(i) Derive the relation between pH and pOH
(ii) Give three uses of emulsions.

Explanation

(i) `" "pH=-log_(10)[H_(3)O^(+)]" "………..(1)`
`pOH=-log_(10)[OH^(-)]" "…………..(2)`
Adding equations (1) and (2),
`pH+pOH=(-log_(10)[H_(3)O^(+)])+(-log_(10)[OH^(-)])`
`=-[(log_(10)[H_(3)O^(+)])+(log_(10)[OH^(-)])]`
`pH+pOH=-log_(10)[H_(3)O^(+)][OH^(-)]`
`[H_(3)O^(+)][OH^(-)]=K_(W)`
`:." "pH+pOH=-log_(10)K_(W)`
`pH+pOH=pK_(W)" "[because pK_(W)=-log_(10)""^(K_(W))]`
At `25^(@)C`, the ionic product of water `K_(W)=1xx10^(-14)`.
`pK_(W)=-log_(10)10^(-14)=14log_(10)=14`
`pK_(W)=14`
`:. pH+pOH=14" at "25^(@)C`.
(ii) 1. The cleansing action of soap is due to emulsions.
2. It is used in the preparation of vanishing cream.
3. It is used in the preparation of cold liver oil.