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The normality of 0.3 M phosphorus acid (H3PO3) is.......

  • Chemistry -

    Normality is Molar concentration divided by an equivalence factor. (n = c/f)

    The hydrogen equivalence factor of an acid is the number of moles of acid that contains 1 mole of acidic hydrogen atoms.

    The hydrogen equivalence factor of a triprotic acid is 1/3, so the normality of a triprotic acid is 3 times its molar concentration.

    So for phosphorus acid: 0.3M = 0.9N

    Any confusion felt during the reading of this explanation is one of the reasons the use of normality is depreciated in chemistry.

    (Unfortunately it is still sometimes used in medicine.)

  • Chemistry -


  • Chemistry-doh. -

    Doh! Right.

    H3PO3 is diprotic, not triprotic like H3PO4.

  • Chemistry -

    I most certainly disagree with any statement that normality is not needed anymore although I agree it is confusing (sometimes) and its use has been discouraged since the IUPAC and a lot of smarter people than I am changed all the rules. (Yes, you hit a sore spot. I wish we still had normality.)
    Second, I would like to point out to Aman that technically the question posed can't be answered without knowing the equation. Note that
    H3PO3 + NaOH ==> NaH2PO3 + H2O and the factor is molar mass H3PO3/1 but for

    H3PO3 + 2NaOH ==> Na2HPO3 + 2H2O the factor is molar mass H3PO3/2. That is the equivalent weight of a substance is the molar mass divided by the number of REPLACED H ions. Therefore, an acid like H3PO4 may have three different equivalent weights depending upon how many H ions are actually displaced in a reaction.

  • Chemistry -

    Chemistry sucks

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