Question

What volume of air containing 21% oxygen by volume is required to completely burn 1 kg of carbon containing 100% combustible substances ?

Answer 1

Combustion of carbon may be given as,
$C\left(s\right)+O_2\left(g\right)\to C{O}_2\left(g\right)$
$\therefore$ 12 g carbon requires 1 mole $O_2$ for complete combustion
$\therefore$ 1000 g carbon will require $\frac{1}{12}\times 1000$ mole $O_2$ for combustion, i.e., 83.33 mole $O_2$
Volume of $O_2$ at $NTP=83.33\times 22.4litre=1866.592litre$
$\because$ 21 litre $O_2$ is present in 100 litre air .
$\therefore$ 1866.592 litre $O_2$ will be present $\frac{100}{21}\times 1866.592litre{O}_2$
$=8888.5litre=8.8885\times {10}^{3}litre$