Question

Calculate the hydroxide ion concentration at 25 in a solution whose pH is 5.78. (kW=1*10_14moldm at25)

Answer 1

Solution:

hydroxide ion = [OH⁻]

pH = −log[H₃O⁺]

Therefore,

[H₃O⁺] = 10^−pH = 10^−5.78 = 1.66×10⁻⁶

[H₃O⁺] = 1.66×10⁻⁶ M

K_w = [H₃O⁺] × [OH⁻]

Therefore,

[OH⁻] = K_w / [H₃O⁺] = (1.0×10⁻¹⁴) / (1.66×10⁻⁶) = 6.02×10⁻⁹

[OH⁻] = 6.02×10⁻⁹ M

Answer: The hydroxide ion (OH⁻) concentration is 6.02×10⁻⁹ M