Combustion of 10ml of a gaseous hydrocarbon gives 40ml of CO2 and 50ml of water vapour under the same conditions. The molecular formula of the hydrocarbon is
Let CαHh be the 10‌mL of gaseous hydrocarbon that produces 40‌mL of CO2 and 50‌mL of water So, CaHb+(a+‌
b
4
)O2→aCO2+‌
b
2
H2O ‌10‌mL+‌ excess→‌‌‌0‌‌‌‌0 ‌‌‌‌‌0‌‌‌+‌ excess →‌‌10a‌‌5b Ratio of volume is =10:40:50=1:4:5 All carbon from hydrocarbon is in the CO2. 10‌mL of hydrocarbon produces 40‌mL of CO2. ∴1:4 ratio. So, 1 mole of hydrocarbon has four moles of carbon. 10‌mL of hydrocarbon produces 50‌mL water. i.e. 1 : 5 ratio. Each water molecule has 2 moles of H-atom. So, 1 mole hydrogen carbon compound has 10 moles of hydrogen. ∴ The molecular formula of the hydrocarbon is C4H10.