Question

We study colloids as part of surface phenomena because

• A. Colloids are a heterogeneous system in which phase boundaries exist
• B. Colloids are homogenous
• C. Colloids have a large surface area and this gives rise to residual forces which are characteristic of such boundaries
• D. All of the above

Answer 1

Answer: (A), (C)

The correct options are
A Colloids are a heterogeneous system in which phase boundaries exist
C Colloids have a large surface area and this gives rise to residual forces which are characteristic of such boundaries

We define colloids to be a heterogeneous mixture consisting of two phases in which, the particle size of dispersed phase is between 1 – 1000 nm. Think of a cube of sugar of side 1 cm. It will have a surface area of 6 $c{m}^2$.

If we cut this into 2 equal halves, we bring in an “added” surface area. Now, will the surface area increase, if we increase the cuts? Definitely it will. Now what will happen to the total surface area of the fine particles if we powder the pieces into nano partcles like this?


The surface area will increase by a huge margin. Sometimes, it reaches to the tune of acres/mol.
Whenever we encounter interfaces, we see that there is a case for residual forces. This gives rise to interesting “surface” phenomena and that is the reason why we study colloids as part of ‘surface chemistry’.