Equilibrium - Result Question 38
####40. What is the $pH$ of the resulting solution when equal volumes of $0.1 M NaOH$ and $0.01 M HCl$ are mixed?
(a) 12.65
(b) 2.0
(c) 7.0
(d) 1.04
[2015 RS]
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Solution:
- (a) g eq of $NaOH=0.1 \times V=0.1 V$
$g$ eq of $HCl=0.01 \times V=0.01 V$
$g$ eq of $NaOH>g$ eq. $HCl$
hence, resultant solution should be basic, hence from the eqn
$M_1 V_1-M_2 V_2=M V$
$0.1 V-0.01 V=M V$
$M=\frac{0.09}{2}=0.045=4.5 \times 10^{-2}$
Now, $pOH=-\log [OH^{-}]$
$=-\log 4.5 \times 10^{-2}=1.34$
$\because pH+pOH=14$
$\therefore pH=14-1.34=12.65$
