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20 July, 12:58

You are given a 2.9237 g sample of a substance with the generic formula MCl2 (H2O) 6. After completely drying the sample (which means removing the 6 moles of H2O per mole of MCl2), the sample weighs 1.5941 g. What is the identity of element M? Write your answer as a chemical symbol.

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  1. 20 July, 13:20
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    M is cobalt (Co)

    Explanation:

    Step 1: Data given

    Mass of MCl2 (H2O) 6 = 2.9237 grams

    After completely drying the sample (which means removing the 6 moles of H2O per mole of MCl2), the sample weighs 1.5941 g.

    Step 2: Calculate mass of water

    Mass of water = 2.9237 - 1.5941 = 1.3296 grams

    Step 3: Calculate moles water

    Moles water = mass water / molar mass water

    Moles water = 1.3296 grams / 18.02 g/mol

    Moles water = 0.07378 moles

    Step 4: Calculate moles of the whole substance

    For 1 mol MCl2 (H2O) 6 we have 6 moles H2O

    Number of moles of the whole substance = 0.07378 / 6 = 0.01230 moles

    Step 5: Calculate molar weight of the substance

    Molar weight = mass / moles

    Molar weight = 1.5941 grams / 0.01230 moles

    Molar weight = 129.6 g/mol

    Step 6: Calculate molar weight of M

    Molecular weight of M = 129.6 - (2*35.45)

    Molecular weight of M = 58.7 g/mol

    M is cobalt (Co)
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