Emulsions:-

Emulsions are the colloidal solutions of liquid. Both the dispersed phases as well as dispersion medium are the liquids. The two liquids should not be miscible with each other. To stabilize the emulsions a suitable reagent is added which is called emulsifier of emulsifying agent. the common substance used as emulsifier or emulsifying agent are gym, soap, glass powder etc. For example:

The process of decomposing an emulsion back into constituent liquids is called de-emulsification.

Cleaning action of soap:- the cleaning action of soap is due to its tendency to act as emulsions. A soap (sodium stearate = Ch₃ (CH₂)₁₅CH₂–COO^-Na⁺) is composed of long chain of alkyl group called tail and a polar part called head.

The dirt is bind to clothes through the fat or grease particles. The hydrocarbon part (Tail) of the soap molecules is soluble in grease (oil) and polar part (head) is soluble in water. due to similar charge the oil drops breaks up and goes into water as emulsions, the soap molecule acts as emulsifying agent. thus small oil (grease) particles having dirt are washed away with water.

Type of Emulsions:- Emulsions can be classified in two types:

1. Oil-in-water emulsions:- in this type of emulsions oil acts as dispersed phase and water acts as dispersion medium e.g. milk vanishing cream etc. Aluminium oleate is used as emulsifier in o/w emulsions.
2. Water-in-oil emulsions:- in this type of emulsions water acts as dispersed phase and oil (organic solvent) acts as dispersion medium. e.g. butter, cod liver oil, cold cream etc. Gelatin is used as emulsifier in w/o emulsions.

Tests to distinguish Emulsions:- Following tests are employed to test the emulsions:

1. Dye test:- some oil soluble dye is added to the emulsions if the background becomes colored, the emulsion is water –in –oil emulsion and if the colored droplets are seen, it is oil – in water type emulsion.

Dilution test:- if the emulsion can be diluted with water, it is oil –in – water type emulsion and if water forms the separate layer, it is water – in – oil type emulsion.