Question

The complete combustion of 15.0 cm3 of a gaseous hydrocarbon x produces 60.0 cm3 of carbon dioxide gas and 75.0 cm3 of water vapour. What is the molecular formula of x? (all volumes are measured at the same temperature and pressure.)

Answer 1

Answer:

Let CₙHₘ be the molecular formula of Z.

Balanced equation for the reaction:

4 CₙHₘ + (4n + m) O₂ → 4n CO₂ + 2m H₂O

At r.t.p., volume ratio CₙHₘ : O₂ : CO₂ = 4 : (4n + m) : 4n

In the experiment, volume ratio CₙHₘ : O₂ : CO₂ = 1 : 4 : 3

Volume ratio CₙHₘ : CO₂ = 4 : 4n = 1 : 3

4n = 12

n = 3

volume ratio CₙHₘ : O₂ = 4 : (4×3 + m) = 1 : 4

12 + m = 16

m = 4