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標題:
f5 chem (20points)
發問:
1) 2.90g of a metal oxide(M2O) deccompose completely into its elements on heating to give 150cm^3 of oxyben measured at room conditions. Calculate (a) formula mass of M2O (b) atomic mass of M.2) 1.2g of a gaseous hydrocarbon Z are burnt completely in excess of dry oxygen in a suitable apparatus, and the resulting... 顯示更多 1) 2.90g of a metal oxide(M2O) deccompose completely into its elements on heating to give 150cm^3 of oxyben measured at room conditions. Calculate (a) formula mass of M2O (b) atomic mass of M. 2) 1.2g of a gaseous hydrocarbon Z are burnt completely in excess of dry oxygen in a suitable apparatus, and the resulting gas is led through concentrated sulphuric acid. The acid increases in mass by 1.86g. Calculate the empirical formula of Z. 2.0 dm^3 of Z, when measured at s.t.p., weigh 5.178g. Deduce the molecular formula of Z
最佳解答:
1)a) Molar volume of a gas at room conditions = 24000 cm3 2M2O → 4M + O2 Mole ratio M2O : O2 = 2 : 1 No. of moles of O2 formed = 150/24000 = 0.00625 mol No. of moles of M2O reacted = 0.00625 x 2 = 0.0125 mol Molar mass of M2O = mass/mol = 2.9/0.0125 = 232 g mol-1 Formula mass of M2O = 232 1)b) Relative atomic mass of O = 16 Let y be the atomic mass of M. 2y + 16 = 232 2y = 216 y = 108 The relative atomic mass of M = 108 ===== 2) Molar mass of C = 12 g mol-1 Molar mass of H = 1 g mol-1 Molar mass of H2O = 18 g mol-1 Mass fraction of H in H2O = (1x2)/18 = 1/9 The conc. H2SO4 absorbed all H2O formed in combustion of Z. Mass of H2O formed = 1.86 g Mass of H in H2O formed = 1.86 x (1/9) = 0.206 g In 1.2 g of the hydrocarbon Z: Mass of O = 0.206 g Mass of C = 1.2 - 0.206 = 0.994 In Z, mole ratio C : H = (0.994/12) : (0.206/1) = 0.0828 : 0.206 = 2 : 5 The empirical formula of Z = C2H5 The molar volume of a gas at s.t.p. = 22.4 dm3 For 2.0 dm3 of Z: No. of moles of Z = vol/(molar vol) = 2/22.4 = 0.0893 mol Molar mass of Z = mass/mol = 5.178/0.0893 = 58 g mol-1 Let (C2H5)n be the molecular formula of Z. n(12x2 + 1x5) = 58 29n = 58 n = 2 The molecular formula of Z = C4H10 =
其他解答:C8D74AB62542840B
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