CHEM

I don't understand how to find the formula of a hydrate. Here's one of the question. if you guide me through it I think I'll be able to do the rest of them. Thanks :)

When 100g of ZnSO4x�œH2O is heated, 43.86g of water is given off. Calculate the formula of the hydrate.

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asked by Lena
  1. ZnSO4xH20 �¨ ZnSO4 + xH2O

    No. of moles of H2O = mass �€ molar mass
    = 43.86 �€ 18
    = 2.4367 mols

    No. of moles of ZnSO4xH20
    = mass �€ molar mass
    = 100 �€ (161 + 18x) mols
    No. of moles of ZnSO4xH20
    = 1/x X no. of moles of H2O
    = 1/x X 2.4367
    = i.e. 2.4367/x mols
    Therefore, 2.4367/x = 100 �€ (161 + 18x)

    Solving the equation,
    100x = 2.4367 (161+18x)
    56.1394x = 392.3087
    x = 6.990
    = 7 (whole no.)
    Hence the formula is ZnSO4. 7H2O
    There are 7 water molecules.

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    posted by Jen
  2. Please note that those missing symbols mean divide. i.e.
    no. of moles = mass/molar mass

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    posted by Jen

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