# Mass Transfer Questions and Answers – Material Balance Concepts-Counter Current

This set of Mass Transfer Interview Questions & Answers focuses on “Material Balance Concepts-Counter Current”.

1. Relation between the slope of two operating line in the give figure.

a) Equal
b) Un equal
c) 1>2
d) 2>1

Explanation: There are parallel operating lines so the slope will be same.

2. Only small equipments are required for co-current process.
a) True
b) False

Explanation: Only for the counter current process, the mean driving force is large so small equipment is needed.

3. Find the concentration representation in the equilibrium distribution curve given below.

a) Mole ratio
b) Mass ratio
c) Mole fraction
d) None of the mentioned

Explanation: The operating line is a curve, so the representation must be in mole or mass fraction.

4. Find the slope of the operating line from the figure below.

If, Ls,Gs- non diffusing solvent
X,Y- Concentrations in mole ratio
x,y- concentration in mole fraction
a) Ls/Gs
b) –Ls/Gs
c) Gs/Ls
d) –Gs/Ls

Explanation: Gs(Y1)+Ls(X2)= Gs(Y2)+ls(X1)
Y1-Y2= Ls/Gs(X1-X2)
So the slope of the operating line is Ls/Gs.

5. Find the driving force at the point (P) in the equilibrium distribution curve given below.

a) Zero
b) Infinity
c) One
d) Greater than one

Explanation: Here, the operating line touches the equilibrium line the mass transfer rates becomes zero. So the driving force will be zero at the point P.
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6. The driving force line between the operating line and the equilibrium line depends on
a) Relative diffusion resistance
b) Relative mass resistance
c) Cumulative resistance
d) None of the mentioned

Explanation: As the driving force changes continuously at every point in a counter current process, the relative diffusion resistance is taken into consideration.

7. Removal of ammonia from the air with water is an example of a counter-current process.
a) True
b) False

Explanation: Here, the ammonia + air is sent through one side and water is sent through other end.

8. For Air-Water system Lewis Number equals to
a) Approx 1
b) 0
c) Infinity
d) 0 to 1

Explanation: For the air-water system the simultaneous heat and mass transfer takes place. Therefore the Schmidt number (Sc) and Prandtl number (Pr) become equal. Lewis number= (Sc/Pr) equals to 1.

Sanfoundry Global Education & Learning Series – Mass Transfer.