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

Explanation

A relation between `pH and pOH` can be established using their following definitions
`pH=-log_(10)[H_3 O^+]" "…(1)`
`pOH=-log_(10)[OH^-]" "…(2)`
Adding equation (1) and (2)
`pH+pOH=-log_(10)[H_3 O']-log_(10)[OH^-]`
`=-(log_(10)[H_3O^+][OH^-] +log_(10)[OH^-])`
`pH+pOH=-log_(10)[H_3 O^+][OH^-]`
`[because loga+logb=log ab]`
We know that `[H_3O^+][OH^-]=K_w`
`rArr pH+pOH=-log_(10)K_w`
`rArr 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)=14 log_(10)10`
`=14`
`therefore (2) rArr therefore ` At `25^@ C, pH +pOH=14`