Free Mass Transfer Operations MCQs with Answers

• A. Constant molal overflow
• B. All A., B. and C.
• C. Constant relative volatility
• D. Total reflux

Explanation: The Fenske relation gives the minimum number of stages at total reflux and is commonly applied with constant relative volatility and…

• A. Slope of the operating line in stripping section decreases
• B. Number of plates decreases very slowly first and then more and more rapidly
• C. Total cost first decreases and then increases
• D. Liquid flow increases while the vapor flow decreases for a system

Explanation: Increasing reflux reduces the number of stages required, but it increases internal flows and operating cost.

• A. Have low weight per unit volume
• B. Have large surface area per unit volume
• C. Have large free cross-section
• D. Hold up large amount of liquid in the packing

Explanation: Packing should provide high area and free space while remaining light and retaining only a small amount of liquid.

• A. Stanton number
• B. Peclet number
• C. Thermal diffusivity
• D. Momentum diffusivity

Explanation: The mass-transfer Stanton number is defined as Sh divided by Re Sc, or Sh/(Re Sc).

• A. Phase change of the solute as it dissolves in the solvent
• B. Diffusion of the solute through the solvent in the pores to the outside of the particle
• C. Diffusion of the solute from the solution in contact with the particle to the main bulk of the
• D. All A , B. & C.
• E. solution

Explanation: Solid-liquid extraction can involve solute dissolution, diffusion through the particle pores, and external diffusion from the particle…

• A. Degree of dispersion of one fluid in the other
• B. Interfacial surface exposed between the phases
• C. Both A. & B.
• D. None of these

Explanation: Dispersion affects the renewal and mixing of phases, while interfacial area determines how much contact surface is available for transfer.

• A. Temperature
• B. Pressure
• C. Both A. & B.
• D. Neither A. nor B.

Explanation: Gas diffusivity generally increases with temperature because molecular motion becomes faster, and decreases with pressure because…

• A. Temperature is less
• B. Mixing of steam with the material being vaporised is not so intimate as to result in equilibrium
• C. Total pressure is less
• D. condition
• E. Saturated steam is used for steam distillation

Explanation: In steam distillation, the steam and evaporated material usually do not contact long or intimately enough to reach vapour-liquid…

• A. Dry bulb
• B. Dew point
• C. Wet bulb
• D. None of these

Explanation: Wet-bulb temperature is reached when a small liquid sample evaporates into a large stream of unsaturated gas and the latent heat removed…

• A. Viscosity
• B. Vapor pressure
• C. Freezing point
• D. All A., B. & C.

Explanation: An absorption solvent should have low viscosity for rapid mass transfer, low vapour pressure to minimize solvent loss, and a low freezing…

• A. Temperature
• B. Viscosity of solvent
• C. Pressure
• D. Size of the solid

Explanation: Higher temperature generally increases solvent diffusivity and reduces viscosity, accelerating penetration of solvent into the solid and…

• A. Murphree efficiency > point efficiency
• B. Murphree efficiency = point efficiency
• C. Murphree efficiency < point efficiency
• D. Murphree efficiency ≠ point efficiency

Explanation: Murphree efficiency is an average efficiency over the tray, whereas point efficiency is local.

• A. The dimension of diffusivity is same as that of the
• B. Density
• C. Kinematic viscosity
• D. Molal concentration
• E. Velocity head

Explanation: Molecular diffusivity has dimensions of length squared per time, such as m²/s.

• A. Both A & B
• B. Viscosity
• C. Degree of ideality
• D. Neither A nor B

Explanation: Concentrated-solution diffusion is affected by non-ideality and by concentration-dependent viscosity, whereas dilute-solution relations…

• A. Number of plates is zero
• B. Number of plates is infinity
• C. Minimum number of the theoretical plates is required
• D. Separation is most efficient

Explanation: At minimum reflux, the operating line touches the equilibrium curve, creating a pinch point where an infinite number of theoretical stages…

• A. Mixer-settler extractor
• B. Packed extraction tower
• C. Pulsed extractor
• D. Centrifugal extractor

Explanation: A centrifugal extractor generates a strong artificial gravitational field, allowing rapid phase separation even when the density…

• A. Infinity
• B. Zero
• C. Unity
• D. Data insufficient

Explanation: At total reflux, all condensed overhead liquid is returned to the column and no distillate is withdrawn.

• A. P
• B. 1/P
• C. 1/√P
• D. √P

Explanation: For gases, molecular diffusivity is approximately inversely proportional to total pressure, expressed as D_AB ∝ 1/P.

• A. A pure component
• B. Partially miscible ternary system
• C. A ternary mixture
• D. A binary mixture

Explanation: Each side of a ternary triangular diagram corresponds to zero concentration of one component, leaving a binary mixture of the other two…

• A. Multi-component distillation
• B. Solid-liquid extraction
• C. Multi-component absorption with chemical reaction
• D. Liquid-liquid extraction

Explanation: The Thiele-Geddes method is a stage-by-stage calculation for multicomponent distillation, using component material balances and stage…