What is the significance of wanting to know what the pH of a solution is?

pH is an important parameter for many reactions to take place in solution and in biological systems. It is related to the concentration of H⁺ ions through the following expression:

pH = 1/[H⁺] = - log [H⁺]

Wanting to know the pH of a solution is equivalent to knowing the amount of hydrogen ions present. But the pH scale is more convenient than the concentration scale because pH usually takes values between 0 and 14.

When pH <7 the solution is acid. When the solution is neutral (like pure water). When pH> 7 the solution is basic.