WAEC Chemistry 2010 Theory — Question 27
Question 27 of 46 from the West African Examinations Council (WAEC) Chemistry 2010 Theory paper, with the correct answer and a full explanation.
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4a(iii) A hydrocarbon with a vapour density of 29 contains 82.76% carbon and 17.24% hydrogen. Determine: I. empirical formula; II. molecular formula of the hydrocarbon. [H=1.00, C=12.00]
Model answer
C: 82.76/12 = 6.9967. H: 17.24/1 = 17.24. Dividing by the smaller (6.9967): C=1, H=2.4643≈2.5. Multiplying through by 2: C2H5. Empirical formula = C2H5. RMM = 2x29 = 58. Molecular formula (C2H5)n = 58, giving (2x25+5)n = 58, 29n=58, n=2. Molecular formula = C4H10.
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