Understanding the Relationship

* Water Auto-ionization: Water molecules can react with each other to form hydronium ions (H₃O⁺) and hydroxide ions (OH⁻). This process is called auto-ionization.

* Equilibrium Constant: The equilibrium constant for this reaction (Kw) is 1.0 x 10⁻¹⁴ at 25°C. This means:

* [H₃O⁺] * [OH⁻] = 1.0 x 10⁻¹⁴

Calculation

1. Use the Kw expression: We know the concentration of hydronium ions ([H₃O⁺] = 1.5 x 10⁻⁵ M). We can use the Kw expression to find the hydroxide ion concentration ([OH⁻]):

(1.5 x 10⁻⁵ M) * [OH⁻] = 1.0 x 10⁻¹⁴

2. Solve for [OH⁻]:

[OH⁻] = (1.0 x 10⁻¹⁴) / (1.5 x 10⁻⁵ M) = 6.67 x 10⁻¹⁰ M

Answer: The concentration of hydroxide ions is 6.67 x 10⁻¹⁰ M.