Mass Transfer MCQs

Option A: Liquid-liquid extraction

Option B: Solid-liquid extraction

Option C: Multi-component absorption with chemical reaction

Option D: Multi-component distillation

Correct Answer: Multi-component distillation ✔

Option A: 0

Option B: 1

Option C: > 1

Option D: < 1

Correct Answer: 1 ✔

Option A: X/(X + 1)

Option B: X/(1 – X)

Option C: (1 + X)/X

Option D: (1 – X)/X

Correct Answer: X/(X + 1) ✔

Option A: Water has a high latent heat of evaporation

Option B: Lewis number is close to unity

Option C: They are always equal under all circumstances

Option D: Solubility of the components of air in water is very small

Correct Answer: Water has a high latent heat of evaporation ✔

Option A: Ri = Re/(1 – Re)

Option B: Ri = (1 – Re)/Re

Option C: Ri = Re

Option D: Ri = Re/(1 + Re)

Correct Answer: Ri = Re ✔

Option A: Fractional crystallisation

Option B: Liquid extraction

Option C: Absorption

Option D: Evaporation

Correct Answer: Absorption ✔

Option A: Extracting solvent is cheaply & abundantly available

Option B: One of the liquid components is heat sensitive

Option C: Viscosity of liquid components is very high

Option D: One of the liquid components has very high affinity towards the solvent

Correct Answer: One of the liquid components has very high affinity towards the solvent ✔

Option A: Increases

Option B: Decreases

Option C: Remains unchanged

Option D: Depends on relative volatility

Correct Answer: Decreases ✔

Option A: Separation of uranium oxide from its ore by H2SO4 in a Pachuca tank

Option B: Separation of sugar from sugar beet by hot water

Option C: Dissolution of tannin out of tree barks by water

Option D: Recovery of vegetable oils from seeds

Correct Answer: Separation of uranium oxide from its ore by H2SO4 in a Pachuca tank ✔

Option A: Increases

Option B: Decreases

Option C: Remains same

Option D: Either A. or B., depends on the system

Correct Answer: Decreases ✔

Option A: The binary diffusivity in liquids is of the order of 10-5 cm2/sec

Option B: Molecular diffusion in solid is much faster than that in liquids

Option C: Particles movement from higher concentration to lower concentration takes place in diffusion

Option D: According to Poiseuille’s law, the permeability decreases with increase in temperature for

Correct Answer: Molecular diffusion in solid is much faster than that in liquids ✔

Option A: In case of induced draft cooling tower, the fan is placed at the top of the tower

Option B: Effectiveness of forced draft cooling tower is reduced by the recirculation of the humid and

Option C: A natural draft cooling tower is recommended to be used, when the air humidity is low and air

Option D: Effectiveness of a mechanical draft cooling tower is reduced with increase in air wet-bulb

Correct Answer: D. Effectiveness of a mechanical draft cooling tower is reduced with increase in air wet-bulb
temperature ✔

Option A: Change in barometric pressure does not affect the relative humidity

Option B: In case of a packed tower, the operating velocity is about half of the flooding velocity,

Option C: ‘Elution’ means the desorption of the adsorbed solute by a solvent

Option D: The equilibrium moisture content of the solid can be reduced by increasing the absolute

Correct Answer: D. The equilibrium moisture content of the solid can be reduced by increasing the absolute
humidity ✔

Option A: A horizontal line on the humidity chart indicates the temperature changes at constant molal

Option B: When water is cooled from 80 to 70°C by exposure to the air with a wet bulb temperature of

Option C: For unsaturated air-water vapor mixture at atmospheric conditions, the wet bulb temperature

Option D: Relative saturation of unsaturated mixture of water vapor & air cannot be increased by either

Correct Answer: D. Relative saturation of unsaturated mixture of water vapor & air cannot be increased by either
reducing the mixture temperature or by increasing the total pressure ✔

Option A: The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are the same

Option B: 1 Nm3 of dry air is lighter than 1Nm3 of humid air

Option C: The Lewis number of a mixture is unity, when the thermal diffusivity is equal to the mass

Option D: An Azeotropic mixture of two liquids has boiling point higher than either of them, when it

