Thermodynamics and Thermochemistry 2 Question 34
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34. The pH of the solution after Expt. 2 is
======= ####34. The pH of the solution after Expt. 2 is
3e0f7ab6f6a50373c3f2dbda6ca2533482a77bed (a) 2.8
(b) 4.7
(c) 5.0
(d) 7.0
Show Answer
Solution:
- $\mathrm{CH}{3} \mathrm{COOH}+\mathrm{NaOH} \rightarrow \mathrm{CH}{3} \mathrm{COONa}+\mathrm{H}_{2} \mathrm{O}$
$200 \mathrm{mmol} \quad 100 \mathrm{~mol} \quad 0 \quad 0$
$100 \mathrm{mmol} \quad 0 \quad 100 \mathrm{mmol}$
A buffer is now formed.
$$ \begin{gathered} K_{a}=\frac{\left[\mathrm{H}^{+}\right]\left[\mathrm{CH}{3} \mathrm{COO}^{-}\right]}{\left[\mathrm{CH}{3} \mathrm{COOH}\right]}=\left[\mathrm{H}^{+}\right] \ {\left[\because\left[\mathrm{CH}{3} \mathrm{COOH}\right]=\left[\mathrm{CH}{3} \mathrm{COO}^{-}\right]\right]} \ \Rightarrow \quad \mathrm{pH}=\mathrm{p} K_{a}=-\log \left(2 \times 10^{-5}\right)=5-\log 2=4.7 \end{gathered} $$
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