Question

Oxygen is present in a 1-liter flask at a pressure of $7.6\times {10}^{-10}$ mm of Hg at $0^{o}C$. Calculate the number of oxygen molecules in the flask.

• A. $3.65\times {10}^9$
• B. $2.65\times {10}^{10}$
• C. $5\times {10}^{10}$
• D. $2.65\times {10}^{-10}$

Answer 1

The correct option is B $2.65\times {10}^{10}$

Pressure = $7.6\times {10}^{-10}$ mm Hg

= $\frac{7.6\times {10}^{-10}}{760}$ [1 atm = 760 mm Hg]

= ${10}^{-12}$ atm

Volume = 1 liter

Temperature = $0^{o}C$ = 273 K

We know $pV=nRT\to n=\frac{pV}{RT}$

n = $\frac{{10}^{-12}\times 1}{0.0821\times 273}=0.44\times {10}^{-13}$

No. of molecules = $no.ofmoles\times Avogadroconstant$

= $0.44\times 10{}^{-}13\times 6.022\times {10}^{23}$

= $2.65\times {10}^{10}$.

answer is B