The [H+] of a solution is 1.0 x 10-4 M. Classify the solution as acid, base, or neutral. What is the [OH-] of the solution?

A) Acid; 4

B) Base; 10

C) Acid; 1 x 10 - 10M

D) Base; 1 x 10 - 10M

Solution is acidic with [H⁺] = 1 x 10⁻⁴M = > pH = 4; [OH⁻] = 1 X 10⁻14/1 x 10⁻⁴ = 1 x 10⁻¹⁰

Explanation:

Acidity and Alkalinity of an aqueous solution is defined relative to the relationship between the concentrations of Hydronium ions (H₃O⁺) vs Hydroxide ions (OH⁻) in solution. That is, for pure water at 25°C it is known that [H₃O⁺] = [OH⁻] = 10⁻⁷M for 'neutral' solutions. However, if ...

[H₃O⁺] > 10⁻⁷M = > [OH⁻] < 10⁻⁷M = > the solution is classified as acidic, and if

[H₃O⁺] < 10⁻⁷M = > [OH⁻] > 10⁻⁷M = > the solution is classified as alkaline or basic.

Relating this to pH values where pH = - log[H₃O⁺]

for [H₃O⁺] = 10⁻⁷M = > pH = - log (10⁻⁷) = 7 for neutral solutions

for [H₃O⁺] > 10⁻⁷M = > pH < - log (10⁻⁷) < 7 for acidic solutions

for [H₃O⁺] < 10⁻⁷M = > pH > - log (10⁻⁷) > 7 for basic solutions