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Homework Help: Solving for pH with diprotic/triprotic acids

  1. Apr 20, 2006 #1


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    i know if you have an acid, say .0001 M HCl, to get the pH you simply take the -log of the acid concentration (which is the same as [H+]), but what if you have a diprotic (H2SO4) or triprotic (H3PO4) acid...do you need to multiply the acid contentration by 2 or 3 to get the new H+ concentration BEFORE plugging it into -log[H+]?

    and the same goes for pOH? eg. Mg(OH)2 needs to be multiplied by 2?
  2. jcsd
  3. Apr 20, 2006 #2


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    Homework Helper
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    Last edited by a moderator: May 2, 2017
  4. Apr 20, 2006 #3
    Mg(OH)2 do not completely ionise in water as do for instance NaOH or KOH.
  5. Apr 20, 2006 #4


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    Staff: Mentor

    Last edited by a moderator: Aug 13, 2013
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