Question

A vessel of volume 20l contains a mixture of hydrogen and helium at temperature of 27c and pressure 2.0 atm. The mass of the mixture is 5g. Assuming the gases to be ideal, the ratio of mass of hydrogen to that of helium in the given mixture will be

Answer 1

Let there are n1 moles of hydrogen and n2 moles of helium in the given mixture. As Pv = nRT Then the pressure of the mixture

p=n1RTV+n2RTV=(n1+n2)RTV

⇒2×101.3×103 = (n1+n2)×(8.3×300)20×10−3

or(n1+n2)=2×101.3×10320×10−3(8.3)(300)

or,n1+n2=1.62.....(1)

The mass of the mixture is (in grams)

n1×2+n2×4=5

⇒(n1+2n2)=2.5....(2)

Solving the eqns.(1) and (2), we get

n1=0.74 and n2=0.88

Hence, H/He==0.74×20/88×4=1.48/3.52=2/5