Correct Answer: 1 Nm3 of dry air is lighter than 1Nm3 of humid air ✔

Option A: Higher hold up of the solid in the rotary dryer results in better exposure of the solids to the gas

Option B: The ‘Hatta number’ is important in problems involving gas absorption without chemical

Option C: For a non-reacting binary mixture of ideal gases, the partial pressure distribution of both

Option D: Total reflux in case of distillation operation requires infinite number of plates for a binary

Correct Answer: C. For a non-reacting binary mixture of ideal gases, the partial pressure distribution of both
components is linear in the case of steady state equimolal counter-diffusion ✔

Option A: Constant pressure distillation cannot separate an Azeotropic mixture

Option B: Relative volatility of a binary mixture changes appreciably with the minor change in

Option C: The relative volatility of a binary mixture at Azeotropic composition is unity

Option D: Flash distillation is practised on wide spread scale in petroleum refinery

Correct Answer: B. Relative volatility of a binary mixture changes appreciably with the minor change in
temperature ✔

Option A: Ponchan-Savarit method is more accurate than McCabe-Thiele method to determine the

Option B: A sharp decrease in pressure drop is an indication of flooding in a distillation coloumn

Option C: Solvent used in extractive distillation should be of high volatility

Option D: Flash distillation is suitable for separating components which have very close boiling

Correct Answer: A. Ponchan-Savarit method is more accurate than McCabe-Thiele method to determine the
number of theoretical stages required for the separation of non-ideal binary system by
distillation ✔

Option A: Dialysis process is used for the production of fresh water from brine

Option B: Electrodialysis is used in the manufacture of NaOH

Option C: Electrodialysis is used for the refining/purification of petrol

Option D: Both B. and C.

Correct Answer: Electrodialysis is used in the manufacture of NaOH ✔

Option A: The slope of the stripping line is always less than unity

Option B: For a given separation in a binary distillation column, with increase in reflux ratio (above the

Option C: In Ponchon-Savarit method of no. of theoretical plate determination, the stripping and

Option D: Kremser-Brown-Souder’s equation is used to calculate the efficiency of a plate tower

Correct Answer: C. In Ponchon-Savarit method of no. of theoretical plate determination, the stripping and
rectifying operating lines are vertical at total reflux ✔

Option A: Flights (located in the inside shell of rotary dryer) lift the material being dried and shower it

Option B: Hold up of a rotary drier is defined as the fraction of the dryer volume occupied by the solid at

Option C: Rotary dryer is suitable for drying sticky material

Option D: Recommended peripheral speed of a rotary drier is in the range of 10 to 30 metres/minute

Correct Answer: Rotary dryer is suitable for drying sticky material ✔

Option A: With decrease in feed temperature, the number of plates required for binary distillation

Option B: The extraction per unit of total height for a short packed column is more effective than for a

Option C: Natural draft cooling towers are made of ferroconcrete and its cross-section is wider at the

Option D: Vander wall adsorption is also called chemisorption

Correct Answer: Vander wall adsorption is also called chemisorption ✔

Option A: For identical gas flow rates, less pressure drop occurs through a plate tower than through a

Option B: Plate column can handle greater liquid loads without flooding than packed column, but the

Option C: For the same duty, plate columns weigh less than packed columns

Option D: All A., B. and C.

Correct Answer: D. All A., B. and C. ✔

Option A: Fine solids cannot be leached in a Pachuca tank

Option B: Door classifier can be used for leaching of coarse solids

Option C: Vegetable seeds can be leached in either of Bollman extractor, Rotocel or Kennedy extractor

Option D: Very high temperature is not needed for the leaching of sugar beet

Correct Answer: Fine solids cannot be leached in a Pachuca tank ✔

Option A: Bound moisture is removed during constant rate drying period

Option B: Free moisture is removed during falling rate drying period

Option C: The sum of free moisture and equilibrium moisture in a solid is called the critical moisture

Option D: The driving force for mass transfer in a wet solid is its free moisture content

Correct Answer: The driving force for mass transfer in a wet solid is its free moisture content ✔

Option A: Packed towers are preferred for vacuum operation, because the pressure drop through the

