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JAMB Chemistry 2012 Paper

Question : 41

Total: 45

Solution:

Concept:

Find the empirical formula from percentage composition, then multiply it by a whole number using the molecular mass.

Explanation:

In 100 g of the compound:

Moles of C

= \frac{40.0}{12} = 3.33

Moles of H

= \frac{6.7}{1} = 6.7

Moles of O

= \frac{53.3}{16} = 3.33

Divide by the smallest value,

3.33

:

:

= 1 : 2 : 1

Empirical formula

= \mathrm{CH_2O}

Empirical formula mass

= 12 + 2(1) + 16 = 30

n = \frac{\text{Molecular mass}}{\text{Empirical formula mass}} = \frac{180}{30} = 6

Molecular formula

= (\mathrm{CH_2O})_6 = \mathrm{C_6H_{12}O_6}

Answer:

\mathrm{C_6H_{12}O_6}

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