What is the [OH^$$-$$] in the final solution prepared by mixing 20.0 mL of 0.050 M HCl with 30.0 mL of 0.10 M Ba(OH)₂?

Equal volumes of three acid solutions of pH 3, 4 and 5 are mixed in a vessel. What will be the H⁺ ion concentration in the mixture?

Calculate the pOH of a solution at 25^oC that contains 1 $$ \times $$ 10^$$-$$10 M of hydronium ions, i.e. H₃O⁺.

A weak acid, HA, has a K_a of 1.00 $$ \times $$ 10^$$-$$5. If 0.100 mol of this acid is dissolved in one litre of water, the percentage of acid dissociated at equilibrium is closest to