Weak acid

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Miya Eberlein 1J
Posts: 29
Joined: Fri Sep 25, 2015 3:00 am

Weak acid

Postby Miya Eberlein 1J » Wed Dec 02, 2015 8:59 pm

Why does HF make a weak acid?

Preston Carroll 2F
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

Re: Weak acid

Postby Preston Carroll 2F » Wed Dec 02, 2015 9:33 pm

I'm assuming that you're confused as to why HF is a weak acid whereas all other H-Halogen (HCl, HBr, HI) compounds are strong acids. This has to do with the importance of size of the ion. F- is a relatively small ion in comparison to all other halogen ions, e.g., Cl-, Br-, and I-. You can also look at it in terms of the conjugate base. F- is very small ion and has less volume to spread its negative charge over, therefore it is a relatively strong conjugate base. A strong conjugate base implies a weak acid. Basically, this is an example of one of the times the periodic trends are broken because another rule takes precedence; HF is one to just to commit to memory as a weak acid.

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