Question

An open flask sitting in a lab fridge looks empty, but we know that actually it is filled with a mixture of gases called air. If the flask volume is 1.50 L, and the air is at standard temperature and pressure, how many gaseous molecules does the flask contain?

Answer 1

STP conditions,

   P = 1 bar = 0.987 atm

   T = 273.15 k

from ideal gas equation

   PV = nRT

   n = PV/RT

v = 1.5 L

R = 0.0821 l.atm.k-1.mol-1

n = no of mol of air in the flask = ?

n = 0.987*1.5/(0.0821*273.15)

    = 0.066 mol

at STP , 1 mol of any gas contains N0 = 6.023*10^23 molecules

No of air molecules present in flask (N) = n*N0

                                         = 0.066*6.023*10^23

                   = 3.975*10^22 molecules