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  4. If 50 mL of 0.1 M HBr is mixed with 50 mL 0.2 M NaOH then find pH of resulting mixture

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Q. If $50\, mL$ of $0.1\, M \,HBr$ is mixed with $50 \,mL \,0.2\, M \,NaOH$ then find $pH$ of resulting mixture

JIPMERJIPMER 2019Equilibrium

Solution:

$\underset{\text{base}}{N _{1} V _{1}} - \underset{\text{acid}}{N _{2} V _{2}}= NV$
$NaOH \,\,\,\,\,\,\,HBr$
$50 \times 0.2 -50 \times 0.1= N \times 100$
$=N=\frac{5}{100} . $
$\left[ OH ^{-}\right] =N $
$\left[ OH ^{-}\right] =5 \times 10^{-2} $
$ P ^{ OH }=-\log \left[ OH ^{-}\right] $
$=-\log \left(5 \times 10^{-2}\right) $
$=2-\log 5=2-0.7$
$P ^{ OH }= 1.3 $
$P ^{ H }+ P ^{ O } H =14 $
$ P ^{ H }=14-1.3 $
$ P ^{ H }=12.7 $