Acid strength

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Clara Cho 2K
Posts: 103
Joined: Wed Sep 18, 2019 12:18 am

Acid strength

Postby Clara Cho 2K » Mon Dec 02, 2019 11:27 am

Why is HI a stronger acid than HF?

Brian Tangsombatvisit 1C
Posts: 119
Joined: Sat Aug 17, 2019 12:15 am

Re: Acid strength

Postby Brian Tangsombatvisit 1C » Mon Dec 02, 2019 11:28 am

For HI, Iodine is a much larger and less electronegative atom than Fluorine, so it exerts a much weaker pull on H+. As a result, HI has a weaker bond, allowing it to dissociate to a much greater extent than HF. Since the strength of an acid is directly proportional to how much it is able to dissociate, HI is a stronger acid than HF.

Jessica Li 4F
Posts: 115
Joined: Fri Aug 09, 2019 12:16 am

Re: Acid strength

Postby Jessica Li 4F » Mon Dec 02, 2019 11:56 am

Since the F atom in HF pulls the H so strongly, it's hard for the H to "escape" and break the bond between them two to result in their respective ions.

In addition, the trend goes that HF < HCl < HBr < HI in terms of acid strength because the bond strengths (and lengths) are increasingly weaker.

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