The Ph OF NEUTRAL WATER AT `25^(@)C` is `7.0.` As the temperature increases, ionisation of water increases, however the concentration of `H^(+)` ions nad `OH^(-)` ions equal. What will be the ph of puire water at `60^(@)C`?

Options

A. Equal to 7.0
B. Greater than 7.0
C. Less than 7.0
D. Equal to zero

Answer

C

Explanation

The pH of neutral water at `25.^(@)C` is 7.0.
`:." "[H^(+)]=[OH^(-)]=10^(-7)" "(becausepH=-log[H^(+)])`
Now, `K_(w)=[H^(+)]=[OH^(-)]=(1xx10^(-7))^(2)=1xx10^(-14)`
As the temperature increases, ionisation of water increases, thus `[H^(+)]and[OH^(-)]` increases equally. Now
`K_(w)=[H^(+)][OH^(-)]gt1xx10^(-14)" "(because[H^(+)]=[OH^(-)])`
`or" "[H^(+)]^(2)gt1xx10^(-14)`
`:." "[H^(+)]gt1xx10^(-7)andpHlt7`