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Boedecjt01 Boedecjt01
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3 years ago
1) A student collects the following data in order to find the chemical formula of a Copper sulfate hydrate.  A 1.104 gram sample of unknown hydrate loses 0.3983 grams of water when heated.  Reaction with aluminum produces 0.2810 grams of copper metal. The remaining mass must have been sulfate ion (SO4-2).  Find the moles of water, the moles of copper and the moles of sulfate ion in the sample. Then give the chemical formula for the copper sulfate hydrate.
       I know that a mole is 6.022 x10^23, but I'm not sure how to calculate the above questions.

2) Assuming the unknown hydrate in problem #1 was weighed using a balance
    that is accurate to the nearest milligram (± 0.001 grams), what is the percent random error for that measurement?
       
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Laser_3Laser_3
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3 years ago
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Hi,

6.022*10^23 is Avogadro number which is a conversion between moles and molecule/atom. You will not use that in this problem. You would need molar mass to go from mass (grams) to moles.

mass of water: 0.3983g                                moles of water: 0.3983/18.02 = .0221
mass of copper: 0.2810g                                moles of copper: .2810/63.546 = .00442
mass of sulfate ion:   1.104 - 0.3983 - 0.2810 = 0.42      moles of sulfate ion: .42/96.06  = .00442

ratio of moles of water and copper: .0221/.004422 = 5
Chemical formula for copper sulfate hydrate: CuSO4*5H2O

2) percent random error = (.001/1.104) *100 = .09%

Hope this helps,
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