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A buffer solution is prepared by mixing $0.2 \mathrm{M}$ sodium acetate and $0.1 \mathrm{M}$ acetic acid. If $\mathrm{pK}_{\mathrm{a}}$ for acetic acid is 4.7 , find the $\mathrm{pH}$.
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Verified Answer
The correct answer is:
5.0
Using Henderson's equation,
$\begin{aligned}
& \mathrm{pH}=\mathrm{pK}_{\mathrm{a}}+\log _{10} \frac{[\text { Salt }]}{[\text { Acid }]} \\
& \mathrm{pH}=4.7+\log _{10} \frac{0.2}{0.1} \\
& \mathrm{pH}=4.7+\log _{10} 2=4.7+0.3010=5.001
\end{aligned}$
$\begin{aligned}
& \mathrm{pH}=\mathrm{pK}_{\mathrm{a}}+\log _{10} \frac{[\text { Salt }]}{[\text { Acid }]} \\
& \mathrm{pH}=4.7+\log _{10} \frac{0.2}{0.1} \\
& \mathrm{pH}=4.7+\log _{10} 2=4.7+0.3010=5.001
\end{aligned}$
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