Question

Which of the following statements given about emulsions is incorrect?
A.The droplets in emulsions are often negatively charged and can be precipitated by electrolytes.
B.Emulsion can be diluted with any amount of the dispersed liquid. On the other hand, the dispersion medium when mixed, forms a separate layer.
C.Emulsions can be broken down into constituent liquids by heating, freezing, centrifuging etc.
D.Emulsions also show Brownian movement and Tyndall effect.

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.
The 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:
In oil-in-water emulsion, the dispersed phase is oil and the dispersion medium is water. In water-in-oil emulsion, the dispersed phase is water and the dispersion medium is oil.
Just like colloidal soils, emulsions too can be coagulated or precipitated by the addition of electrolytes containing multivalent positive ions as the dispersed particles or globules in emulsions are negatively charged. Thus, statement A is correct.
Emulsions can be separated into their constituent liquids by boiling, freezing, centrifuging, electrostatic precipitation by the addition of large amounts of electrolytes to precipitate out the dispersed phase or by the chemical destruction of the emulsifier. For example, cream can be separated from milk by centrifugation. So, statement C is correct.
Just like colloidal sols, emulsions can also exhibit the mechanical property of the Brownian movement and the optical property of the Tyndall effect. Thus, the statement D is correct.
The dilution of emulsions can be done by adding any amount of the dispersion medium. That is, oil-in-water emulsions can be diluted by adding any amount of water and water-in-oil emulsions can be diluted by adding any amount of oil. But, if the dispersed phase is added into the emulsion, it will form a separate layer.

So, statement B is incorrect.

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 an oil-in-water emulsion.
-Disinfectants like dettol and lysol on mixing with water give oil-in-water emulsions.