Question

At STP conditions the number of moles of
oxygen in a litre of air which has 21% oxygen
by volume is -
[AIPMT-95]
(1) 2.10 mole (2) 0.0093
(3) 0.186 mole (4) 0.21 mole​

Answer 1

Explanation:

Volume percentage is defined as

Volume per cent = (volume of solute/ volume of solution) X 100

Given the volume % is 21.

Let VO be the volume of O2 present in 1 litre of air.

Therefore we have,

21 = (VO/1) X 100

VO = 21/100 = 0.21 litres of Oxygen gas.

Now 22.4 litres of O2 gas = 1 mole of O2 gas.

Therefore 1 litre of O2 gas = 1/22.4 moles of O2 gas.

So 0.21 Litres of O2 gas = (1/22.4) X 0.21 = 0.0094 moles.

Answer 2

At STP conditions the number of moles of

oxygen in a litre of air which has 21% oxygen

by volume is - 0.0093 moles