Question

What mass of potassium hydroxide, `KOH`, is required to make `250` `cm^3` of a `0.5` `M` solution?

Answer 1

`250` `cm^3` = `0.25` `dm^3` (= `0.25` `L`)

For a solution, `C=n/V` (concentration = number of moles/volume). Rearranging, `n=CV=0.50xx0.25=0.125` `mol`

We need `0.125` `mol` of KOH and the molar mass of KOH is `56.1` `g` `mol^-1`, so `56.1xx0.125=7.0` `g`. We need `7.0` `g` of KOH.