A wastewater sample contains 10–5.6 m mol/l of OH

A wastewater sample contains 10^–5.6 m mol/l of OH– ions at 25°C. The pH of this sample is

[H^–1] [OH^–] = 10^–14
[OH^–] = 10^–5.6 m mol/l
= 10^–5.6 × 10^–3 mol/l
= 10^–8.6 mol/l

∴ [H⁺] =	10^–14	= 10^–5.4mol/l
	10^–8.6

pH = –log[H⁺] = – log[10^–5.4] = 5.4.