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Unilorin Post-UTME Chemistry 2023 (Model questions) Question 4

Question 4

Chemical Formulae and Equations

What is the molecular formula of a compound that contains 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass? Take the relative molecular mass of the compound as 180 (C = 12, H = 1, O = 16)

  1. A.CH2O
  2. B.C4H8O4
  3. C.C6H12O6
  4. D.C5H8O7
Show the answer and explanation

Answer: C (C6H12O6)

Explanation

Mole ratio C : H : O = 40/12 : 6.7/1 : 53.3/16 = 3.33 : 6.7 : 3.33 = 1 : 2 : 1, so the empirical formula is CH2O (mass 30). 180 ÷ 30 = 6, giving C6H12O6.