What is the pH of a substance with a hydrogen ion concentration of 1 x 10-3 M?

The pH of the substance is 3.

Explanation:

Given:

Concentration of hydrogen ion, [H⁺] = 10⁻³M

pH = ?

The pH of a solution is a measure of the molar concentration of hydrogen ions in the solution and as such is a measure of the acidity or basicity of the solution.

pH = - log [H⁺]

pH = - log [10⁻³]

pH = 3 log [10]

pH = 3

The pH of the substance is 3 and since the pH is less than 7, the substance is acidic in nature.