Chemical and Ionic Equilibrium - Result Question 137
####79. How many moles of sodium propionate should be added to $1 L$ of an aqueous solution containing 0.020 mole of propionic acid to obtain a buffer solution of $pH 4.75$ ? What will be $pH$ if 0.010 moles of $HCl$ are dissolved in the above buffer solution? Compare the last $pH$ value with the $pH$ of $0.010 M HCl$ solution. Dissociation constant of propionic acid, $K _a$ at $25^{\circ} C$ is $1.34 \times 10^{-5}$.
(1981, 4M)
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Solution:
- For acidic buffer, the Henderson’s equation is
$$ \begin{gathered} pH=p K _a+\log \frac{(\text { mole of salt })}{(\text { mole of acid })} \
