Question

Ave MW from mas

A gas has a mass compostion of 48.1% nitrogen, 15.4% oxygen, 21.8% carbon dioxide and 14.7 % hydrogen. Determine its average molecular weight.

Answer 1

average moleuclar mass of gas = sum of moles of mole fraction of each gas X molar mass of each gas

So let us calcualt the moles and mole fractions of each gas

Let we have 100grams of gas mixture

1) mass of Nitrogen = 48.1 grams

Moles = mass / molecular weight = 48.1 / 28 = 1.717

2) mass of oxygen = 15.4grams

Moles =15.4 / 32 = 0.481

3) mass fo CO2 = 21.8

Moles = 21.8 / 44 = 0.495

4) mass of hydrogen = 14.7 grams

Moles = 14.7 / 2 = 7.35

So total moles = 7.35 + 0.495 + 0.481 + 1.717 = 10.043

The mole fractions will be

N2 = 1.717 / 10.043 =0.17

O2 = 0.481 / 10.043 = 0.048

CO2 = 0.495 / 10.043 = 0.049

H2 = 7.35 / 10.043 = 0.73

so average molecular weight = 0.17 X 28 + 0.048 X 32 +0.049 X 44+ 0.73 X 2

average molecular weight = 4.76 + 1.536 + 2.156 + 1.46 = 9.912 grams / mole