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17 August, 00:37

A sample of hydrated magnesium sulfate (MgSO4)

has a mass of 12.845 g. When it is dehydrated,

the anhydrous sample has a mass of 6.273 g.

Which is the correct chemical formula for the

hydrate?

+3
Answers (1)
  1. 17 August, 02:03
    0
    MgSO4.7H2O

    Explanation:

    Let the formula for the hydrated magnesium sulphate be MgSO4. xH2O

    Mass of the hydrated salt (MgSO4. xH2O) = 12.845g

    Mass of anhydrous salt (MgSO4) = 6.273g

    Mass of water molecule (xH2O) = Mass of the hydrated salt - Mass of anhydrous salt = 12.845 - 6.273 = 6.572g

    Now, we can obtain the number of mole of water molecule present in the hydrated salt as follows:

    Molar Mass of hydrated salt (MgSO4. xH2O) = 24 + 32 + (16x4) + x (2 + 16) = 24 + 32 + 64 + x (18) = 120 + 18x

    Mass of xH2O / Molar Mass of MgSO4. xH2O = Mass of water / mass of hydrated salt

    18x/120 + 18x = 6.572/12.845

    Cross multiply to express in linear form

    18x x 12.845 = 6.572 (120 + 18x)

    231.21x = 788.64 + 118.296x

    Collect like terms

    231.21x - 118.296x = 788.64

    112.914x = 788.64

    Divide both side by 112.914

    x = 788.64 / 112.914

    x = 7

    Therefore the formula for the hydrated salt (MgSO4. xH2O) is MgSO4.7H2O
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