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WAEC Chemistry 2018 Theory — Question 15

Question 15 of 24 from the West African Examinations Council (WAEC) Chemistry 2018 Theory paper, with the correct answer and a full explanation.

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3.(a)(i) Draw the structure of the sixth member of the alkene series. (ii) Calculate the relative molecular mass of the sixth member of the alkene series. [H=1, C=12] (iii) State one difference between cracking and reforming in the petroleum industry.

Model answer

(i) The sixth member of the alkene series is heptene, C₇H₁₄ (structure: a 7-carbon chain with one C=C double bond). (ii) Molecular mass = (12×7)+(1×14) = 98. (iii) Cracking involves breaking large hydrocarbon molecules into smaller ones, while reforming involves the re-arrangement of atoms within molecules without necessarily changing their size.

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