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JAMB Chemistry 1979 Question 42

Question 42

Mole Concept and Stoichiometry

Phosphorus burns in oxygen according to the equation P4 + 5O2 → P4O10. How many litres of oxygen will be required at S.T.P for complete oxidation of 12.4g of phosphorus? (P = 31, O = 16 and molar volume of a gas at S.T.P. = 22.4 litres).

  1. A.5.20
  2. B.11.20
  3. C.2.24
  4. D.20.20
  5. E.6.20
Show the answer and explanation

Answer: B (11.20)

Explanation

P4 = 124 g/mol, so 12.4 g = 0.1 mol. It needs 5 × 0.1 = 0.5 mol O2 = 0.5 × 22.4 = 11.2 litres.