Question

20ml of a hydrocarbon requires 100ml of oxygen under the same conditions for complete combustion. 60ml of carbon dioxide is formed. The formula of hydrocarbon is?​

Answer 1

The hydrocarbon is   $C_3H_8$   and the combustion reaction is $C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O$

Step-by-step explanation:

We know that, AT STP, $1 \ mole$ of any gas occupies $22.4 \ Litre$.

$20 ml$ of hydrocarbon $= 0.89 \ moles$

$100 ml$ of oxygen $= 4.46 \ moles$

$60 ml$ of carbon dioxide $= 2.67 \ moles$

Hence, the combustion of 1 mole of hydrocarbon will require 5 moles of oxygen and will produce 3 moles of carbon dioxide.

Thus, the molecular formula contains 3 carbon atoms.

Out of 5 moles of oxygen, 3 moles will combine with carbon to form 3 moles of carbon dioxide.

The remaining two moles of oxygen will combine with 8 moles of hydrogen atoms (from the hydrocarbon) to form 4 moles of water.

Thus, the molecular formula contains 8 hydrogen atoms.

The hydrocarbon is $C_3H_8$ and the combustion reaction is $C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O$