Barium hydroxide is a base that is sometimes used for titrating acids. When using it, you need to know the actual concentration of hydroxide ion in the solution. What are the molar concentrations of H₃O⁺ and OH^– in 0.0030 m Ba(OH)₂(aq) at 25°C?

ANTICIPATE Because the compound provides OH^– ions, these ions will be present in overwhelming concentration, but nevertheless there must also be a tiny concentration of H₃O⁺ ions to maintain the value of K_w.

PLAN Most hydroxides of Groups 1 and 2 can be treated as fully dissociated into ions in aqueous solution. Decide from the chemical formula how many OH^– ions are provided by each formula unit and calculate the concentrations of these ions in the solution. To find the concentration of H₃O⁺ ions, use the water autoprotolysis constant Kw = [H₃O⁺][OH^–].