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# A gas mixture of $3l$ of propane $(C_3H_8)$ and butane $C_4H_{10}$ on complete combustion at $25C^{\large\circ}$ produced $10l$ $CO_2$.Find out the composition of gas mixture.

$(a)\;2l,1l\qquad(b)\;3l,2l\qquad(c)\;4l,3l\qquad(d)\;2l,3l$

$C_3H_8+5O_2\rightarrow 3CO_2+4H_2O(l)$
$C_4H_{10}+\large\frac{13}{2}$$O_2\rightarrow 4CO_2+5H_2O(l)$
Let $a$ litre of $C_3H_8$ and $b$ litre of $C_4H_{10}$ be present in mixture.
$a+b=3$-------(1)
Volume of $CO_2$ formed =10=$CO_2$ formed by $C_4H_{10}$
$10=3a+4b$------(2)
Solving equation (1) and (2)
$b=1l$
$a=2l$
Hence (a) is the correct answer.
selected Nov 6, 2013