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JAMB Chemistry 2019 Paper

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Question : 53

Total: 80

Which of the following could not be alkane?

C $_4$ H $_{10}$
C $_5$ H $_{12}$
C $_7$ H $_{14}$
C $_8$ H $_{18}$

Solution:

Concept:

Alkanes have the general formula

\mathrm{C}_n\mathrm{H}_{2n+2}

.

Explanation:

For

\mathrm{C}_4\mathrm{H}_{10}

,

n=4

, so

2n+2=10

. It fits.

For

\mathrm{C}_5\mathrm{H}_{12}

,

n=5

, so

2n+2=12

. It fits.

For

\mathrm{C}_7\mathrm{H}_{14}

,

n=7

, so

2n+2=16

, not 14. It does not fit.

For

\mathrm{C}_8\mathrm{H}_{18}

,

n=8

, so

2n+2=18

. It fits.

Answer:

\mathrm{C}_7\mathrm{H}_{14}

could not be an alkane.

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