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Chem questions about mole

發問:

a gaseous hydrocarbon contains 82.8% of carbon by mass 1. calculate the percentage by mass of hydrogen 2. find the empirical formula 3. if the density of the gas is 2.42g/dm^3 t r.t.p, calculate the molar mass fo this hydrocarbon 4.find the molecular formula of this hydrocarbon THANKS 更新: Can you tell me why you multiply 2.42 with 24? wat is 24? thx i m going to award u the best ans

最佳解答:

1. % by mass of hydrogen = 100% - 82.8% = 17.2% ===== 2. Mole ratio C : H = 82.8/12 : 17.2/1 = 6.9 : 17.2 = 2 : 5 Empirical formula = C2H5 ===== 3. Molar mass of the hydrocarbon = 2.42 x 24 = 58.08g/mol ===== 4. Let (C2H5)n be the molecular formula ofthe hydrocarbon. Molar mass of the hydrocarbon : n(12x2 + 1x5) = 58.08 29n = 58.08 n = 2 Molecular formula = C4H10 2013-06-02 19:53:51 補充： Each mole of a gas occupies 24 dm3, i.e. 24 dm3/mol. Molar mass of the hydrocarbon = (2.42 g/dm3) x (24 dm3/mol) = 58.08 g/mol 2013-06-02 19:53:59 補充： Each mole of a gas occupies 24 dm3, i.e. 24 dm3/mol. Molar mass of the hydrocarbon = (2.42 g/dm3) x (24 dm3/mol) = 58.08 g/mol

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