Option B: Packed towers are preferred over plate towers for handling corrosive and foamy liquids

Option C: Diameter of randomly packed tower is normally more than 1.2 metres

Option D: Due to uneven supply and improper distribution of liquid, problem of channelling, loading &

Correct Answer: Diameter of randomly packed tower is normally more than 1.2 metres ✔

Option A: Different solids have different equilibrium moisture curves

Option B: Total condenser or reboiler is considered equivalent to one theoretical plate in McCabe-Thiele

Option C: Heat removal load on cooler remains constant, even with increase of the reflux ratio in a

Option D: Even a forced draft cooling tower cannot cool water below the wet bulb temperature

Correct Answer: C. Heat removal load on cooler remains constant, even with increase of the reflux ratio in a
distillation column ✔

Option A: When the concentration difference for the mass transfer becomes zero at the bottom of the gas

Option B: The average distance between the operating line and equilibrium line is large, when the liquidgas

Option C: The operating line lies above the equilibrium curve in case of a gas desorber

Option D: With decrease in the liquid flow rate for a fixed gas flow rate, the slope of the operating line

Correct Answer: The operating line lies above the equilibrium curve in case of a gas desorber ✔

Option A: In case of liquid-liquid extraction, no separation is possible, if the selectivity of the solvent

Option B: With increase in temperature, the selectivity of the solvent used in solvent extraction

Option C: The selectivity of solvent used in solvent extraction is unity at the plait point

Option D: All A., B. and C.

Correct Answer: D. All A., B. and C. ✔

Option A: In the McCabe-Thiele diagram for binary distillation, vertical feed line represents saturated

Option B: In small columns, local efficiency is larger than Murphree efficiency; in large columns local

Option C: For Laminar flow over a plate of length L, the local mass transfer co-efficient at a distance L

Option D: The concentration and hydrodynamic boundary layers over a flat plate are of equal thickness,

Correct Answer: C. For Laminar flow over a plate of length L, the local mass transfer co-efficient at a distance L
from the leading edge is 1.5 × 10-2m/s. Then the average mass transfer co-efficient for the
plate is 2 × 10-2m/s ✔

Option A: Cellulose acetate membranes are used in dialysis process

Option B: Elutriation process refers to when the soluble material is largely concentrated on the surface of

Option C: ‘Cascade’ means a group of stages interconnected so that various streams flow from one to

Option D: Zirconia probe is used for the humidity measurement

Correct Answer: Zirconia probe is used for the humidity measurement ✔

Option A: The operating line always lies above the equilibrium solubility curve in case of a single

Option B: The operating line always lies below the equilibrium solubility curve in case of a single

Option C: The operating pressure in solvent extraction system should be below vapor pressures of all

Option D: The solubility of a particular gas in ideal solution in any solvent is always the same

Correct Answer: C. The operating pressure in solvent extraction system should be below vapor pressures of all
components ✔

Option A: Critical moisture content is not a property of the material itself

Option B: A sharp increase in pressure drop gives an indication of the flooding in a distillation column

Option C: Separation of components is not possible in liquid extraction, if selectivity is unity

Option D: Dehydration of ethyl alcohol is most economically done by molecular distillation at very high

Correct Answer: D. Dehydration of ethyl alcohol is most economically done by molecular distillation at very high
vacuum ✔

Option A: Diffusivity decreases with increase in temperature

Option B: Diffusivity increases with increase in molecular weight

Option C: Diffusivity increases with the size of the individual molecule

Option D: None of these

Correct Answer: None of these ✔

Option A: Increases

Option B: Decreases

Option C: Remains same

Option D: Either A. or B., depends on the system

Correct Answer: Decreases ✔

Option A: Bone charcoal

Option B: Wood charcoal

Option C: Silica gel

Option D: Activated clay

Correct Answer: Bone charcoal ✔

Option A: High pressure drop

Option B: Maldistribution of liquid

Option C: Non-uniformity of packing

Option D: Both B. and C.

