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Topic: Why are HBr and HI not superacids?  (Read 1754 times)

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Offline Toxic Frog

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Why are HBr and HI not superacids?
« on: March 29, 2014, 01:48:42 PM »
I'd like to start off by introducing myself. I've always been interested in all types of sciences but lately, I've taken an interest in chemistry. I graduate from high school in June and am looking into environmental science/conservation as a career. So since I required a couple of credits in chemistry, I signed up for some chemistry classes and have become interested in chemistry during the course of those classes (particularly with alkali and alkaline earth metals, metalloids, and halogens).

Anyhow, my first question is this. If superacids are defined as being stronger than concentrated sulfuric acid, why are hydrobromic acid and hydriodic acid not considered superacids? I've heard that HCl is marginally stronger than H2SO4, so why are HBr and HI, which are stronger than HCl, not considered to be superacids?

Also, why is it that hydrogen halides (except HF) are stronger than sulfuric acid, which is diprotic?

Offline kriggy

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Re: Why are HBr and HI not superacids?
« Reply #1 on: March 29, 2014, 03:24:18 PM »
I think its because the superacids are defined by hammett acidity function and the transition between superacid and normal acid is pure sulfuric acid with H0 of -12. THe thing is that in very concentrated solutions the things are different compared to diluted solutions, so if we are talking about aquaeos solutions, HCl, HBr etc. might be stronger than sulfuric acid, if we are talking pure acids, the things are different

Offline kahynickel

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Re: Why are HBr and HI not superacids?
« Reply #2 on: May 25, 2014, 01:52:09 PM »
As for acids and super acids one thing that you are missing here is the stability of conjugate base. you need to know what is a conjugate base, and the factors which affect its stability.

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