Oxygen is present in a 1-litre flask at a pressure of 7.6 xx 10^(-10) mmHg at 0°C. Calculate the number of oxygen molecules in the flask.

Oxygen is present in a 1-litre flask at a pressure of 7.6 xx 10^(-10)

1.	Oxygen is present in a 1-litre flask at a pressure of 7.6 xx 10^(-10) mmHg at 0°C. Calculate the number of oxygen molecules in the flask.
Answer» Solution :PRESSURE `=7.6 xx 10^(-10)` mm `=0.76 xx 10^(-10) cm` `=(0.76 xx 10^(-10))/76` ATM (1 atm = 76 cm) `=10^(-12)` atm Volume = 1 litre, R = 0.0821 lit. Atm/K/mole. Temperature = 273 K We know that pV = nRT or `n=(pV)/(RT)` `n=(10^(-12) xx 1)/(0.0821 xx 273) = 0.44 xx 10^(-13)` No. of molecules = no. of MOLES `xx` AV. const. `=0.44 xx 10^(-13) xx 6.022 xx 10^(23) = 2.65 xx 10^(10)`