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Homework Help: Formulas and Reactions

  1. Sep 11, 2007 #1
    1. The problem statement, all variables and given/known data

    How much weight would 5g of CuSO4 5H2O lose if ti were dried at 120 degrees C for 12 hours (i.e. if it were heated to drive off all the water of hydration)?

    3. The attempt at a solution

    CuSO4 = 159.61 g/mol
    H2O = 18 g/mol = 90 g for 5 mols

    159.61/(159.61 + 90) = 6.25%

    5 g * 6.25% = amount of CuSO4 = .313 g

    5 - .313 = how much H2O lost = 4.687 g

    but this isnt the correct answer.

    Any help would be greatly appreciated

  2. jcsd
  3. Sep 14, 2007 #2
    Find how many moles of CuSO4*5H2O are in 5g of the hydrate and then multiply by the molar mass of the anhydrate.
  4. Sep 14, 2007 #3


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    Gold Member

    I get 0.6394 for this expression. What does this value represent?
    Everything from here on is wrong because both the arithmetic and the logic is faulty.
    Find the formula weight of the pentahydrate. From that information, calculate the number of moles of the pentahydrate in 5 grams of the pentahydrate. This will equal the number of moles of the anhydride. You can do it from there...
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