Free Mass Transfer Operations MCQs with Answers

• A. Used for multi-component systems like crude refining
• B. Same as differential distillation
• C. Same as simple distillation
• D. Most useful for handling binary systems

Explanation: Flash distillation is a single-stage equilibrium separation in which part of a feed vaporises suddenly, and it is especially useful for…

• A. The partial pressure of water vapour increases
• B. The relative humidity decreases
• C. The relative humidity increases
• D. The specific humidity decreases

Explanation: At constant pressure without adding moisture, the water-vapour partial pressure and humidity ratio remain approximately constant, while…

• A. Penetration
• B. Film
• C. Surface renewal
• D. None of these

Explanation: Danckwerts proposed the surface-renewal theory, which treats turbulent eddies as continually replacing elements of liquid at the…

• A. Decoction
• B. Dissolution
• C. Agitation and settling
• D. Percolation

Explanation: Percolation is leaching by passing the solvent through a bed of coarse solid particles or lumps.

• A. Avoid thermal decomposition of a component
• B. Reduce the number of plates
• C. Increase the efficiency of separation
• D. Increase the total pressure of distillation

Explanation: Steam distillation lowers the boiling temperature by combining vapour pressures, allowing heat-sensitive substances to distil below their…

• A. KG = 1/KG + m/KL
• B. 1/KG = 1/KG + m/KL
• C. 1/KG = 1/KL + m/KG
• D. KG = 1/KL + m/KG

Explanation: For gas-film and liquid-film resistances in series, the overall gas-phase resistance is 1/KG = 1/kG + m/kL, where m is the…

• A. Flash
• B. Differential
• C. Equilibrium
• D. Molecular

Explanation: The Rayleigh equation is obtained from an unsteady material balance on a still and therefore applies to differential, or batch…

• A. 1
• B. 2
• C. 3
• D. 4

Explanation: Under the standard simplified absorption-process formulation with one solute transferred between two phases, three independent process…

• A. Cost
• B. Availability
• C. Toxicity
• D. Selectivity

Explanation: The separating agent must preferentially alter the relative volatility of the components being separated, so selectivity is the key…

• A. Is computed from the slope of the upper operating line that is tangent to the equilibrium curve
• B. Is computed from the intercept of the operating line
• C. Cannot be computed
• D. Is the optimum reflux ratio

Explanation: At minimum reflux, the operating line reaches a limiting pinch, commonly where it is tangent to the equilibrium curve, and its slope…

• A. K ∝D
• B. K ∝√D
• C. K ∝D1.5
• D. K ∝D2

Explanation: Penetration theory gives a transient diffusion-layer thickness proportional to the square root of Dt, so the mass-transfer coefficient…

• A. Packed towers
• B. Plate towers
• C. Wetted wall columns
• D. Spray towers

Explanation: Wetted-wall columns are primarily used to study gas-liquid mass transfer and are not standard contacting equipment for liquid-liquid…

• A. Only vapor phase follows Raoult's law
• B. Only liquid phase obeys Dalton's law
• C. Liquid phase obeys Dalton's law and vapor phase obeys Raoult's law
• D. Vapor phase obeys Dalton's law and liquid phase obeys Raoult's law

Explanation: For an ideal liquid solution, Raoult's law gives each component's partial pressure as xᵢPᵢ⁰, while Dalton's law relates partial pressure…

• A. Surface renewal
• B. Film
• C. Penetration
• D. None of these

Explanation: The film theory is the usual engineering basis for estimating mass-transfer coefficients by assuming a thin stagnant film controls…

• A. Increased diffusivity
• B. Decreased viscosity of liquid
• C. Both A. and B.
• D. Neither A. nor B.

Explanation: Higher temperature generally increases molecular diffusivity and lowers liquid viscosity, reducing resistance to solute movement during…

• A. 1
• B. 0
• C. 2
• D. 3

Explanation: A binary distillation system has two independent variables when pressure is allowed to vary.

• A. Unbound
• B. Critical
• C. Free
• D. Bound

Explanation: Unbound, or free, moisture has a vapour pressure equal to that of the pure liquid at the same temperature and is relatively easy to…

• A. Heat of wetting
• B. Differential heat of adsorption
• C. Integral heat of adsorption
• D. None of these

Explanation: Differential heat of adsorption is the enthalpy change for adsorbing an infinitesimal amount of gas on an adsorbent that already has a…

• A. Semi-batch
• B. Batch
• C. Continuous
• D. Cooling (adiabatic)-cum-evaporation

Explanation: A Swenson-Walker crystalliser is a continuous trough-type crystalliser in which slurry moves continuously over cooled surfaces.

• A. Bollman extractor
• B. Plate type extraction column
• C. Packed extraction column
• D. Rotating disc extractor

Explanation: Petrol desulphurisation by solvent extraction uses a rotating disc extractor, which provides repeated liquid-liquid contact and dispersion…