Question

Calculate the mass per cent of different elements present in sodium sulphate \((\text{Na}_2\text{SO}_4)\).

Answer 1

Step 1: Molar mass of Na₂SO₄

Using approximate atomic masses: Na = 23, S = 32, O = 16.

Molar mass of Na₂SO₄:

• Na: 2 × 23 = 46 g
• S: 1 × 32 = 32 g
• O: 4 × 16 = 64 g

Total molar mass = 46 + 32 + 64 = 142 g·mol⁻¹.

Step 2: Mass percent of each element

Formula: mass percent of element = (mass of that element in 1 mol / molar mass of compound) × 100.

Element	Mass in 1 mol (g)	Mass Percent (%)
Sodium (Na)	46	(46 / 142) × 100 ≈ 32.4%
Sulphur (S)	32	(32 / 142) × 100 ≈ 22.5%
Oxygen (O)	64	(64 / 142) × 100 ≈ 45.1%

Result

Mass percent in Na₂SO₄ (approximate):

• Na ≈ 32.4%
• S ≈ 22.5%
• O ≈ 45.1%