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JAMB Chemistry 2003 Question 3

Question 3

Mole Concept and Stoichiometry

What is the percentage by mass of oxygen in Al2(SO4)3.2H2O? [Al = 27, S = 32, H = 1, O = 16]

  1. A.14.29%
  2. B.25.39%
  3. C.50.79%
  4. D.59.25%
Show the answer and explanation

Answer: D (59.25%)

Explanation

Molar mass = 54 + 96 + (14 × 16) + 4 = 378. Oxygen = 224, so % O = 224/378 × 100 ≈ 59.3%.