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JAMB Chemistry 1985 Question 4

Question 4

Mole Concept and Stoichiometry

0.499 g of CuSO4.xH2O when heated to constant weight gave a residue of 0.346 g. The value of x is (Cu = 63.5, S = 32.0, O = 16, H = 1).

  1. A.0.5
  2. B.2.0
  3. C.3.0
  4. D.4.0
  5. E.5.0
Show the answer and explanation

Answer: D (4.0)

Explanation

Water lost = 0.499 − 0.346 = 0.153 g = 0.0085 mol. CuSO4 left = 0.346/159.5 = 0.00217 mol. Ratio 0.0085 : 0.00217 ≈ 4, so x = 4.