Question

Which contains more molecules, 10 g of sulphur dioxide (SO2) or 10 g of oxygen (O2) ?

(Atomic masses : S = 32 u ; O = 16 u)

Answer 1

Given:

Mass of sulphur dioxide = 10g

Molar mass of sulphur dioxide = (1 × 32) + (2 × 16) = 64g

We know that 64g of sulphur dioxide contain 6.022 × 10²³ molecules.

Number of molecules in 64g  sulphur dioxide = 6.022 × 10²³

Number of molecules in 10g  sulphur dioxide  = 10 × 6.022 × 10²³/ 64

Hence, the number of molecules in 10g sulphur dioxide is 9.4× 10²².

Given:

Mass of oxygen = 10g

Molar mass of oxygen molecule = (2 × 16) = 32g

Number of molecules in 32g oxygen = 6.022 × 10²³

Number of molecules in 10g oxygen = 10 × 6.022 × 10²³/ 32

Hence, the number of molecules in 10g  oxygen is 18.8 × 10²²

It is clear that the number of atoms in 10g  oxygen is greater than that in 10g  sulphur dioxide.