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gchem solution problem

Discussion in 'DAT Discussions' started by andyjl, Apr 27, 2007.

  1. andyjl

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    What is the normality of a 1M solution of H3PO4 titrated with CaCl2?

    Ans: 1.5

    Someone please explain
     
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  3. poc91nc

    poc91nc Banned
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    2PO43- + 3Ca2+ ----> Ca3(PO4)2

    Calcium phosphate is insoluble by the way

    1mol of phosphate reacts with 3/2 mol equiv. of Ca2+

    N = 1(1.5) = 1.5
     
  4. andyjl

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    How do you know how to set up the equation that way and to ignore the other product HCl?
     
  5. poc91nc

    poc91nc Banned
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    HCl will dissociate immediately...furthermore...chloride salts are soluble except for with Hg2 ++, Ag+, Pb++, Cu+...when you set up the equation you have to eliminate spectator ions. therefore...know the solubility rules...


    However...the answer 1.5 assumes complete dissociation of H3PO4...don't really think of H3PO4 dissociating completely in Calcium Chloride

    Here is another way to think of normailty

    H3PO4 titrated with NaOH

    1mol H3PO4 reacts with 3equiv NaOH/mol H3PO4
     
  6. poc91nc

    poc91nc Banned
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    Does the problem mention anything about being titrated in basic solution?
     
  7. andyjl

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    No, that was it.
     
  8. PD3

    PD3

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    Could you write out the steps in finding the final equation
     
  9. poc91nc

    poc91nc Banned
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    With normality questions....just make sure you know the definition of normality.

    N = mol x equiv/mol

    Most of our study guides use normality for acid base titrations only and a chemical equation is not needed...

    But for redox titrations...the equation is needed...look in your chemistry textbook for redox titration problems
     

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