Question

What percentage of water is present in

1. Hydrated copper sulphate …………

2. Washing soda crystals …….

Answer 1

Answer (1)

• We know that,
• The molecular formula for Hydrated copper sulphate is CuSO₄.5H₂O.
• Molecular weight of Cu = 63.5, S = 32, O = 16, H = 1.
• Total molecular weight of CuSO₄.5h₂O is 63.5 + 32 + 4(16) + 5[2 (1)+16] = 249.5 g.
• The total weight of water is 5[2(1) + 16]=90
• Then the percentage weight of water in Hydrated copper sulphate is [ (Total weight of water ÷ total weight of CuSO₄.5H₂O) x 100].
• Percentage of water is present in Hydrated copper sulphate = (90 ÷ 249.5) x 100 = 36.07%.

Answer (2)

• The molecular formula for Washing soda crystals is Na₂CO₃.10H₂O.
• The molecular weight of Na = 23, C = 12, O = 16, h=1.
• The total molecular weight of Na₂CO₃.10H₂O = (23×2) + 12 + (16×3) + 10(2+16) = 106 + 180 = 286.
• The total weight of water is 10(2+16) = 180.
• Then Percentage of water is present in Washing soda crystals is [ (Total weight of water ÷ total weight of Na₂CO₃.10H₂O0 x 100].
• The percentage of water is present in Hydrated copper sulphate (180 ÷ 286) x 100 = 62.9 g.