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20/10/2021 10:07 am
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Which one of the following arrangements represents the correct order of the proton affinity of the given species:
(a) I- < F- < HS- < NH2-
(b) HS- < NH2- < F- < I-
(c) F- < I- < NH2- < HS-
(d) NH2- < HS- < I- < F-
1 Answer
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20/10/2021 10:09 am
Correct answer: (a) I- < F- < HS- < NH2-
Explanation:
The species with the greatest proton affinity will be the strongest base, and its conjugate acid will be the weakest acid. The weakest acid will have the smallest value of Ka. Since HI is a stronger acid than HF which is a stronger acid than H2S, a partial order of proton affinity is
I- < F- < HS-
Since NH3 is a very weak acid, NH2- must be a very strong base. Therefore the correct order of proton affinity is I- < F- < HS- < NH2-