SS3 First Term Chemistry Lesson Note – Soap and Detergent

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WEEK 4

TOPIC: SOAP AND DETERGENT

CONTENT:

1. Soap preparation and structure
2. Action of soap as an emulsifying agent
3. Detergents: preparation, mode of action of soap
4. Differences between soap and detergent

PERIOD 1:  SOAP PREPARATION (Laboratory)

Soaps are saponification products of fats and oils. They are sodium salts of fatty acids. They are usually referred to as soapy detergents.

1. A mixture of about 100cm³ of vegetable oil (palm kernel oil) and 100cm3 of 10% sodium hydroxide solution is boiled and agitated by passing steam until it is homogenous.
2. Saturated solution of sodium chloride (brine) is then added to the slightly cooked mixture, in order to salt out or separate the soap and from the liquid propan-1,2,3 – triol (glycerol).
3. The soap cord obtained is then slightly dried and mixed thoroughly with perfumes and covalent
4. Again, the soap is slightly dried, then pressed before being cut into tablets or bar.

PERIOD 3: ACTION OF SOAP AS AN EMULSIFYING AGENT

If an oil-water mixture in a container is shaken together vigorously, since oil does not dissolve water, the oil will be suspended as tiny droplets in the aqueous layer. This forms what is called an oil-water emulsion. This emulsion is very unstable, on standing; the droplets will coalesce to form the oil layer again. On addition of some soap solution to the oil-water emulsion, the soap molecules will crowd around each oil droplet as shown in the diagram below:

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