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JAMB Chemistry 1986 Question 2

Question 2

Mole Concept and Stoichiometry

What mass of a divalent metal M (atomic mass = 40) would react with excess hydrochloric acid to liberate 224 cm3 of dry hydrogen gas measured at S.T.P? [G.M.V = 22.4 dm3]

  1. A.8.0 g
  2. B.4.0 g
  3. C.0.8 g
  4. D.0.4 g
Show the answer and explanation

Answer: D (0.4 g)

Explanation

M + 2HCl → MCl2 + H2, so 1 mol of M gives 1 mol of H2. 224 cm3 is 0.01 mol of H2, so 0.01 × 40 = 0.4 g of M is needed.