MCQ
For preparing a buffer solution of $pH=6$ by mixing sodium acetate and acetic acid, the ratio of the concentration of salt and acid should be $({K_a} = {10^{ - 5}})$
- A$1\,\,:\,\,10$
- ✓$10\,\,:\,\,1$
- C$100\,\,:\,\,1$
- D$1\,\,:\,\,100$
✓
Answer
Correct option: B.
$10\,\,:\,\,1$
(b) ${K_a} = {10^{ - 5}}$ ; $pH = 6$
$pH = - \log {K_a} + {\rm{log}}\frac{{{\rm{[Salt]}}}}{{{\rm{[Acid]}}}}$ ;$6 = - {\rm{log}}{10^{ - 5}} + {\rm{log}}\frac{{{\rm{[Salt]}}}}{{{\rm{[Acid]}}}}$
$6 = 5{\rm{log}}10 + {\rm{log}}\frac{{{\rm{[Salt]}}}}{{{\rm{[Acid]}}}}$; $6 = 5 + {\rm{log}}\frac{{{\rm{[Salt]}}}}{{{\rm{[Acid]}}}}$
${\rm{log}}\frac{{{\rm{[Salt]}}}}{{{\rm{[Acid]}}}} = 6 - 5 = 1$; $\frac{{{\rm{[Salt]}}}}{{{\rm{[Acid]}}}} = \frac{{10}}{1}$
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