The size of a particle in a colloidsal solution is

Options

A. of the order of molecular size `(1 mmu)`
B. greater than `1 mmu`
C. within the range `1mu-1mmu`
D. none of these

Answer

C

Explanation

Range of diameters of colloidal particles is between `1` and `1000nm(10^(-9))` to `(10^(-6)m)` or `(1mmu "to" 1mu)` .
Colloidal particles have an enormous surface area per unit mass (or per gram) as a result of their small size. Consider a cube with `1` cm side. It has a total surface area of `6cm^(2)` . If it were divided equally into `10^(12)` cubes, the cubes would be the size of large colloidal particles and have a total surface area of `60,000cm^(2)` or `6cm^(2)` .
`10^(12)` cubes have volume `1cm^(3)`
`1` cube has volume `(1)/(10^(12))cm^(3)`
i.e. `(side)^(3)=10^(-12)cm^(3)`
side `=10^(-4)cm`
surface area `=6(side)^(2)`
`=6xx10^(-8)cm^(2)`
Thus, total surface area of `10^(12)` cubes will be `10^(12)(6xx10^(-8))cm^(2)=60,000cm^(2)`
This enormous surface area leads to some special properties of colloids.