怡妏 asked in 科學化學 · 1 decade ago

利用氣體密度計算得知氣體分子式

What us the molar mass of a gaseous alkane hydrocarbon having a density of 2.42 g/L at 20℃ and 762 Torr?

What is the molecular formula of the gas?

1 Answer

Rating
  • 1 decade ago
    Favorite Answer

    According to the theory of ideal gas, the volume of one mole gas under standard conditions (0 degree C and 1 atm) should be 22.4L. If the temperature is raised to 20 degree C, the volume of the gas (Vt) will be expanded.

    Vt = Vo*[1 (t/273)]

    Vt = 22.4 L*[1 (20/273)]

    Vt = 24.04 L (<-- the gas volume at 20 degree C and 760 torr)

    However, if the pressure of the gas is raised, the volume of the gas will be reduced. (Note: 1 atm = 760 torr)

    P1V1 = P2V2

    1 atm*24.04 = (762/760)*V2

    V2 = 23.98 L (<--the gas volume at 762 torr and 20 degree C)

    Therefore, the molar mass of the gas you indicated will be:

    Molar mass = 2.42 g/L * 23.98 L = 58.02 g (for the FIRST ANSWER)

    The molecular formula of the gass should be CnH2n 2

    Therefore, 12*n 1*(2n 2) = 58.02

    14*n 2 = 58.02

    n = 4

    The molecular formula of the gas should be C4H10 (for the SECOND ANSWER)

    2008-10-29 20:28:37 補充:

    A minor correction for the part of the second answer:

    The molecular formula of the gass should be CnH2n + 2

    Therefore, 12*n + 1*(2n + 2) = 58.02

    14*n 2 = 58.02

    n = 4

    The molecular formula of the gas should be C4H10 (for the SECOND ANSWER)

Still have questions? Get your answers by asking now.