Question

Oxygen is present in a 1 litre flask at a pressure of $7.6\times {10}^{-10}$ mm Hg. Calculate the number of oxygen molecular in the flask at $0^{\circ }C$.
A. $2.7\times {10}^{10}$
B.$4.7\times {10}^{10}$
C.$2.7\times {10}^{23}$
D. $5\times {10}^{37}$

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

$P=7.6\times {10}^{-10}mm=\frac{7.6\times {10}^{-10}}{760}atm={10}^{-12}atm$
$V=1litre,R=.0821litreatm{K}^{-1}mo{l}^{-1}$ , T = $0^{0}C=273K$
Using ideal gas equation, PV=nRT
$n=\frac{PV}{RT}=\frac{{10}^{12}\times 1}{0.821\times 273}=0.0446\times {10}^{12}$
Number of molecules =n$\times N_A$
= 0.446$\times {10}^{12}\times 6.022\times {10}^{23}=2.68\times {10}^{10}=2.7\times {10}^{10}$