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Question on Selective precipitation

  1. Oct 17, 2007 #1
    can any one check if this is right?

    question :
    Explain if a solution contains both I− and Cl− at about 0.01 M, can we determine the amount of Cl− and I− independently by using gravimetric analysis?

    yes
    add [AG+] to precipitate out the I- first ( ksp is smaller)

    0.01M * (0.01%/100%) = 1.0E-6 M I-
    ksp = [Ag+][I-]
    8.5E-17 = [Ag+](1.0E-6)
    [Ag+] = 8.5E-11 M <------ add to precipitate AgI

    increase [Ag+] to precipitate Cl- left
     
  2. jcsd
  3. Oct 17, 2007 #2

    Gokul43201

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    Why are you multiplying the molarity by (0.01%/100%) ?
     
  4. Oct 17, 2007 #3
    to lower the concentration:

    i found using google:
    "What do we mean by complete separation--> the concentration in solution of the analyte of interest must be less than or equal to 0.01% of its original value."
     
  5. Oct 17, 2007 #4

    Gokul43201

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    Okay, so you want to remove 99.99% of I-. That's fine. You've calculated that it takes 8.5E-11M of Ag+ to precipitate most of the I-.

    So far, so good. Now what do you need to calculate next?
     
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