Answer to Question #152377 in General Chemistry for O.Weerasinghe

Question

The water vapor formed after the complete combustion of 18cm3 of gaseous compound containing only C, H with O2, 162cm3 was counted. The volume of the remaining gas is 126cm3. If so, find the molecular formula of the compound. Explain with steps.

Answer 1

C_xH_y + O₂ → CO₂ + H₂O

C_xH_y + (x+y/4)O₂ → xCO₂ + (y/2)H₂O

V(C_xH_y) = 18 cm³

V(H₂O) = 162 cm³

V(CO₂) = 126 cm³

$\frac{n(CO_2)}{n(C_xH_y )} = \frac{x}{1} = \frac{126}{18} \\ x = 7 \\ \frac{n(CO_2)}{n(H_2O)} = \frac{x}{\frac{y}{2}} \\ \frac{2x}{y} = \frac{126}{162} \\ \frac{14}{y} = \frac{126}{162} \\ y = 18$

Answer: C₇H₁₈