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26 May, 13:20

A sample of 2.0 moles of a metal reacts completely with excess oxygen to form 62.0 g of M2O. What element is represented by the symbol M?

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  1. 26 May, 14:27
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    1) State the chemical reaction

    4M + O2 - - - > 2M2O

    2) State the molar ratios

    4 mol M : 1 mol O2 : 2 mol M2O

    3) Calculate the number of moles of M2O produced

    4 mol M / 2 mol M2O = 2 mol M / x = > x = 2 mol M * 2 mol M2O / 4 mol M

    => x = 1 mol M2O

    4) Calculate the molar mass of M2O

    molar mass = mass in grams / number of moles = 62.0 g / 1 mol = 62.0 g/mol

    5) Calculate the atomic mass of M

    molar mass of M2O = 2 * atomic mass of M + atomic mass of O = >

    62.0 = 2 * atomic mass of M + 16

    => atomic mass of M = [62.0 - 16] / 2 = 23

    6) Compare that atomic mass with the atomic masses of the metals in the periodic table.

    You will find that 23 is the atomic mass of sodium.

    Answer: sodium
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