Single Choice

Twenty millilitres of a gaseous hydrocarbo required $$400 ml$$ of air for complete combustion. The air contains $$20\%$$ by volume of oxygen. The volume of gaseous mixture after explosion and cooling was found to be $$380 ml$$. Formula of hydrocarbon is:

A$$C_{3}H_{8}$$
B$$C_{3}H_{6}$$
C$$C_{3}H_{4}$$
Correct Answer
D$$C_{2}H_{6}$$

Solution

$$C_{x}H_{y} + (x+\dfrac{y}{4})O_{2} \rightarrow xCO_{2}+\dfrac{y}{2}H_{2}O$$

$$1 ml\ \ \ \ \ (x+\dfrac{y}{4})ml\ \ \ \ \ \ \ x\ ml$$

$$20 ml\ \ \ \ 20(x+\dfrac{y}{4})ml\ \ \ \ \ \ 20x\ ml$$

$$\therefore 20x = 60,\ x=3$$

$$20(x+\dfrac{y}{4})=80$$

$$\therefore y=4$$

Formula of hydrocarbon = $$C_{3}H_{4}$$ {Option (C)}

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