In cae of pure water or any aqueous solution, show that pH+pOH=14. comment on whether this value will be greater than or less than 14 at `0^(@)C and 100^(@)C`.

Explanation

First part:
Second: We know, pH+pOH=`pK_(w) and pK_(w)=-log_(10)K_(w)`
Rise in temperature increases the value of `K_(w)`. Therefore,
`K_(w)(0^(@)C) lt K_(w)(25^(@)C) lt K_(w)(100^(@)C)`
Since `pK_(w)=-log_(10)K_(w),`
`pK_(w)(100^(@)C) lt pK_(w)(25^(@)C) lt pK_(w)(0^(@)C)`
Now, at `25^(@)C, pK_(w)=14`.
Therefore, `pK_(w)(100^(@)C) lt 14 lt pK_(w)(0^(@)C) and pH+pOH (100^(@)C) lt pH+pOH(25^(@)C) lt pH+pOH(0^(@)C)`
Hence, the value of `(pH+pOH)` will be higher at `0^(@)C` than at `25^(@)C`, but it will be lower at `100^(@)C` than at `25^(@)C`.