1. "Q-gas" is a mixture of 98.70% He and 1.30% C4H10 (butane) by mass. Compute the mass percentage of Hydrogen in Q-gas.
2. Sand frlgurites contain some grains of the definite chemical composition Fe 46.01%, Si 53.99%. Determine the empirical formula of these grains.
3. A gaseous binary compound has a vapor density that is 1.94 times that of oxygen at same T and P. When 1.39g of the gas is burned in an excess of oxygen, 1.21g of water is formed, removing all hydrogen originally present.
(a) Estimate the molecular mass of the gaseous compound.
(b) How many H atoms are there in a molecule of the compund?
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- 老爺子Lv 71 decade agoFavorite Answer
Let m g be the mass of Q-gas.
Molar mass of H = 1 g/mol
Molar mass of C4H10 = 12x4 + 1x10 = 58 g/mol
Mass of H in C4H10 = m x 1.30% x (1x10/58) = 0.00224m g
Mass % of H in Q-gas = (0.00224m/m) x 100% = 0.224%
Mole ratio Fe : Si
= 46.01/55.9 : 53.99/28.1
= 0.8231 : 1.921
= 3 : 7
Empirical formula = Fe3Si7
Molecular mass of oxygen = 16x2 = 32
Molecular mass of the compound = 32 x 1.94 = 62.1
Molecular mass of H2O = 1x2 + 16 = 18
No. of moles of the compound used = 1.39/62.1 = 0.0224 mol
No. of moles of H2O formed = 1.21/18 = 0.0672 mol
No. of moles of H atoms in the compound = 0.0672 x 2 = 0.134 mol
No. of H atoms in a molecule of the compound = 0.134/0.0224 = 6