10 mL of gaseous hydrocarbon on combustion gives 40 mL of CO 2 g and 50 mL of water vapour. Total number of carbon and hydrogen atoms in the hydrocarbon is _______.

Question

TestHub · Accepted Answer

The combustion reaction can be represented as

$C_{x} H_{y} + (x + \frac{y}{4}) O_{2} \to {xCO}_{2} + {yH}_{2} O$

At STP, $1$ mole of any gas occupies $22.4 L$

$10 mL$ of hydrocarbon, $50 mL$ of water and $40 mL$ of carbon dioxide corresponds to $0.45, 2.23$ , and $1.79$ moles respectively.

Hence, the combustion of $1$ mole of hydrocarbon will produce $5$ moles of water and $4$ moles of carbon dioxide.

Thus, the molecular formula contains $4$ carbon atoms and $10$ hydrogen atoms.

The hydrocarbon is $C_{4} H_{10}$ and the combustion reaction is

$C_{4} H_{10} + 6.5 O_{2} \to 4 {CO}_{2} + 5 H_{2} O$

$x + y = 4 + 10 = 14$

Hence the Total number of carbon and hydrogen atoms in the hydrocarbon is $14$ .

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