Question

How many molecules of $C{O}_2$ are contained in one litre of air if the volume contained of $C{O}_2$ is $0.03\%$ at $NTP$?

Answer 1

Volume of $C{O}_2$ contained in one litre of air= $\frac{0.03}{100}\times 1000$

=$0.3mL$

At NTP, $T=293k$, $P=1$ atm

and $V=0.3\times {10}^{-3}L$

$\therefore$ $PV=nRT$

$\therefore$ $n=\frac{PV}{RT}=\frac{1\times 0.3\times {10}^{-3}}{0.0821\times 293}=1.25\times {10}^{-5}$ moles

$\therefore$ No. of molecules of $C{O}_2=n\times 6.022\times {10}^{23}$

=$1.25\times {10}^{-5}\times 6.022\times {10}^{23}$

$\therefore$ No. of molecules of $C{O}_2$=$7.51\times {10}^{18}$ molecules