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Will the pH of water be same at 4^(@)C a...

Will the pH of water be same at `4^(@)C` and `25^(@)C` ? Explain.

Text Solution

Verified by Experts

At `25^(@)C` ionic product of water `(K_(w))`
`=1xx10^(-14)`
`:.[H^(+)]xx[OH^(-)]=1xx10^(-14)`
or `-log[H^(+)]=log[OH^(-)]=14`
`pH+pOH=14`
it is neutral compound so in it `pH=pOH=7` and at `25^(@)C` .On decreasing the temperature `K_(w)` decreases (since dissociation of water into `H^(+)` and `[OH^(-)]` ions is endothermic ,according to Van't Hoff equation).so `pK_(w)` increase.Hence at `4^(@)C` is greater than at `25^(@)C` and at greater `pK_(w)` .`pH` will be greater i.e, at `4^(@)C pH` of water is greater than `7`.
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Knowledge Check

  • The pH of water at 25^(@)C is nearly

    A
    2
    B
    7
    C
    10
    D
    12

  • The pH of pure water at 80^(@)C will be

    A
    `gt7`
    B
    `lt7`
    C
    `=7`
    D
    cannot be predicted

  • The pH of pure water at 25^(@)C and 35^(@)C are 7 and 6 respectively. What is the heat of formation of water from H^(+) and OH^(-) ?

    A
    `84.55 kcal mol^(-1)`
    B
    `-84.55kcal mol^(-1)`
    C
    `74.55 kcalmol^(-1)`
    D
    `-74.55 kcal mol^(-1)`