QJEEM16Cha766: JEE Main 2016 Chemistry - Class 11 JEEM16Cha766 Solution: 5 L of an alkane requires 25 L of oxygen for its complete…

We know, conbustion of Hydrocarbon

C_x H_y + (x + ${y \over 4}$ )O₂   $\to$   x CO₂ + ${y \over 2}$ H₂O

So, to consume 1 mole of C_x H_y we need

(x + ${y \over 4}$ ) mole of O₂ gas.

As both C_x H_y and O₂ are gas,

So avogadro's law is applicable on them.

At constant temperature and pressure according to avogadro's law, volume $\propto$ mole

So, for 5L of C_x H_y the

volume of O₂ = 5(x + ${y \over 4}$ )

According to the question,

5(x + ${y \over 4}$ ) = 25

$\therefore\,\,\,$ (x + ${y \over 4}$ ) = 5 . . . . . (1)

For Ethane (C₂ H₆), x = 2 and y = 6

$\therefore\,\,\,$ x + ${y \over 4}$ = 2 + ${6 \over 4}$ $\ne$ 5

$\therefore\,\,\,$ C₂ H₆ can't be the required alkane.

For Propane (C₃ H₈), x = 3. and y = 8

$\therefore\,\,\,$ x + ${y \over 4}$ = 3 + ${8 \over 4}$ = 5

$\therefore\,\,\,$ Propane (C₃ H₈) is the right alkane.

Similarly for Butane (C₄ H₁₀) and Isobutane (C₄ H₁₀) you can check
x + ${y \over 4}$ $\ne$ 5.