question_answer

Will \[pH\] of water be same or different at \[4{}^\circ C\]and \[25{}^\circ C\]? Explain.

Answer:

                \[pH\] of water will be different at these temperatures. Rather \[pH\] of \[4{}^\circ C\]will be more than\[pH\] at \[25{}^\circ C\]. Actually, for water (neutral): \[[{{H}^{+}}]\times [O{{H}^{-}}]={{K}_{w}}={{10}^{-14}}\] at \[25{}^\circ C\] Similarly, \[pH\times pOH=p{{K}_{w}}=14\] at \[25{}^\circ C\] or \[pH=pOH\,=7\] (\[\because \] Water is neutral and\[pH=pOH\]) On increasing the temperature, dissociation of water increases and so is the value of \[{{K}_{w}}\]. This means that at lower temperature (say \[4{}^\circ C\]), the value of \[{{K}_{w}}\] will decrease or\[p{{K}_{w}}\]  will be more than 14. This also means that at lower temperature, the value of \[pH\] (or\[pOH\] ) will be more than 7.