Question

$120 \;g$ of an organic compound that contains only carbon and hydrogen gives $330$ $g$ of $CO_2$ and $270$ $g$ of water on complete combustion. The percentage of carbon and hydrogen, respectively are

• A. 25 and 75
• B. 40 and 60
• C. 60 and 40
• D. 75 and 25

Answer 1

Answer: (D)

75 and 25

Answer 2

Mass of organic compound = $120$ $g$

Mass of $CO_2 = 330$ $g$

Moles of $CO_2 = \frac{330}{44}= 7.5$

Mass of carbon = $7.5 × 12 = 90$ $gm$

Percentage of Carbon = $\frac{90}{120} × 100 = 75\%$

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Mass of $H_2O = 270$ $g$

Moles of $H_2O = \frac{270}{18}= 15$

Mass of hydrogen = $15 × 2 = 30$ $gm$

Percentage of Hydrogen = $\frac{30}{120} × 100 = 25\%$