Question

A flask contains 3.2 g of sulphur dioxide. Calculate the following:

1. The moles of sulphur dioxide present in the flask.
2. The number of molecules of sulphur dioxide present in the flask.
3. The volume occupied by 3.2 g of sulphur dioxide at STP

(S = 32, O = 16)

Answer 1

Molecular mass of SO₂ = [32 + 2(16)] = 64 g

64 g of SO₂ is equal to 1 mole.

(i) 3.2 of SO₂ = `1/64 xx 3.2`

= 0.05 mole

(ii) 1 mole of SO₂ = 6.02 × 10²³ molecules

∴ 0.05 mole of SO₂ = 0.05 × 6.02 × 10²³

= 3.01 × 10²² molecules

(iii) 1 mole of SO₂ has volume at STP = 22.4 lit.

∴ 0.05 mole of SO₂ has volume at STP = 0.05 × 22.4

= 1.12 litres