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Homework Help: 11th gr. chem (composition of a hydrate)

  1. Oct 15, 2008 #1
    i might get confusing cause i dont understand this very much
    but here is the copy of my lab i need help with #1 & 6 of the POST-ALAYSIS
    here is the word doc. of my lab
    http://courses.digitaldapp.org/documents/Inquiry Lab - Experiment 03 - Composition of a Hydrate.doc

    5 grams of copper II sulfate was used
    when it became an anyhride it had a mass of 0.15g

    i know i made a mistake somewhere in my lab and i was wondering if you tell where my mistake is and what i should do. i would highly appreciate it.

    so i know...
    CuSO4 . 5H2O
    molar weight is 249.69g

    by itself is
    CuSO4 = 159.61g
    5H2O= 90.81

    so i took the
    mass of the water/total mass of hydrate x100= 36% of H2O removed in anhydrous copper (II) sulfate.

    am i correct?
    this is where i got confused...
    -determine the # of moles of water present in each mole of hydrous copper (II) sulfate.
    so what i did was:

    H10= 11%=11/1.0079=10.91=2
    is this the correct Empirical formula?
    2H10O5 & can be simplified to 2H2O

    so now what do i use to find the amount of moles of water present?
  2. jcsd
  3. Oct 17, 2008 #2


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    Gold Member

    Are you sure you got that right? I assume that "it had a mass of..." means that the anhydride had a mass of... Is that right?

    Good so far...

    Here is where you strayed off course. The formula for your unknown hydrate is CuSO4 . XH2O. You need to solve for 'X', not assume that it is 5 and do some math without using any of the data you collected.

    Show us the raw data you collected.
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