Write names of two methods to measure approximate pH of aqueous solution.

Approximate methods to measure pH are those methods which give the general idea about the basicity and acidity of a given solution.

Two such methods are:

1. Litmus paper: if the colour of litmus paper changes from blue to red it indicates the acidic nature and if the colour of litmus paper changes from red to blue it indicates basic nature. Thus it is an approximate method.

2. pH paper: pH paper is dipped in the solution whose pH is to be determined. There occurs a colour change. By observing the colour of the pH paper, we can get a general idea of the pH of the solution.