the liquid state it is called oil and if in the solid state then it is called fat. Example:

a) Stearic Acid is a saturated fatty acid obtained from the fat in animal bodies. There is carbon-carbon single bond in saturated fatty acid where there is no double or triple bond in it.

b) The oil obtained from olive is called olive oil and olic acid is obtained from olive oil. It is an unsaturated fatty acid. There is carbon-carbon double or triple bond in unsaturated fatty acids.

The quantity of alkali or other bad stuff is more in laundry soap and no scent or antibacterial material is added to it. On the other hand, the quantity of alkali or other bad stuff is less in toilet soap and scent or antibacterial material is added to it.