Question

The hydronium ion concentration in a sample of rainwater is found to be 1.7 × 10⁻⁶ M at 25 °C. What is the concentration of hydroxide ions in the rainwater?

a) 1.7 × 10⁻⁶ M
b) 5.9 × 10⁻⁸ M
c) 5.9 × 10⁻⁷ M
d) 1.7 × 10⁻⁷ M

Answer 1

The hydroxide ion concentration in rainwater, with a given hydronium ion concentration of 1.7 × 10−6 M at 25 °C, can be calculated using the water ion product and is found to be 5.9 × 10−9 M.

Step-by-step explanation:

The concentration of hydroxide ions in the rainwater can be calculated using the relationship between the hydronium ion concentration and the hydroxide ion concentration, which is defined by the ion product constant for water, Kw. At 25 °C, Kw is 1.0 × 10−7 M2.

Since the hydronium ion concentration ([H3O+]) in the rainwater is 1.7 × 10−6 M, we can use Kw to find the hydroxide ion concentration ([OH−]) using the formula Kw = [H3O+][OH−]. Therefore, [OH−] = Kw / [H3O+] which equals (1.0 × 10−7 M2) / (1.7 × 10−6 M), resulting in an [OH−] of approximately 5.9 × 10−9 M. The correct answer for the concentration of hydroxide ions in the rainwater is thus 5.9 × 10−9 M, which corresponds to option b.