CBSE Class 9 Answered

The topic of pH is not in Class IX. It is in Class X and that too in Class X only the concept is there and not the numericals.

pH = - log [H⁺]

   or

pH = - log [ H₃O⁺]

[H⁺] and [ H₃O⁺] is the concentration of the ions in the solution.

In the question you will be given either the concentration and you will have to find the pH OR you will be given the pH and you will have to find the concentration.

Example: Find the pH of 10^-3 M HCl solution.

Here, the concentration is given.

[H⁺] = 10^-3 M

Now calculate log [H⁺]

log [H⁺] = log ( 10^-3 )

               = -3

Now, pH = - log [H⁺]

                = - (-3)  = +3

Example: The pH of a solution is 2. Calculate the concnetration of H⁺ ions.

pH = - log [H⁺]

2 = - log [H⁺]

log [H⁺]= -2

[H⁺] = 10^-2 M