Q12 / 160 · AP EAMCET 2024 (22 May Shift 2) · Chemistry

100 mL of 0.1 M HA (weak acid) and 100 mL of 0.2 M NaA are mixed. What is the pH of resultant solution? ( $\mathrm{K}_{\mathrm{a}}$ of HA is $10^{-5} ; \log 2=0.3$ )

  • A
    4.7
  • B
    5.0
  • Correct answer
    C
    5.3
  • D
    4.0

Solution

$\mathrm{pH}=\mathrm{pK}_{\mathrm{a}}+\log \frac{[\text { Salt }]}{[\text { Acid }]}$ $\begin{aligned} & \mathrm{pH}=5+\log \frac{[0.2]}{[0.1]} \quad\left[\mathrm{pK}_{\mathrm{a}}=-\operatorname{log\mathrm {K}_{\mathrm {a}}=-\operatorname {log}10^{-5}=5]}\right. \\ & \mathrm{pH}=5+\log 2 \\ & \mathrm{pH}=5+0.3 \\ & \mathrm{pH}=5.3\end{aligned}$

Hence, the correct answer is option: 'C'.

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