scale for measuring hydrogen ion concentration in a solution is called pH scale. (The ‘p’ in pH stands for ‘Potenz’. In German Language ‘Potenz’ is power). pH value of a solution is simply a number which is indicates the acidic or basic nature of a solution.

The pH of neutral solutions is 7. Values less than 7 on the pH scale represent an acidic solution. As the pH value increases from 7 to 14, it represents a decrease in H₃O⁺ ion concentration or an increase in OH^- ion concentration in the solution. pH value of a solution above ‘7’ represents a basic solution.