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Q.
The pH of a $ 10^{-10}M\,NaOH $ solution is:
Uttarkhand PMTUttarkhand PMT 2006
Solution:
When the solution is very dilute,
the concentration of $OH ^{-}$ produced from water cannot be neglected.
Hence, $\left[O H^{-}\right]=10^{-10}+10^{-7}$ (obtained from water)
$=10-7(0.001+1)$
$\therefore p O H=-\log \left[O H^{-}\right]$
$=-\log \left(1.001 \times 10^{-7}\right)$
$=7-0.01=6.99$
$\therefore p H=14-p O H$
$=14-6.99=7.01$