Elemental Composition of Pure Substances

AP Chemistry· difficulty 1/5

A 0.250 g sample of a hydrocarbon is burned completely in excess O2. The combustion products are passed through a dehydrating tube (gains 0.306 g) followed by a CO2 absorber (gains 0.747 g). The hydrocarbon contains only C and H.

A separate measurement gives a molar mass of 84 g/mol. What is the molecular formula?

  • A

    C5H10

  • B

    C7H14

  • C

    C6H12

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  • D

    CH2

Explanation

Empirical mass = 14 g/mol. 84/14 = 6 -> C6H12.

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