Question

Calculate the mass and volume of oxygen at S.T.P., which will be evolved on electrolysis of 1 mole (18 g) of water.

Answer 1

\[\ce{2H2O ->[Electrolysis] 2H2 + O2}\]

2 moles of H₂O gives = 1 mole of O₂

So, 1 mole of H₂O will give = 0.5 moles of O₂

so, mass of O₂ = no. of moles x molecular mass

= 0.5 × 32 = 16 g of O₂

and 1 mole of O₂ occupies volume = 22.4 litre

so, 0.5 moles will occupy = 22.4 × 0.5 = 11.2 litres at S.T.P.