Samples of O2, N2, CO and CO2 under the same conditions of temperature and pressure contain the same number of molecules represented by X. The molecules of oxygen occupy V litres and have a mass of 8 g. Under the same conditions of temperature and pressure, what is the volume occupied by :
(i) X molecules of N2.
(ii) 3X molecules of CO.
(iii) What is the mass of CO2 in grams.
(iv) In answering the above questions, whose law has been used.
[C = 12, N = 14, O = 16]

By Avogadro’s law: Under the same conditions of temperature and pressure equal volumes of all gases contain the same number of molecules.

∴ If gases under the same conditions have same number of molecules then they must have the same volume.

(i) So, X molecules of N₂ occupy V litres.

(ii) 3X molecules of CO will occupies 3V litres.

(iii) Molar mass of CO₂ = C + 2(O) = 12 + 2(16) = 44 g

1 mole of O₂ weighs 32 g and occupy 22.4 lit. volume

∴ 8 g of O₂ will occupy = 22.4\over32 × 8

= 5.6 lit. vol.

= Molar volume

If 8 g of O₂ occupies 5.6 lit. vol.

And 1 mole of CO₂ occupies 22.4 lit and weighs = 44 g at s.t.p.

∴ 5.6 lit. vol. of CO₂ will weigh = 44\over22.4 × 5.6

= 11 g

Hence, mass of CO₂ = 11 g

(iv) Avogadro’s Law is used above.