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Acidity of oxoacids of P

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Homework Statement



What is the order of acidity of H3PO3, H3PO2 and H3PO4?


The Attempt at a Solution



H3PO4 must be most acidic because its basicity is highest. Greater the no. of repleacable H+, greater will be its acidity. On similar reasoning, H3PO2 is least acidic.

Is it right?
 

Answers and Replies

  • #2
Borek
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There is a rule about acid strength and amount of oxygen in the molecule.
 
  • #3
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I guess you are talking about the withdrawing effect of Oxygens.
There is only one Oxygen doubly bonded to Phosphorus which withdraws electron density of the O-H group facilitating the release of H+. Since there is only one such O in every molecule given, I don't think we can compare based on that rule. Correct me if I am wrong.
 
Last edited:
  • #4
Borek
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Good point, my mistake.

Safest approach it to check tables for Ka values.
 
  • #5
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I googled their Ka values and to my surprise, found that the acidity order is opposite to that I mentioned in O.P.

Unfortunately these values are not given in my exam and I need an answer theoretically ( I am not so good at by-hearting things :biggrin:)
 

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