A gas cylinder contains 12 x 10^24 molecules of oxygen gas.
Calculate : (i) the mass of O2 present in the cylinder.
(ii) the volume of O2 at S.T.P. present in the cylinder.
[O = 16] Avog. no. is 6 × 10^23

Gram molecular mass of oxygen = 32 g = 1 mole and contains 6 x 10²³ molecules i.e., 6 x 10²³ molecules weigh 32 g

∴ 12 × 10²⁴ molecules will weigh = 32\over6 × 10^{23} × 12 × 10²⁴

= 640 g

(ii) 6 × 10²³ molecules occupy 22.4 lit. of vol.

∴ 12 × 10²⁴ molecules will occupy = 22.4\over6 × 10^{23} × 12 × 10²⁴

= 448 lit.

Hence, mass of O₂ present in the cylinder = 640 g and volume of O₂ at S.T.P. present in the cylinder = 448 lit.