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Homework Help: I keep getting errors in a simple copper sulfate experiment

  1. Oct 2, 2008 #1
    1. The problem statement, all variables and given/known data

    I need to find the total number of water molecules per copper sulfate molecule. The answer is 5. But, I keep getting ~4 with the average of two dehydrating experiments.

    2. Relevant equations with my Attempts

    I am just using simple factor equations for these. I am converting from the weight of water that I liberated to moles. Then, comparing moles to find experimental values for the number of water molecules in the copper sulfate. I hope you understand. This is the first time I've tried to use LateX

    Test 1

    0.340g H2O * [tex]\frac{1 mol H_{2}O}{18.016g H_{2}O}[/tex] = 0.0189 mol H2O

    0.6449g CuSO4 * [tex]\frac{1 mol CuSO_{4}}{159.62g CuSO_{4}}[/tex] = 0.00404 mol CuSO4

    Experimental number of H2O Molecules is 4.68 or [tex]\frac{0.0189 mol H_{2}O}{0.00404}[/tex]

    That's fine for that one, I can round up to 5 for the ratio.

    For the second test, I used the same equations with the measured weight of 0.328g H2O and 0.729g CuSO4.

    This gives 0.0182 mol H2O and 0.00457 mol CuSO4.

    The experimental value for the number of H2O molecules comes out to 3.98.

    This is where I am not doing so well (obviously). When I average these two and round off, I get 4. To the best of my knowledge, copper sulfate tetrahydrate doesn't exist.

    So, am I just dealing with imperfect lab situations (technique, materials, etc..), or is there a fundamental flaw in my approach. Thanks for your time.

  2. jcsd
  3. Oct 4, 2008 #2


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    It's the former.
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