Although the pH scale is very useful, it does have some limitations.

• The pH value on the scale does not give an accurate indication of the relative strength of the solution.
• The pH value for 1N solution of strong acid is 0 on the pH scale. Hence, the pH values of strong acid solutions with concentrations of 2N, 3N, 5N, onwards would be negative.
• Using Hammett acidity functions is a better alternative to using the pH scale for solutions with higher concentrations.