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  • The dissociation constant of acetic acid is . When <img alt="25 \mathrm{~m

The dissociation constant of acetic acid is x \times 10^{-5}. When 25 \mathrm{~mL} of 0.2 \mathrm{MCH}_3 \mathrm{COONa} solution is mixed with 25 \mathrm{~mL} of 0.02 \mathrm{MCH}_3 \mathrm{COOH} solution, the \mathrm{pH} of the resultant solution is found to be equal to 5 . The value of x is 

Option: 1

10


Option: 2

-


Option: 3

-


Option: 4

-


Answers (1)

best_answer

\mathrm{K}_{\mathrm{a}}=\mathrm{x} \times 10^{-5}

\mathrm{CH}_3 \mathrm{COOH} \rightarrow 0.02 \mathrm{M} \& 25 \mathrm{ml}
\mathrm{CH}_3 \mathrm{COONa} \rightarrow 0.2 \mathrm{M} and 25 \mathrm{ml}

\mathrm{pH}=\mathrm{p}^{\mathrm{K}_{\mathrm{a}}}+\log \frac{[\text { salt }]}{[\text { acid }]}
5=\mathrm{p}^{\mathrm{K}_{\mathrm{a}}}+\log \frac{0.2 \times 25}{0.02 \times 25}=\mathrm{p}^{\mathrm{K}_{\mathrm{a}}}+\log 10
\mathrm{p}^{\mathrm{K}_{\mathrm{a}}}=4
\mathrm{~K}_{\mathrm{a}}=10^{-4}=10 \times 10^{-5}

Hence x=10

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