Understanding the Relationship

* Water Autoionization: Water molecules can react with each other, producing hydronium ions (H₃O⁺) and hydroxide ions (OH⁻). This is represented by the equilibrium:

2H₂O ⇌ H₃O⁺ + OH⁻

* Kw: The product of the hydronium and hydroxide ion concentrations is a constant called Kw, which is equal to 1.0 x 10⁻¹⁴ at 25°C.

Kw = [H₃O⁺] [OH⁻] = 1.0 x 10⁻¹⁴

Calculation

1. Know the hydroxide concentration: You're given [OH⁻] = 0.0000125 M, which can be written as 1.25 x 10⁻⁵ M.

2. Solve for the hydronium concentration: Using the Kw equation:

[H₃O⁺] = Kw / [OH⁻] = (1.0 x 10⁻¹⁴) / (1.25 x 10⁻⁵) = 8.0 x 10⁻¹⁰ M

Answer: The hydronium ion concentration in the solution is 8.0 x 10⁻¹⁰ M.