Question

A standard SCUBA diving tank holds 10.9 L of compressed air at 204.1 atm. a. What are the mole fractions of N2 (Tc = 126.20K and Pc = 33.5 atm) and O2 (Tc = 154.4K and Pc = 49.7 atm) in air?

b. Determine how many moles of air are in this tank when filled, assuming the tank is at 25°C.

Answer 1

Since we all know the ideal gas equation PV=nRt ; using that we can calculate no. of moles

firstly we will calculate moles of air ; using above n= PV/RT (R = 0.0821 L-atm/mole-K)

N Of Air(comprises of n of all components present in air)= 204.1atm x 10.9L / 0.0821L-atm/mole-K x (25+273)K

                                                                                        = 90.93moles

as such no.of moles of N2 = 33.5 x 10.9/0.0821 x 126.20 = 35.2426

now no. of moles of O2 = 49.7 x 10.9/0.0821 x 154.4 = 42.735

now as the mole fraction of a gas is equal to the moles of that component divided by the sum of moles ofall component present in air(ie. moles of air) .

so mole fraction of N2 = 35.2426 / 90.93 = 0.3875

and mole fraction of O2 = 42.735 / 90.93 = 0.46997