Free Mass Transfer Operations MCQs with Answers

• A. Enthalpy concentration method
• B. Ponchan-Savarit method
• C. McCabe-Thiele method
• D. Plate absorption column

Explanation: The McCabe-Thiele method uses the constant-molal-overflow assumption, allowing straight operating lines to be drawn on the x-y diagram.

• A. At very high liquid flow rate
• B. In towers packed randomly with crushed solids
• C. In dumped packing of regular units
• D. In towers packed with stacked packing

Explanation: Stacked packing tends to create preferential channels and poor liquid redistribution because the elements are arranged in continuous…

• A. Vapour pressure of component A to that of component B
• B. Vapour pressure of component A to the total pressure
• C. Vapour pressure of component A to the partial pressure of A
• D. Partial pressure of component A to the total pressure

Explanation: For an ideal liquid and vapour, Raoult's and Dalton's laws give relative volatility as \(\alpha=P_A^{sat}/P_B^{sat}\), the ratio of the…

• A. Low pressure drop
• B. High pressure drop
• C. Low velocity of the liquid
• D. High temperature

Explanation: Flooding occurs when the gas or vapour velocity becomes so high that it entrains liquid and prevents proper downward flow, producing a…

• A. Gilliland
• B. Stefan
• C. Toor and Marcello
• D. Fick

Explanation: The film-penetration model combines the ideas of a stagnant interfacial film and penetration by fluid elements, and is associated with…

• A. Stanton
• B. Sherwood
• C. None of these
• D. Peclet

Explanation: The product of Reynolds and Schmidt numbers is the mass-transfer Peclet number, \(Pe=Re\,Sc\), which compares convective transport with…

• A. Increases
• B. Decreases
• C. Remain same
• D. May increase or decrease; depends on system

Explanation: During constant-reflux batch distillation, the more volatile component is removed preferentially, so its concentration in the still…

• A. Decoction
• B. Percolation
• C. Elutriation or elution
• D. None of these

Explanation: When the soluble material is concentrated on the surface of an insoluble solid, the solvent mainly washes it away rather than dissolving…

• A. Distillation
• B. Evaporation
• C. Absorption
• D. Liquid extraction

Explanation: Acidification converts penicillin into a form that preferentially partitions into an immiscible organic solvent, so liquid-liquid…

• A. > 1
• B. 1
• C. < 1
• D. ≤ 1

Explanation: The absorption factor must exceed unity for the specified absorption to be feasible with a finite number of stages.

• A. Liquid-solid
• B. Fluid-solid
• C. Gas-solid
• D. Solid-solid

Explanation: Adsorption occurs when a solute from a fluid phase accumulates on a solid surface, so it is generally classified as a fluid-solid…

• A. Avoiding deposition on cooler surfaces
• B. Formation of nuclei
• C. Crystal growth
• D. All A., B. and C.

Explanation: Agitation keeps crystals suspended, improves heat and mass transfer, reduces deposition on cooled surfaces, and promotes controlled…

• A. Thermal diffusivity to mass diffusivity
• B. Mass diffusivity to momentum diffusivity
• C. Momentum diffusivity to thermal diffusivity
• D. None of these

Explanation: The Lewis number compares thermal diffusivity with mass diffusivity: Le = α/D.

• A. Sherwood
• B. Schmidt
• C. Peclet
• D. Stanton

Explanation: The Sherwood number, Sh = kL/D, compares convective mass transfer with molecular diffusion.

• A. Evaporator
• B. Distillation column
• C. Dryer
• D. Crystalliser

Explanation: A Cox chart gives vapour-pressure or boiling-point relationships for components and is used in estimating relative volatility for…

• A. √T and T3/2
• B. T and T3/2
• C. T3/2 and T
• D. T3/2 and √T

Explanation: Gas-phase binary diffusivity increases approximately as T raised to the 3/2 power at fixed pressure, while liquid diffusivity is commonly…

• A. At ambient temperature
• B. None of these
• C. In its vapor form
• D. At its boiling point

Explanation: Decoction is extraction using a solvent heated to its boiling point, commonly used to withdraw soluble constituents from solid materials.

• A. Pressure
• B. Concentration
• C. Thermal
• D. Forced

Explanation: Ordinary diffusion is caused by a concentration gradient, so it is also called concentration diffusion.

• A. Perforated tray
• B. Bubble cap
• C. Wetted wall
• D. Packed

Explanation: A wetted-wall tower has only a thin liquid film and no trays, packing, or bubbling resistance, so its gas-side pressure drop is the lowest…

• A. Selectivity
• B. Distribution co-efficient
• C. Both A. and B.
• D. Neither A. nor B.

Explanation: A useful extraction solvent should have high selectivity and a favourable distribution coefficient, not values below one.