InterviewSolution
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InterviewSolution
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20 mL of 0.1 M weak acid `HA(K_(a)=10^(-5))` is mixed with solution of 10 mL of 0.3 M HCl and 10 mL. of 0.1 M NaOH. Find the value of `[A^(-)]`//([HA]+[A^(-)])` in the resulting solution :A. `2 xx 10^(-4)`B. `2 xx 10^(-5)`C. `2 xx 10^(-3)`D. `5 xx 10^(-2)` |
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Answer» Correct Answer - A `[H^(+)] = (10 xx 0.3 - 10 xx 0.1)/(10 + 10 + 20) = 0.05` `[HA] = (20 xx 0.1)/(20 + 20) = 0.05` `{:underset(0.05-x)(HAhArr)underset(0.05+x x)(H^(+)+A^(-)):}` Due to common ion effect neglect x w.r.t `0.05` `K_(a) = ((0.5 + x)x)/((0.05-x))=x, :. x = 10^(-5)` `:. ([A^(-)])/([HA]+[A^(-)]) = (x)/(x+0.05)` `(x)/(0.05) = (10^(-5))/(5 xx 10^(-2)) = 2 xx 10^(-4)` |
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