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22 March, 12:36

A certain alcohol contains only carbon, oxygen and hydrogen. When 50

grams are combusted in air, 26.05 grams of C and 6.630 grams of H20 are

produced. If the molecular mass of this alcohol is 189 amu, what is its

molecular formula?

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Answers (1)
  1. 22 March, 14:58
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    C12H208 is the molecular formula of the alcohol.

    Explanation:

    The weight of carbon given is 26.05 grams

    The weight of H20 = 6.630 grams

    first let us find the number of moles of:

    number of moles = weight given : mass of 1 mole of the element

    = 26.05 : 12

    = 2.170 moles of carbon

    number of moles of hydrogen present in H2O

    = 6.630 : 18

    = 0.368

    1 mole of water contains 2 mole of hydrogen so, 2 * 0.368 grams

    = 0.7366 moles

    Number of moles of oxygen cannot be calculated as of now.

    So from the data obtained,

    50 gms C2H2Ox is combusted.

    Lets, calculate the gms from moles using the same equation

    For carbon, 2.170 * 12

    = 26.04 grams

    For hydrogen, 0.368 * 1.01

    = 0.3716 grams

    adding the carbon and hydrogen content, 26.04 grams

    now the oxygen content can be obtained by

    50 - 26.04

    = 23.96 grams

    Now moles of oxygen calculated as

    n = 23.96 : 16

    = 1.49 moles of oxygen

    The emperical formula for the alcohol is C6H04

    now the molar mass is divided by emperial formula mass.

    molar mass = 189 amu

    emperial formula mass = 137

    the division would give = 1.37

    it can be taken as 2

    The subscript in the formula is multiplied by 2 to get molecular formula from emperial formula.

    So, C12H208 is the molecular formula of the alcohol.
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