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JAMB Chemistry 2011 Paper

Question : 38

Total: 47

[C = 12, H = 1, O = 16]

Solution:

Concept:

Molecular formula is a whole-number multiple of the empirical formula, found using molar mass.

Explanation:

Vapour density is half the molar mass of the gas.

So, molar mass

= 2 \times 45 = 90

Empirical formula is

\mathrm{CH_2O}

Empirical formula mass

= 12 + 2(1) + 16 = 30

Let the molecular formula be

(\mathrm{CH_2O})_n

n = \frac{90}{30} = 3

Therefore, molecular formula is

(\mathrm{CH_2O})_3 = \mathrm{C_3H_6O_3}

Answer:

\mathrm{C_3H_6O_3}

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