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Stoichiometry question

  1. Oct 11, 2012 #1
    1. The problem statement, all variables and given/known data

    given that 40.14g sample of hydrated NiSO4 is reduced in mass to 22.14g upon heating.
    Show that the formula of the hydrate is NiSO4.7H20

    2. Relevant equations

    n / M

    3. The attempt at a solution

    22.14g/ 40.14g = 0.5516 (mol of NiSO4)

    40.14g - 22.14 = (18 g H20 lost in heating)

    18.0 / 18.02 = 0.9989 (mol of H20)

    ∴ mole ratio = 0.5516 : 0.9989

    but this does not give the result in the ratios of 1:7 (NiSO4.7H20)


    stoichiometry (or chem for that matter) isn't really my thing and I have about 10 questions similar to this, can someone please point me in the right direction please?
     
  2. jcsd
  3. Oct 11, 2012 #2
    22.14/ 150.76 = 0.1469 (mols of NiSO4)

    0.1469:0.9989
    1.469:9.989 (x10)

    which is a ratio of 1:6.79

    but is there a more accurate way of calculating this?
     
  4. Oct 11, 2012 #3
    Your second calculation is much better than the first. Have another try at calculating the molar mass of NiSO4. 150.76 g/mol is wrong.
     
  5. Oct 11, 2012 #4
    thanks for the tip johnRC, I needed to check my copy of the periodic table better!

    does this calculation look more correct? the ratios are almost perfect, which my chem teacher has said is to be expected.

    22.14 / 154.76 = 0.14306 (mols of NiSO4)
    40.14g - 22.14 = 18.00 (H20 lost in heating)
    18.0 / 18.02 = 0.9989 (mols of H20)
    0.14306:0.9989
    0.14306/0.9989 = 0.1432
    1/0.1432 = 6.982

    1:6.982
    6.98 ≈ 7
    ∴ NiSO4.7H2O
     
  6. Oct 11, 2012 #5
    Right on, symmetrica1!
     
  7. Oct 12, 2012 #6
    thanks john!

    could anyone take a look at this for me please?

    Given that a 139.4g sample of hydrated MnSO4 is reduced in mass to 94.38g upon heating, find the empirical formula of the Hydrate. Also, write the name of the hydrate of manganese sulphate.

    94.38g / 151g = 0.6250 (mols of MnSO4)
    139.4g – 94.38g = 45.02g (H2O lost in heating)
    45.02 / 18.02 = 2.4983 (mols of H2O)

    0.6250:2.4983
    0.6250/2.4983 = 0.250166
    1 / 0.250166 = 3.997

    1:3.997
    3.997 ≈ 4
    ∴ MnSO4.4H2O

    would the name of the hydrate be Manganese (II) sulfate monohydrate?
     
    Last edited: Oct 12, 2012
  8. Oct 12, 2012 #7

    Borek

    User Avatar

    Staff: Mentor

    Yes.

    No.

    Mono means one, not four.

    Please start new threads if you have new questions.
     
  9. Oct 12, 2012 #8
    sorry borek, I thought it would come under the same topic heading anyway so was just trying to keep your forums neat. Will do in future posts

    thanks for checking my answer
     
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