InterviewSolution
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InterviewSolution
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Which of the following represents the correct order of increasing `pK_a` values of the given acids?A. `HClO_4lt HNO_3 lt H_2CO_3 lt B(OH)_3`B. `HNO_3 lt HClO_4 lt B(OH)_3 lt H_2CO_3`C. `B(OH)_3 lt H_2CO_3 lt HClO_4 lt HNO_3`D. `HClO_4 lt HNO_3 lt B(OH)_3 lt H_2CO_3` |
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Answer» Correct Answer - A More the `pK_a` value, weaker is the acid. `HClO_4` is a stronger acid than `HNO_3` (almost same electronegativity of N and Cl, but higher oxidation state of Cl In `HClO_4` than N in `HNO_3`). Both `H_2 CO_3 and B(OH)_3` are very weak acids. `CO_3^(2-)` (from `H_2CO_3`) is resonance stabilized while no such resonance is possible in `[B(OH)_4]^(-)` (from `H_3BO_3`) `H_2CO_3 (aq) hArr 2H^(+) (aq) + CO_3^(2-)(aq)` `B(OH)_3(aq) +H_2O (l) hArr [B(OH)_4]^(-)(aq) + H^(+)(aq)` Thus, correct order of acid strength is `B(OH)_3 lt H_2CO_3 lt HNO_3 lt HClO_4` Order of increasing `pK_a` values `B(OH)_3 gt H_2CO_3 gt HNO_3 gt HClO_4` |
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