Question

What is the difference between oil/water (O/W) type and water/oil (W/O) type emulsions? Give an example of each type.

Answer 1

Hint: The term ‘emulsion’ in surface chemistry is used to represent a colloidal dispersion in which both the dispersed phase and dispersion medium are liquids. The two liquids involved are otherwise immiscible.
- Dispersed phase means the substance which is distributed in the dispersion medium in the form of colloidal particles and dispersion medium means the substance which is dispersed in the form of colloidal particles.

Complete step by step answer:
- If the term ‘oil’ is used to denote any liquid which is immiscible with water and is capable of forming an emulsion with water, then the different types of emulsions can be classified into two types which are oil in water emulsion and water in oil emulsion.
- In oil-in-water emulsion or (O/ W) emulsion, the dispersed phase is oil and the dispersion medium is water. In other words, the type of emulsion in which water is present in excess can be said to be an oil-in-water emulsion. For example, milk is an oil-in-water emulsion of liquid fat dispersed in water.
- In water-in-oil emulsion or (W/ O) emulsion, the dispersed phase is water and the dispersion medium is oil. In other words, the type of emulsion in which oil is present in excess can be said to be a water-in-oil emulsion. For example, butter is a water-in-oil emulsion of water in butterfat.
Thus, the type of emulsion formed depends upon the relative amounts of the two liquids. Sometimes, small quantities of other substances called emulsifiers are added to stabilize the emulsions.
Some commonly used emulsifiers for oil-in-water emulsions are proteins, gums and soaps whereas for water-in-oil emulsions are long chain alcohols, heavy metal salts of fatty acids etc.

Note: A few applications of emulsions are:
- Asphalt emulsified in water is used in building roads without the requirement of melting the asphalt.
- The cleansing action of soaps for washing clothes is based upon the formation of oil-in-water emulsion.
- Disinfectants like dettol and lysol on mixing with water give oil-in-water emulsions.