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Homework Help: Ksp Calculation

  1. Nov 13, 2011 #1
    1. The problem statement, all variables and given/known data


    I need to calculate the Ksp of Ag2CrO4 based on experimental data.

    During the experiment, 1.25g of pure copper was placed in a 1.00 L solution of silver chromate. When the copper was extracted, only 1.24g remained.
    Balanced chemical equation: Cu + Ag2CrO4 --> CuCrO4 + 2Ag

    3. The attempt at a solution

    Here's what I did:

    mole of copper = 0.01g / 63.546
    = 1.57 * 10^-4

    Since volume is 1.00 L, the number of moles is equal to the concentration.
    There are 2 moles of Ag and 1 mole of CrO4 for every mole of copper, so:

    Ksp = (1.57 * 10^-4) (3.15 * 10^-4) (3.15 * 10^-4)
    = 1.56 * 10^-11

    But this doesn't seem correct because the actual value is 1.1 * 10^-12.
    This would give me a percentage error of over 1000%...

    Any help would be much appreciated.
  2. jcsd
  3. Nov 14, 2011 #2


    User Avatar

    Staff: Mentor

    Your approach looks correct and the answer seems to be consistent with the data given.

    I don't like this question. I wonder how they extracted the copper. Solid left after reaction completed should weigh more, not less.
  4. Nov 16, 2011 #3
    Ok, I thought I was doing it properly. I'm not sure why they made a question that produced a % error greater than 1000. Anyways, thanks Borek!
  5. Dec 3, 2012 #4
    I'm currently working on this same question, lol, can you tell me if the answer to this question was marked correctly? I got the same answers with the same approach.. I know this thread is a year old ._.
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