Question

Find out the molar masses of the following compounds :

a. Copper sulphate crystal (CuSO₄.5H₂O)

b. Sodium carbonate, decahydrate 

(Na₂CO₃.10H₂O)

c. Mohr’s salt [FeSO₄(NH₄)2SO₄.6H₂O]

(At. mass : Cu = 63.5; S = 32; O = 16; H = 1; Na = 23; C = 12; Fe = 56; N = 14)

Answer 1

a. Molar mass of CuSO₄.5H₂O

= (1 × At. mass Cu) + (1 × At. mass S) + (9 × At. mass O) + (10 × At. mass H)

= (1 × 63.5) + (1 × 32) + (9 × 16) + (10 × 1) 

= 63.5 + 32 + 144 + 10

= 249.5 g mol^-1

Molar mass of CuSO₄.5H₂O = 249.5 g mol^-1

b. Molar mass of Na₂CO₃.10H₂O

= (2 × At. mass Na) + (1 × At. mass C) + (13 × At. mass O) + (20 × At. mass H)

= (2 × 23) + (1 × 12) + (13 × 16) + (20 × 1) 

= 46 + 12 + 208 + 20

= 286 g mol^-1

Molar mass of Na₂CO₃.10H₂O = 286 g mol^-1

c. Molar mass of [FeSO₄(NH₄)₂SO₄.6H₂O]

= (1 × At. mass Fe) + (2 × At. mass S) + (2 × At. mass N) + (14 × At. mass O) + (20 × At. mass H)

= (1 × 56) + (2 × 32) + (2 × 14) + (14 × 16) + (20 × 1) 

= 56 + 64 + 28 + 224 + 20

= 392 g mol^-1

∴ Molar mass of [FeSO₄(NH₄)2SO₄.6H₂O] = 392 g mol^-1