Engineering Questions with Answers - Multiple Choice Questions

# Separation Processes MCQ’s – Two Film Theory and Overall Mass transfer Coefficients

1 - Question

What results due to addition of surfactants?
a) Ease of diffusion
b) Interfacial mass transfer resistance
c) Ease of mass transfer
d) A cloud over the liquid interface
Explanation: The surfactants which reduce the surface tension results in Interfacial mass transfer resistance.

2 - Question

Which of the following is true about rate of mass transfer in gas?
a) NA = kp(pab-pai)
b) NA = kp(cab-cai)
c) NA = kc(pab-pai)
d) NA = kc(cab-cai)
Explanation: For diffusion in gas, partial pressure of the gas is considered.

3 - Question

Which of the following is true about rate of mass transfer in liquid?
a) NA = kp(pab-pai)
b) NA = kp(cab-cai)
c) NA = kc(pab-pai)
d) NA = kc(cab-cai)
Explanation: For mass transfer in liquid, molar concentration is considered

4 - Question

Which of the following is the incorrect form of Henry’s law?
a) pA=HAxA
b) pA = cA/HA
c) Xa=HAxA
d) YA = HAxA
Explanation: All are the correct forms of henry’s law except Xa=HAxA.

5 - Question

Which of the following is true about overall mass transfer coefficient KL?
a) KL =HA/kp +1/kc
b) 1/KL = HA/kp +1/kc
c) KL =1/HA kp +1/kc
d) 1/KL = HA/kp +kc
Explanation: Using henry’s law and slope point form in the graph we get 1/KL = HA/kp +1/kc.

6 - Question

What is the correct expression for overall mass transfer coesfficient based on mole fraction driving forces?
a) 1/Kx = 1/KAky + 1/kx
b) Kx = 1/KAky + 1/kx
c) 1/Kx = KA/ky + 1/kx
d) 1/Kx = 1/KAkx + 1/ky
Explanation: 1/Kx = 1/KAky + 1/kx is the correct representation of overall mass transfer coefficient.

7 - Question

What will be the overall mass transfer coefficient when the resistance by gas phase is negligible?
a) 1/Kx = 1/KAky + 1/kx
b) Kx = 1/KAky + 1/kx
c) 1/Kx = KA/ky + 1/kx
d) 1/Kx = 1/KAkx + 1/ky
Explanation: When the resistance by gas is negligible 1/KAky>>1/kx.

8 - Question

What are the correct SI units for kx, ky?
a) kmol/s-m
b) kmol/s-m2
c) mol/s-m2
d) kmol/s
Explanation: The SI units for kx and ky is kmol/s-m2.

9 - Question

Which of the following is true for mass transfer across liquid-liquid interface?
a) 1/Kx(2) = 1/KAkx(1) + 1/ky(2)
b) 1/Kx(2) = 1/KAky(2) + 1/kx(2)
c) 1/Kx(2) = 1/KAkx(1) + 1/kx(2)
d) 1/Kx(2) = 1/ky(1) + 1/kx(2
Explanation: For mass transfer across liquid-liquid interface 1/Kx(2) = 1/KAkx(1) + 1/kx(2) holds true.

10 - Question

What is the SI unit of kp?
a) kmol/s-m2-pa
b) kmol/s-m-kpa
c) kmol/m2-kpa
d) kmol/s-m2-kpa