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Thread: ACID + BASE equations...and H+ concentrations.

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    ACID + BASE equations...and H+ concentrations.

    Equal volumes of equimolar solutions:
    H3PO4 + NaOH --> NaH2PO4(aq) + H2O

    As the relative amount of OH- increases, you could get
    H3PO4 + 2NaOH --> Na2HPO4(aq) + 2H2O

    And with a substantial excess of NaOH, then you get
    H3PO4 + 3NaOH --> Na3PO4(aq) + 3H2O

    Do we need to know all three? Or just the last one.


    Also, for monoprotic acids (like HCL), the concentration of it is the same as the H+ concentrations.
    If you had a triprotic acid (like H3PO4), at concentration 0.1 mol/L, how do I find the H+ concetration? Is it possible?

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    Re: ACID + BASE equations...and H+ concentrations.

    Quote Originally Posted by Mr_Kap View Post
    Equal volumes of equimolar solutions:
    H3PO4 + NaOH --> NaH2PO4(aq) + H2O

    As the relative amount of OH- increases, you could get
    H3PO4 + 2NaOH --> Na2HPO4(aq) + 2H2O

    And with a substantial excess of NaOH, then you get
    H3PO4 + 3NaOH --> Na3PO4(aq) + 3H2O

    Do we need to know all three? Or just the last one.


    Also, for monoprotic acids (like HCL), the concentration of it is the same as the H+ concentrations.
    If you had a triprotic acid (like H3PO4), at concentration 0.1 mol/L, how do I find the H+ concetration? Is it possible?
    For HSC, you don't need to calculate numerical values for polyprotic acids, since the latter stages don't dissociate 100%. For things like H2SO4 (diprotic), if they do ask you to calculate, you'd just assume that 2 H+ ions result from each H2SO4 molecule (even though in reality it's something like 1.8).

    And if you have a good memory, best to memorise all the equations. I can't remember whether they are all needed or not.
    Mr_Kap likes this.

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    Re: ACID + BASE equations...and H+ concentrations.

    Quote Originally Posted by InteGrand View Post
    For HSC, you don't need to calculate numerical values for polyprotic acids, since the latter stages don't dissociate 100%. For things like H2SO4 (diprotic), if they do ask you to calculate, you'd just assume that 2 H+ ions result from each H2SO4 molecule (even though in reality it's something like 1.8).

    And if you have a good memory, best to memorise all the equations. I can't remember whether they are all needed or not.
    Ok. Thx.

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    Re: ACID + BASE equations...and H+ concentrations.

    Polyprotic acid equations also apply to buffer solutions (9.2.4.2.9). Blood contains three buffers (bicarbonate, hydrogen phosphate and haemoglobin). The bicarbonate buffer being the most important. I would suggest learning all of the equations associate with the CO2 / bicarbonate buffer, and also learning the three equations for the phosphate.

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