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Combustion of 0.45 g of an organic compound containing only C, H and O gives 0.66 g of CO2 and 0.27 g of H2O. The vapour density of the compound is…

Numerical answer

Combustion of

0.45\ \mathrm{g}

of an organic compound containing only C, H and O gives

0.66\ \mathrm{g}

\mathrm{CO_2}

and

0.27\ \mathrm{g}

\mathrm{H_2O}

. The vapour density of the compound is

45

. The total number of atoms present in one molecule of the compound is

Show answer and solution

Answer: 12

Carbon

=\dfrac{12}{44}\times0.66=0.18\ \mathrm{g}

(

0.015

mol); hydrogen

=\dfrac{2}{18}\times0.27=0.030\ \mathrm{g}

(

0.030

mol); oxygen by difference

=0.45-0.21=0.24\ \mathrm{g}

(

0.015

mol). Ratio C:H:O

=1:2:1

, empirical formula

\mathrm{CH_2O}

(mass

30

). Molar mass

=2\times\text{VD}=90

, so the factor is

3

: molecular formula

\mathrm{C_3H_6O_3}

with

3+6+3=12

atoms.

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