## Mass Transfer Questions and Answers Part-1

1. A binary mixture of oxygen and nitrogen with partial pressures in the ratio 0.21 and 0.79 is contained in a vessel at 300 K. If the total pressure of the mixture is 1 * 10 5 N/m2, find molar fraction of nitrogen
a) 0.21
b) 0.79
c) 0.23
d) 0.13

Explanation: Molar fraction is equal to the partial pressure.

2. For a binary mixture of species A and B, the molar average velocity is defined as
a) n a V a + n b V b
b) n a V a + n b V b/n
c) n a V a + n b V b/2 n
d) n a V a + 2 n b V b/n

Explanation: n A V A + n B V B/n A + n B = n A V A + n B V B/n

3. A binary mixture of oxygen and nitrogen with partial pressures in the ratio 0.21 and 0.79 is contained in a vessel at 300 K. If the total pressure of the mixture is 1 * 10 5 N/m2, find mass fraction of oxygen
a) 0.333
b) 0.433
c) 0.233
d) 0.133

Explanation: 0.269/1.156 = 0.233

4. The ratio of a mass concentration of species A to the total mass density of the mixture is known as
a) Mass density
b) Concentration
c) Mole fraction
d) Mass fraction

Explanation: It is defined as pa/p

5. The ratio of number of moles of species A to the total number of moles of the mixture is known as
a) Mole fraction
b) Partial pressure
c) Mass fraction
d) Mass density

Explanation: It is defined as na/n

6. A binary mixture of oxygen and nitrogen with partial pressures in the ratio 0.21 and 0.79 is contained in a vessel at 300 K. If the total pressure of the mixture is 1 * 10 5 N/m2, find the average molecular weight of the mixture
a) 28.84
b) 29.84
c) 31.84
d) 30.84

Explanation: (0.21) (32) + (0.79) (28) = 28.84

7. Which among the following is always true for mass transfer to occur?
a) Difference in temperature
b) Difference in concentration
c) Difference in Pressure
d) Difference in chemical potential

Explanation: Mass transfer occurs to attain an equilibrium position or to minimize the energy of the system. Mass occur can occur even if there is no difference in concentration, pressure and temperature. Example: – A ball rolls down a slope to minimize its potential energy.

8. A binary mixture of oxygen and nitrogen with partial pressures in the ratio 0.21 and 0.79 is contained in a vessel at 300 K. If the total pressure of the mixture is 1 * 10 5 N/m2, find overall mass density
a) 4.156 kg/m3
b) 2.156 kg/m3
c) 1.156 kg/m3
d) 3.156 kg/m3

Explanation: For oxygen = 0.269 kg/m3 and for nitrogen = 0.887 kg/m3

9. For a binary mixture of species A and B, the mass average velocity is defined as
a) 2 pa Va + pb Vb/ p
b) pa Va + pb Vb/ p
c) pa Va + 2 pb Vb/ p
d) pa Va + pb Vb/ 2 p