determining the strongest acid

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Nawaphan Watanasirisuk 3B
Posts: 58
Joined: Tue Nov 28, 2017 3:03 am

determining the strongest acid

Postby Nawaphan Watanasirisuk 3B » Fri Dec 07, 2018 10:52 am

We learned 2 rules that tell us an acid is strong— 1. Weaker [longer] bonds = stronger acid because loses H+ easier
2. Resulting anion must be stable i.e. resonance or high electronegativity pulls the - charge to it and away from H+.

How do we know which rule to to apply if an acid have a stronger bond but resulting anion is more stable.

For example ClO, BrO, IO.

IO has the longest bond because iodine, but Cl is more electronegative and therefore stabilizes the anion when it loses the H+.

The answer is ClO is a stronger acid but how do we know which rule to use when they contrast like this?

mahika_nayak_3L
Posts: 60
Joined: Fri Sep 28, 2018 12:26 am

Re: determining the strongest acid

Postby mahika_nayak_3L » Fri Dec 07, 2018 2:20 pm

For oxoacids, the textbook lists 2 rules. Firstly, if the oxoacids have the same central atom, then the oxoacid with the greater number of oxygens will be a stronger acid because the conjugate base is more stable. Secondly, if the # of oxygens is the same, the oxoacid with the more electronegative central atom will be stronger. This is because, in oxoacids, the H does not bond to the central atom but instead to the O. The more electronegative atom will draw the electron density away from the O-H bond, thus making it easier for this molecule to donate its H and making it a stronger acid. For this reason, because the "Cl" in HClO is more electronegative than the "I" in HIO, HClO is the stronger acid.

Kassidy Tran 1E
Posts: 77
Joined: Fri Sep 28, 2018 12:15 am

Re: determining the strongest acid

Postby Kassidy Tran 1E » Fri Dec 07, 2018 2:26 pm

Using these rules, does that mean that BrO is a stronger acid than IO as well?


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