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JAMB Chemistry 1984 Question 28

Question 28

Chemical Formulae and Equations

An organic compound with a vapour density 56.5 has the following percentage composition: C = 53.1%, N = 12.4%, O = 28.3%, H = 6.2%. The molecular formula of the compound is (Relative atomic masses: N = 14, O = 16, C = 12, H = 1)

  1. A.C3H6O2N
  2. B.C5H6O2N
  3. C.(C5H7O2N)½
  4. D.C5H7O2N
  5. E.(C5H7O2N)2
Show the answer and explanation

Answer: D (C5H7O2N)

Explanation

Moles: C 53.1/12 = 4.43, N 12.4/14 = 0.886, O 28.3/16 = 1.77, H 6.2/1 = 6.2; dividing by 0.886 gives C5H7O2N (mass 113). Relative molecular mass = 2 × 56.5 = 113, so the molecular formula is C5H7O2N.