Question

(a) Define gram molecular mass of a substance. How much is the gram molecular mass of oxygen ?
(b) If sulphur exists as S₈ molecules, calculate the number of moles in 100 g of sulphur. (S = 32 u)

Answer 1

(a) Gram molecular mass refers to the mass of a molecules in one mole of molecules of that substance. It is equal to the gram molecular weight of that element.
Oxygen exists as a diatomic molecule (O₂); therefore, gram molecular mass of oxygen is 32 grams.

(b)
Mass of sulphur = 100g (sulphur exists as S8 molecules)
molecular mass of sulphur = (8 × 32) = 256g
Number of moles in 256g of sulphur = 1 mole
Therefore, number of moles in 100g of sulphur = 100/256 = 0.39 moles
Hence, 100g of sulphur contains 0.39 moles of sulphur.