Why is HClO4 stronger than H3PO4?

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Anish Patel 4B
Posts: 59
Joined: Thu Jul 11, 2019 12:17 am

Why is HClO4 stronger than H3PO4?

Postby Anish Patel 4B » Tue Dec 03, 2019 12:40 pm

Since H3PO4 is polyprotic, shouldn't it be a stronger acid than HClO4 despite Cl's electronegativity?

Kishan Shah 2G
Posts: 132
Joined: Thu Jul 11, 2019 12:15 am

Re: Why is HClO4 stronger than H3PO4?

Postby Kishan Shah 2G » Tue Dec 03, 2019 12:42 pm

Because the conjugate base of HClO4, which is ClO4 is more stable than the conjugate base of H3PO4, so HClO4 is more likely to disassociate more in solution as H+ ions and ClO4- anions. Eventhough it is polyprotic, to my knowledge it really has no effect on acidity strength.

Here is a formal explanation by lavelle: viewtopic.php?t=8596

605208780
Posts: 50
Joined: Wed Sep 18, 2019 12:16 am

Re: Why is HClO4 stronger than H3PO4?

Postby 605208780 » Tue Dec 03, 2019 12:57 pm

Chlorine has a higher electronegativity than phosphorus, so it pulls the oxygen atom electrons towards itself with greater force than phosphorus. The fact that chlorine has a higher pull means that oxygen electrons become less accessible for the hydrogen atoms to "share", making it less favorable for hydrogen to stay bonded versus dissociating from the acid. Phosphorus by contrast pulls the electrons less, meaning that hydrogen has greater access to oxygen electrons, making it less favorable for it to dissociate

BritneyP- 2c
Posts: 101
Joined: Sat Sep 14, 2019 12:15 am

Re: Why is HClO4 stronger than H3PO4?

Postby BritneyP- 2c » Tue Dec 03, 2019 1:51 pm

HClO4 is stronger because Cl has a higher electronegativity than P and so the oxide is overall more stable. As a result of its stability, it is more acidic than H3PO4


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