Question

An alkane on complete combustion required 8 moles of O₂. Find out the number of carbon and hydrogen in the alkane.

Hint:

In combustion reactions, the stoichiometry helps us determine the composition of the molecule by relating oxygen required to the number of carbon and hydrogen atoms.

Answer 1

Correct Answer: 10

The general combustion reaction for an alkane is:

\[C_nH_{2n+2} + O_2 \rightarrow CO_2 + H_2O\]

 

For complete combustion, the number of moles of oxygen required is given by:

\[\text{Oxygen required} = \left( n + \frac{2n+2}{2} \right) = \frac{3n+2}{2}\]

 

Given that 8 moles of oxygen are required for complete combustion, we set up the equation:

\[\frac{3n+2}{2} = 8\]

 

Multiplying both sides by 2:

\[3n + 2 = 16\]

Solving for \(n\):

\[3n = 14\]

\[n = \frac{14}{3} \approx 4.67\]

 

Since the number of carbon atoms must be an integer, the alkane is approximately C₄H₁₀. Thus, the alkane has 4 carbon atoms and 10 hydrogen atoms.

\[\boxed{C_4H_{10}}\]

Hence, the correct number of carbon and hydrogen atoms is C₄H₁₀.