The molecular formula for elemental sulphur is S₈. In a sample of 5.12 g of sulphur:

(a) How many moles of sulphur are present?

(b) How many molecules and atoms are present?

(a) Mass of 1 mole of S₈ = 8S = 8 x 32 = 256 g

∴ Moles in 5.12 g of sulphur = $\dfrac{5.12}{256}$ = 0.02 moles

(b) 1 mole = 6.022 × 10²³ molecules

∴ 0.02 moles will have = 0.02 × 6.022 × 10²³
= 1.2044 × 10²² ≈ 1.2 × 10²² molecules

No. of atoms in 1 molecule of S₈ = 8

∴ No. of atoms in 1.2044 × 10²² molecules = 1.2044 x 10²² × 8

= 9.635 × 10²² molecules