The equation for the pH of a substance is pH = –log[H+], where H+ is the concentration of hydrogen ions. What is the approximate pH of a solution if the concentration of hydrogen ions is 5.0 × 10–4 moles per liter?

Substitute the hydrogen ion concentration into pH = −log[H+]: pH = −log(5.0 × 10⁻⁴). Since log(5.0 × 10⁻⁴) is approximately −3.30, the pH is about 3.3, so the correct choice is 3.3.

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