f5 chem (20points)

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

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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
=