Free Mass Transfer Operations MCQs with Answers

• A. Either A. or B.; depends on the solid
• B. More than
• C. Equal to
• D. Less than

Explanation: Bound moisture is held by the solid through adsorption or capillary forces, so it has a lower escaping tendency than free liquid.

• A. Agitation
• B. Temperature
• C. Particle size
• D. None of these

Explanation: Leaching rate is affected by agitation, temperature, and particle size: agitation improves contact, temperature changes diffusivity and…

• A. Mole ratio
• B. Partial pressure
• C. Mole fraction
• D. None of these

Explanation: For absorption, the operating relationship is linear when expressed using solute-free mole ratios, commonly written as Y versus X.

• A. Dynamic viscosity
• B. Kinematic viscosity
• C. Surface tension
• D. Pressure

Explanation: Mass diffusivity has dimensions of area per time, m²/s. Kinematic viscosity has the same dimensions, whereas dynamic viscosity, surface…

• A. Kc = Kp = Km
• B. Kc = Kp/RT = Km . RT/P
• C. Kc = Kp . RT = Km . RT/p
• D. None of these

Explanation: For an ideal gas, concentration is related to pressure by C = p/RT, while mole fraction is related by y = p/P.

• A. All A., B. & C.
• B. Velocity
• C. Temperature
• D. Humidity

Explanation: Constant drying conditions require the surrounding air properties that control drying to remain fixed, including temperature, humidity…

• A. Increases
• B. Decreases
• C. Remain same
• D. Either A. or B., depends on the system

Explanation: At a fixed temperature, adsorption generally increases with equilibrium pressure because more adsorbate molecules are available at the…

• A. Separation of the constituents is the most effective
• B. Amount of solvent required will be minimum
• C. No separation will occur
• D. Solvent flow rate should be very low

Explanation: Selectivity measures how preferentially the solvent extracts one solute over another.

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

Explanation: In film theory, the mass-transfer coefficient is approximately k = D/δ, where δ is the stagnant-film thickness, so it is directly…

• A. Podbielniak
• B. Scheibel
• C. Treybal
• D. None of these

Explanation: The Podbielniak extractor is a rotating centrifugal contactor that uses centrifugal force to contact and separate the two liquid phases.

• A. Maximum
• B. Minimum
• C. Infinite
• D. Zero

Explanation: At minimum reflux, the required reflux flow and hence the reboiler and condenser duties are minimized, so the operating cost is minimum.

• A. 0.54
• B. 1.04
• C. 1.24
• D. 1.94

Explanation: For equal drug volume, the initial dissolution rate is proportional to exposed surface area.

• A. Increases
• B. Decreases
• C. Remains unchanged
• D. Decreases exponentially

Explanation: For most partially miscible liquid pairs, increasing temperature increases mutual solubility by making mixing more favorable.

• A. D ∝ P0.5
• B. D ∝ 1/P
• C. D ∝ 1/P0.5
• D. D ∝ 1/P1.5

Explanation: Gas-phase diffusivity varies approximately inversely with total pressure because increasing pressure reduces the mean free path of…

• A. Yes
• B. Normally not; but is possible if infinite number of plates are put
• C. Never
• D. Yes; if the reflux ratio is maximum

Explanation: Plate efficiency is the actual separation achieved divided by the ideal equilibrium-stage separation, so it cannot exceed 100 percent.

• A. Decreased solute solubility
• B. Large minimum liquid to gas (L/G) ratio
• C. Large number of trays
• D. All A., B. and C.

Explanation: Heat evolution raises the liquid temperature and usually lowers solute solubility, reducing the absorption driving force.

• A. Winkelmann's
• B. Gilliland's
• C. Wetted wall column
• D. Wike's

Explanation: Winkelmann's method determines vapor diffusivity experimentally by observing the evaporation or movement of a liquid-vapor boundary in a…

• A. Small sizes
• B. Multi-component distillation
• C. High pressure operation
• D. Vacuum distillation

Explanation: Packed columns provide a large contact area with relatively low pressure drop, but their practical use in distillation is generally…

• A. Sieve plate
• B. Pulsed column
• C. Mixer-settler
• D. Bollman

Explanation: A pulsed column enhances mixing and mass transfer through repeated pulsations, making it suitable for liquid-liquid extraction of…

• A. Uranium from its ore
• B. Mustard oil from mustard seed
• C. Ammonia from coke oven gas
• D. Water from petrol

Explanation: Water can be removed from petrol by adsorption on materials such as silica gel or molecular sieves.