If a solution has a pH of 8, which statement is true about [OH-] and [H+]?

If a solution has a pH of 8, which statement is true about [OH-] and [H+]?

• A. H+ dominates
• B. H3O+ dominates
• C. OH- are more abundant than H+
• D. H2O dominates

Answer: (C)

At pH 8, the solution is basic, meaning the hydrogen ion concentration is small. The pH tells us [H+] = 10^-8 M. Using the water autoionization constant Kw ≈ 1.0 × 10^-14 at room temperature, the hydroxide concentration is [OH-] = Kw / [H+] = (1.0 × 10^-14) / (1.0 × 10^-8) = 1.0 × 10^-6 M. So [OH-] is 100 times larger than [H+]. Hydronium (H3O+) is just another way to refer to the same hydrogen ions in solution, so it’s not dominating here. The larger concentration of OH- compared to H+ shows why the solution is basic. Therefore, the true statement is that hydroxide ions are more abundant than hydrogen ions.

At pH 8, the solution is basic, meaning the hydrogen ion concentration is small. The pH tells us [H+] = 10^-8 M. Using the water autoionization constant Kw ≈ 1.0 × 10^-14 at room temperature, the hydroxide concentration is [OH-] = Kw / [H+] = (1.0 × 10^-14) / (1.0 × 10^-8) = 1.0 × 10^-6 M. So [OH-] is 100 times larger than [H+].

Hydronium (H3O+) is just another way to refer to the same hydrogen ions in solution, so it’s not dominating here. The larger concentration of OH- compared to H+ shows why the solution is basic. Therefore, the true statement is that hydroxide ions are more abundant than hydrogen ions.