Question

Given an aqueous solution in which the `[H^+]=5.0*10^-3` `M`, what is the molar hydroxide ion concentration?

Answer 1

`[HO^-]=10^(-11.7)=2.0xx10^-12*mol*L^-1`

Explanation:

The easiest way to approach this problem is to use logarithms, and use the relationship:

`pH + pOH=14`

This is specified for aqueous solution under standard conditions.

So `[H_3O^+]=5xx10^-3*mol*L^-1`, and thus,

`pH=-log_10(5xx10^-3)=2.30`

And thus `pOH=11.70`,

and thus `[HO^-]=10^(-11.7)=2.0xx10^-12*mol*L^-1`