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)

Given mass of organic compound $=120$
mass of $CO _{2}( g )=330\, g$
mass of $H _{2} O (\ell)=270\, g$
mass of carbon $= n _{ CO _{2}} \times 12$
$=\frac{330}{44} \times 12=90\, g$
$\%$ of carbon $=\frac{90}{120} \times 100=75 \%$
mass of hydrogen $= n _{ H _{2} O } \times 2$
$=\frac{270}{18} \times 2=30\, g$
$\%$ of hydrogen $=\frac{30}{120} \times 100=25 \%$