What is meant by the symbol K_a3 for H3PO4?

Chemistry HW question

4 Answers

  • Gianni
    Lv 7
    8 years ago
    Favorite Answer

    Orthophosphoric acid is a triprotic acid , weak in all three dissociations. So you have 3 equilibrium dissociation:

    H3PO4 + H2O <------> H2PO4(-) + H3O(+)

    H2PO4(-) + H2O <------> HPO4(2-) + H3O(+)

    HPO4(2-) + H2O <------> PO4(3-) + H3O(+)

    with relative dissociation constants:

    Ka1 = [H2PO4-] * [H3O+] / [H3PO4]

    Ka2 = [HPO4(2-)] * [H3O+] / [H2PO4-]

    Ka3 = [PO4(3-)] * [H3O+] / [HPO4(2-)]

    Bye Bye :)

  • 8 years ago

    Ka1 is for removing one H from H3PO4 and getting the H2PO4^-2 ion

    Ka2 is for removing one H from the H2PO4^-2 ion and getting the HPO4^-2 ion

    Ka3 is for removing one H from the HPO4^-2 ion and getting the PO4^-3 ion

    Ka1 is always bigger than Ka2 which is always bigger than Ka3

  • 8 years ago

    dissociation constant for an acid

    H3PO4 dissociates into H+ and PO4 3-

  • Anonymous
    6 years ago


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