Question

Oxygen is present in a one litre flask at a pressure $7.6\times {10}^{-10}mm$ of $Hg$. Calculate the number of oxygen molecules in the flask at $0^{\circ }C$.

Answer 1

Using ideal gas equation,

$n=\frac{PV}{RT}....\left(i\right)$
$P=\frac{7.6\times {10}^{-10}}{760}={10}^{-12}atm$
$V=1L,T=273K,R=0.0821Latm{K}^{-1}mo{l}^{-1}$
From eq. (i) $n=\frac{{10}^{-12}\times 1}{0.0821\times 273}$
Number of molecules $=n\times 6.023\times {10}^{23}$
$=\frac{{10}^{-12}}{0.0821\times 273}\times 6.023\times {10}^{23}$
$=2.68\times {10}^{10}$