Chemical and Ionic Equilibrium 2 Question 81
79. How many moles of sodium propionate should be added to $1 \mathrm{~L}$ of an aqueous solution containing 0.020 mole of propionic acid to obtain a buffer solution of $\mathrm{pH} 4.75$ ? What will be $\mathrm{pH}$ if 0.010 moles of $\mathrm{HCl}$ are dissolved in the above buffer solution? Compare the last $\mathrm{pH}$ value with the $\mathrm{pH}$ of $0.010 \mathrm{M} \mathrm{HCl}$ solution. Dissociation constant of propionic acid, $K_{a}$ at $25^{\circ} \mathrm{C}$ is $1.34 \times 10^{-5}$.
(1981, 4M)
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Solution:
- For acidic buffer, the Henderson’s equation is
$$ \begin{gathered} \mathrm{pH}=\mathrm{p} K_{a}+\log \frac{(\text { mole of salt })}{(\text { mole of acid })} \
