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Homework Help: What is the percentage of ammonia in the sample?

  1. Jan 28, 2010 #1
    1. The problem statement, all variables and given/known data

    Ammoniacal nitrogen can be determined by treatment of the sample with chloroplatinic acid; the product is slightly soluble ammonium chloroplatinate: H2PtCl6 + 2NH4 --> (NH4)2PtCl6 + 2H

    The precipitate decomposes on ignition, yielding metallic platinum and gaseous products:
    (NH4)2PtCl6 --> Pt(s) + 2Cl2(g) + 2NH3(g) + 2HCl(g)

    Calculate the percentage of ammonia in a sample if 0.2115g gave rise to 0.4693g of platinum.
    2. Relevant equations



    3. The attempt at a solution

    0.4693(1/(14+1+1+1))= 0.0276
    0.0276(2)(159)= 8.778
    8.778/0.2115= 41.5%

    did I do this right? The back of my chemistry book says that the answer should be 38.74% NH3, so if this is correct how would you arrive at this answer?
     
  2. jcsd
  3. Jan 29, 2010 #2

    Lok

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    Did you use NH4 or NH3 as ammonia is NH3. Might be a mistake there as for Molecular mass 17 the result is the one in the book.
     
  4. Jan 29, 2010 #3

    Borek

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    Staff: Mentor

    Please elaborate, I have no idea what you did. You started dividing mass of platinum by the molar mass of ammonia, next you multiplied the result by 2 (stoichiometric coeffcient) and by molar mass of platinum (with digits reversed to make it harder to guess what you did). From what I understand at this stage your result is in rather unexpected units:

    [tex]\frac {(g_{Pt})^2 (mol_{NH_3})^2} {g_{NH_3} (mol_{Pt})^2}[/tex]

    I doubt that's what you wanted to do, from the last operation seems like you think at this stage you have mass of ammonia multiplied by 100.

    Book answer is correct.
     
    Last edited by a moderator: Aug 13, 2013
  5. Jan 29, 2010 #4

    Lok

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    Btw. With 18 I get the same wrong result as you. The things you wrote here make sense but weird that you don't get the result.
     
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