How do you find the value for pKa3 for phosphoric acid?

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How do you find the value for pKa3 for phosphoric acid?

Postby Chem_Mod » Sun Aug 21, 2011 12:16 pm

How do you find the value for pKa3 for phosphoric acid?

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Re: How do you find the value for pKa3 for phosphoric acid?

Postby Chem_Mod » Sun Aug 21, 2011 12:16 pm

Remember that phosphoric acid is a triprotic acid (H3PO4). Ka1 refers to the reaction that removes the first hydrogen: H3PO4 + H2O <-> H2PO4- + H3O+. Ka2 refers to the reaction that removes the second hydrogen: H2PO4- + H2O <-> HPO4-2 + H3O+. Ka3 refers to removing the last hydrogen: HPO4-2 + H2O <-> PO4-3 + H3O+. For Ka3, we are interested in HPO4-2 and PO4-3. For Ka2, we are interested in HPO4-2 and H2PO4-.


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