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8 May, 13:20

Use the data table to answer the questions below Mass of

evaporating dish ... 12.07g Mass of

evaporating dish plus hydrate ... 15.12 g Mass of

evaporating dish and anhydrous crystals ... 13.58g

If the hydrate used in the lab for the above data table is

MgSO4.7H20, then calculate the theoretical % water in the hydrate

15%

51%

73%

95%

100%

+3
Answers (1)
  1. 8 May, 17:17
    0
    Option B is correct : 51%

    Explanation:

    Data Given:

    Hydrates used in lab = MgSO₄.7H₂O

    % water in hydrate = ?

    Solution:

    As we look for the the theoretical % water in hydrates

    So

    First of all find the atomic masses of each component in a molecule

    For H₂O atomic masses are given below

    H = 1 g/mol

    O = 16 g/mol

    Then find the total mass of H₂O in hydrated salt

    7H₂O = 7 (2x1 + 1x16) g/mol

    7H₂O = 7 (2+16) g/mol

    7H₂O = 7 (18) g/mol

    7H₂O = 126 g/mol

    Now,

    > find total Molar Mass of Molecule:

    Molar Mass of MgSO₄ • 7H₂O = [24 + 32 + 16x4] + 7 (2+16)

    Molar Mass of MgSO₄ • 7H₂O = [24 + 32 + 64] + 126

    Molar Mass of MgSO₄ • 7H₂O = [120] + 126

    Molar Mass of MgSO₄ • 7H₂O = 246 g/mol

    Now to find the mass by percent of (water) H₂O

    Formula used to find the mass by percent of a component

    Percent composition of H₂O = mass of H₂O in Molecule / molar mass of MgSO₄•7H₂O x 100%

    Put the values in above formula

    Percent by mass of H₂O = 126 (g/mol) / 246 (g/mol) x 100%

    Percent by mass of H₂O = 0.51 x 100%

    Percent by mass of H₂O = 51%

    So,

    Option B is correct : 51%
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