Question

What will be the resultant pH when 200 mL of an aqueous solution of HCl (pH = 2) is mixed with 300 mL of an aqueous solution of NaOH (pH = 12)?

• A. 7.8
• B. 5.5
• C. 2.7
• D. 11.3

Answer 1

The correct option is D 11.3

As pH of HCl = 2 So

$\left[\text{HCl}\right]={10}^{-2}\text{M}$

Milliequivalent of $H^{+}$ = 2
pH of NaOH = 12
$\left[{\text{OH}}^{-}\right]={10}^{-2}\text{M}$
Milliequivalent of $O{H}^{-}$ = 3
HCl+NaOH $\rightleftharpoons$ NaCl + ${\text{H}}_{2}O$

${\text{M}}_{\text{eq}}{\text{of OH}}^{-}\text{after reaction}=3-2=1$

$\left[{\text{OH}}^{-}\right]\text{after reaction}=\frac{1}{500}$

= $2\times {10}^{-3}\text{M}$

pOH=$-{\text{log}}_{10}\left[{\text{OH}}^{-}\right]$

=$-{\text{log}}_{10}2\times {10}^{-3}=2.7$

pH = 14-2.7 = 11.3