(i) The rate constant for a first order reaction is `1.54 times 10^(-3)s^(-1)`.
Calculate its half life time.
(ii) Explain about protective action of colloid.

Explanation

(i) We know that. `t_(1//2)=0.693//k`
`t_(1//2)=0.693//1.54 times 10^(-3)s^(-1)=450s`
(ii) 1. Lyophobic sols are precipitated readily even with small amount of electrolytes. But they are stabilised by the addition of small amount of lyophillic colloid.
2. A small amount of gelatine sol is added to gold sol to protect gold sol.
3. Gold number is a measure of protecting power of a colloid. Gold number is defined as the number of milligrams of hydrophillic colloid that will just prevent the precipitation of 10 ml of gold sol on the addition of 1ml of 10% NaCl solution. Smaller the gold number, greater the protective power.