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Gravimetric Analysis- Questions

  1. Sep 23, 2005 #1
    Gravimetric Analysis-- Questions

    I am in first-year Chemistry in university and I can't seem to find the answers for two questions from my course work. I have tried many times, and I keep reading the textbook but I still can't get it.

    Please help if you know the correct answers. Thank you.

    Here are the questions:

    1.) A compound of Iron and Chlorine is soluble in water. An excess of Silver Nitrate was added to precipitate the chloride ion as silver chloride. If a 134.8 mg sample of the compound gave 304.8 mg of AgCl, what is the formula of the compound?

    2.) Determine the oxidation number of HgCr2O7.

    Thank you.
  2. jcsd
  3. Sep 23, 2005 #2

  4. Sep 24, 2005 #3
    I would appreciate if anyone could give me suggestions on these questions.
  5. Sep 25, 2005 #4
    1) First figure out the mass of the chloride ions. The compound is FeClx.

    304.8 mg AgCl --> 0.002 moles AgCl --> 0.002 moles Cl- --> 75 mg Cl-

    134.8 mg FeClx - 75 mg Cl- = 59.4 mg Fe+x

    0.002 moles Cl-
    59.4 mg Fe+x --> 0.001 moles Fe+x

    Therefore there is twice as much Cl- as Fe+x, so it must be Fe+2.


    This does not make sense. The problem is asking you for the oxidation of a certain atom or for the oxidations numbers of each atom.

    Since this is a compound you know that the overall charge is 0. The dichromate atom as an overall charge of -2. Oxygen is -2 in this case.
  6. Jul 30, 2010 #5
    Re: Gravimetric Analysis-- Questions

    2) HgCr2O7

    you will have to remember that Oxygen has an oxidation state of -2 no matter wat
    so, O7= -2*7 = -14

    as for Hg it will have an oxidation state of +2, because it is in the same group as zn.

    therefore -14+2= -12

    in closing Cr has an oxidation state of -12. but Cr2 will have to be -12/2 = -6. so since chromiun is beside oxygen its oxidation state changes to +6
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