Q10 / 160 · AP EAMCET 2018 (22 Apr Shift 1) · Chemistry

If the $\mathrm{p} K_a$ of acetic acid and $\mathrm{p} K_b$ of dimethylamine are 4.76 and 3.26 respectively, the $\mathrm{pH}$ of dimethyl ammonium acetate solution is

  • Correct answer
    A
    7.75
  • B
    6.75
  • C
    7.0
  • D
    8.5

Solution

$\begin{aligned} & \text { } \begin{aligned} \mathrm{pH}= & 7+\frac{1}{2}\left[\mathrm{p} K_a-\mathrm{p} K_b\right] \\ \text { Here, } \mathrm{p}_a & =4.76, \mathrm{p} K_b=3.26 \\ & =7+\frac{1}{2}[4.76-3.26] \\ & =7+\frac{1}{2}[1.50] \\ & =7+0.75=7.75\end{aligned}\end{aligned}$

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

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