## HI vs HOI

Hannah Chew 2A
Posts: 76
Joined: Fri Sep 29, 2017 7:05 am
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### HI vs HOI

So this isn't a hw question, but this is more from the lecture notes. Why is HI a really strong acid, and HOI not as strong? I understand that HI has a long bond length and is long, and I understand that having more oxygens stabilizes the resulting anion. However, when combining these concepts, it would appear that HOI should be stronger because it has an extra oxygen. Why is this not the case? Thank you in advance:)

Curtis Tam 1J
Posts: 105
Joined: Thu Jul 13, 2017 3:00 am

### Re: HI vs HOI

I think this is a topic discussed in 14C. It has to do with the distance between the halogen and hydrogen atom in oxoacids versus binary acids. However, when comparing just HI and HOI alone, I'm not entirely sure how that is determined. Probably we have to look at the pKa's.

Curtis Tam 1J
Posts: 105
Joined: Thu Jul 13, 2017 3:00 am

### Re: HI vs HOI

Hannah Chew 1L wrote:So this isn't a hw question, but this is more from the lecture notes. Why is HI a really strong acid, and HOI not as strong? I understand that HI has a long bond length and is long, and I understand that having more oxygens stabilizes the resulting anion. However, when combining these concepts, it would appear that HOI should be stronger because it has an extra oxygen. Why is this not the case? Thank you in advance:)

My brother just explained it. Basically, you look at the conjugate base. When you get the conjugate base of HOI, you get OI-. Because the oxygen has greater electronegativity than iodine, it will draw electrons towards itself rather than away. Therefore, there is less electron withdrawal away from oxygen. In HI, however, you have I- as the conjugate base, which is much stabler because it is bigger and therefore can accommodate more electrons (greater e- withdrawing power).