Question

Calculate pH of a saturated solution of `Mg(OH)_(2)`. `(K_(SP)for Mg(OH)_(2)=8.9xx10^(-12))`

Answer 1

Let solubility of `Mg(OH)_(2)` be S mol `litre ^(-1)`
`Mg(OH)_(2)hArr underset(S)(Mg^(2+))+underset(2S)(2OH^(-))`
`:. [Mg^(2+)][OH]^(2)=K_(SP)`
`4S^(3)= 8.9xx10^(-12)`
`:. S = 1.305xx10^(-4)"mol liltre"^(-1)`
`:. [OH^(-)]=2xx1.305xx10^(-4)"mol litre"^(-1)`
`:. pOH=3.5832`
`pH = 10.4168`