Anonymous

# 化學問題...(英文好的比較適合進來)

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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1.

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%

2.

Mole ratio Fe : Si

= 46.01/55.9 : 53.99/28.1

= 0.8231 : 1.921

= 3 : 7

Empirical formula = Fe3Si7

3.

(a)

Molecular mass of oxygen = 16x2 = 32

Molecular mass of the compound = 32 x 1.94 = 62.1

(b)

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