Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: atbear on 23/08/2003 09:45:29
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I have a bet with my cousin.... we were talking about HF, and he said that HF is the strongest acid (assuming that from it's electronegativity), and I told him no, that it's sooo electronegative that it holds on to the Hydrogen too well and that it was actually a weak acid.... Well we got all wound up about it, because he didn't believe me. He also insists that HF is the most reactive acid (I questioned this) but I didn't tell him definately no.
So my questions are in regard to HCl and HF (I used HCl my strong acid example):
1. What is the stronger acid, HF or HCl?
2. What is the more reactive acid, HF or HCl?
3. Why for both (if you don't mind telling)?
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An acid is also called a proton donor. So a strong acid means it donates H+ readily. I agree with you that HCl is stronger than HF as fluorine attracts the hydrogen so strongly. I'm not sure which one is more reactive.
Angel (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fsmilies.networkessence.net%2Fs%2Fcontrib%2Fruinkai%2FbiggrinangelA.gif&hash=7a3ab31861328a98db23edcb21639ab9)
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Acids which are considered "strong acids" are classified only as a function of thier ability to completely dissociate in water. It has nothing to do with their ability to donate a proton. Any acid which does not completely ionize in water is considered a weak acid, no matter how corrosive it may be.
HF, while it is extraordinarily reactive, is not a strong acid because it does not obtain 100% ionization into H+ and F- in aqueous solution.
The only strong acids are: HCl, HI, HBr, HNO3, HClO3, HClO4, and H2SO4. (note that only one proton of H2SO4 dissociates completely...the resulting ion HSO4- is only weakly acid)
In more mathematical terms...if you place any of the strong acids into aqueous solution, for every mole of the acid you'll receive a mole of H+. For weak acids, you'll receive a smaller amount based on the ionization constant for that acid. (pKa)
So, you are correct in your statement to your cousin...HF is a weak acid, but not exactly for the reason you thought.
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Nicely explained. Thanks.
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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deleted as inapproprate