InterviewSolution
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InterviewSolution
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Acidic solution is defined as a solution whose `[H^(o+)] gt [overset(Theta)OH]`. Base solution has `[overset(Theta)OH] gt [H^(o+)]`. During acid-base titrations, `pH` of the mixture will change depending on the amount base added. This variation is shown in the form of graph by making plot as titration curves `100mL` of `1.0 M H_(3)A (K_(a_(1)) = 10^(-3), K_(a_(2)) = 10^(-5), K_(a_(3)) = 10^(-7))` is titrated against `0.1M NaOh`. The titration curve is as follows. What is the `pH` at point `A?A. `3`B. `4`C. `5`D. `6` |
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Answer» Correct Answer - B Since `K_(a_(1))` and `K_(a_(2))` are high values therfore point `A, K_(a_(1))` and `K_(a_(2))` are considered. `H_(3)A hArr H^(o+) + H_(2)A^(Theta)` `H_(2)A^(Theta) hArr H^(o+) + HA^(2-)` `K_(a_(1)) xx K_(a_(2)) = ([H^(o+)][HA^(2-)])/([H_(2)A]) [["At equivalence point",],[[HA^(2-)]=,[H_(3)A]]]` `-log K_(a_(1)) - log K_(a_(2)) =- 2log [H^(o+)]` `pK_(a_(1)) + pK_(a_(2)) = 2pH`. `:. pH = (pK_(a_(1)) + pK_(a_(2)))/(2) = (3+5)/(2) = 4` |
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