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The volume of unreacted Oxygen = 1.25 L = 1.25 dm³ = 1250 cm³

Given

Combustion of propane

3.6 L CO2

7.25 L O2

Required

The volume of unreacted oxygen

Solution

Reaction

C₃H₈ + 5O₂ ⇒ 3CO₂ + 4H₂O

Avogadro's :  

In the same T,P and V, the gas contains the same number of molecules  

So the ratio of gas volume will be equal to the ratio of gas moles  

Vol O₂ = 5/3 x vol CO2 = 5/3 x 3.6 = 6 L

The unreacted : 7.25 - 6 = 1.25 L

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