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22 September, 15:21

0.070g of hydride of carbon occupies 56cm^3 at S. T. P when vaporized and contained 14.29% by mass of hydrogen. What is the formula for the hydrocarbon

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  1. 22 September, 17:16
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    C₂H₄

    Step-by-step explanation:

    Assume that you have 100 g of the compound.

    Then you have 85.71 g of C and 14.29 g of H.

    1. Calculate the moles of each element.

    Moles of C = 85.71 * 1/12.01 = 7.130 mol C

    Moles of H = 14.29 * 1/1.008 = 14.18 mol H

    2. Calculate the molar ratios.

    Divide all values by the smallest number.

    C: 7.130/7.130 = 1

    H: 14.18/7.130 = 1.986

    3. Determine the empirical formula

    Round off all numbers to the closest integer.

    C: 1

    H: 2

    The empirical formula (EF) is CH₂.

    4. Calculate the EF mass

    EF Mass = (12.01 + 2.016) u

    EF Mass = 14.03 u

    5. Calculate the moles of compound

    STP is 0 °C and 1 bar.

    1 mol of a gas occupies 22.71 dm³ at STP.

    56 cm³ = 0.056 dm³ Convert to moles

    = 0.056 * 1/22.71

    = 2.47 * 10⁻³ mol

    6. Calculate the molar mass

    MM = mass/moles

    = 0.070 g/2.47 * 10⁻³ mol

    = 28.39 g/mol

    7. Calculate the molecular formula (MF)

    The molecular formula is an integral multiple of the empirical formula.

    MF = (EF) ₙ

    n = MF Mass/EF Mass

    = 28.39 u/14.03 u

    = 2.023

    ≈ 2

    MF = (CH₂) ₂

    = C₂H₄

    The molecular formula is C₂H₄.
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