Answer to Question #115258 in Chemistry for tristan

Question

What is the hydroxide-ion concentration of an aqueous solution having a pH of 4.72?

Answer 1

Solution:

pH = 4.72

The hydronium ion concentration can be found from the pH:

pH = − log [H₃O⁺]

Thus:

[H₃O⁺] = 10^−pH

[H₃O⁺] = 10^−4.72 = 1.906×10⁻⁵

[H₃O⁺] = 1.906×10⁻⁵ M

The hydroxide ion concentration can be calculated using the K_w constant:

K_w = [H₃O⁺]×[OH⁻] = 1.0×10^-14

Therefore,

[OH⁻] = K_w / [H₃O⁺]

[OH⁻] = (1.0×10⁻¹⁴) / (1.906×10⁻⁵) = 5.246×10⁻¹⁰

[OH⁻] = 5.25×10⁻¹⁰ M

Answer: [OH⁻] = 5.25×10⁻¹⁰ M