Correct Answer: D. Both B. and C. ✔

Option A: T1-Dew point temp; T2-Dry bulb temp; T3-Wet bulb temp

Option B: T1-Dew point temp; T2-Wet bulb temp; T3-Dry bulb temp

Option C: T1-Wet bulb temp; T2-Dry bulb temp; T3-Dew point temp

Option D: T1-Dry bulb temp; T2-Wet bulb temp; T3-Dew point temp

Correct Answer: T1-Dry bulb temp; T2-Wet bulb temp; T3-Dew point temp ✔

Option A: 1

Option B: > 1

Option C: < 1

Option D: 0.5

Correct Answer: 1 ✔

Option A: Sieve plate column

Option B: Bubble cap column

Option C: Randomly packed column

Option D: Wetted wall column

Correct Answer: Wetted wall column ✔

Option A: Festoon

Option B: Cylinder

Option C: Conveyor

Option D: Tunnel

Correct Answer: Conveyor ✔

Option A: Enthalpy balance only

Option B: Material balance only

Option C: Both enthalpy and material balances

Option D: The assumption of constant molal-overflow

Correct Answer: Both enthalpy and material balances ✔

Option A: Flooding

Option B: Gas viscosity

Option C: Liquid density

Option D: Liquid hold up

Correct Answer: Flooding ✔

Option A: Decreases in winter

Option B: Increases in winter

Option C: Increases in summer

Option D: None of these

Correct Answer: Increases in winter ✔

Option A: 0

Option B: 1

Option C: 2

Option D: 3

Correct Answer: 0 ✔

Option A: Form a low boiling azeotrope with one of the constituents of the mixture

Option B: Form a new azeotrope of low relative volatility with one of the constituents of the mixture

Option C: Have high latent heat of vaporisation

Option D: Have high viscosity to provide high tray efficiency

Correct Answer: Form a low boiling azeotrope with one of the constituents of the mixture ✔

Option A: Operating line lies above the equilibrium line

Option B: Operating line lies below the equilibrium line

Option C: Both operating and equilibrium lines are parallel

Option D: Pressure drop in the column is very high

Correct Answer: Both operating and equilibrium lines are parallel ✔

Option A: Bubble-cap column

Option B: Sieve-plate column

Option C: Packed column (stacked)

Option D: Randomly packed column

Correct Answer: Packed column (stacked) ✔

Option A: Sensible heat changes are negligible compared with latent heat changes

Option B: Molar latent heats of all components are equal

Option C: Heat of mixing is negligible

Option D: None of these

Correct Answer: None of these ✔

Option A: Water-alcohol

Option B: Methyl alcohol-acetone

Option C: Butyl acetate-water

Option D: None of these

Correct Answer: None of these ✔

Option A: Carbon dioxide from gaseous stream using alkaline solution

Option B: Benzol from coke oven gas using solar oil/wash oil

Option C: Ammonia from coke oven gas using refrigerated water

Option D: Tar from coke oven gas in primary gas coolers using chilled water

Correct Answer: Carbon dioxide from gaseous stream using alkaline solution ✔

Option A: Packed column (with stacked packing)

Option B: Packed column (with dumped packing)

Option C: Bubble plate column

Option D: Pulse column

Correct Answer: Packed column (with stacked packing) ✔

Option A: Centrifugal

Option B: Packed

Option C: Plate

Option D: None of these

Correct Answer: Centrifugal ✔

Option A: Always lower than

Option B: Always higher than

Option C: Same as

Option D: Dependent on the system; can be either lower or higher than

Correct Answer: Always lower than ✔

Option A: Boiling point

Option B: Freezing point

Option C: Vapour pressure

Option D: Both B. and C.

Correct Answer: D. Both B. and C. ✔

Option A: Wetted wall

Option B: Packed

Option C: Plate

Option D: Spray

Correct Answer: Plate ✔

Option A: Agitated vessels

Option B: Bubble cap tray towers

Option C: Perforated sieve tray towers

Option D: Spray towers

Correct Answer: Spray towers ✔

Option A: [xD/(RD + 1)], [RD/(RD + 1)]

Option B: [RD/(RD + 1)], [xD/(xD + 1)]

Option C: [xD/(RD + 1)], [(RD + 1)/RD]

Option D: None of these

Correct Answer: [RD/(RD + 1)], [xD/(xD + 1)] ✔

Option A: Agitated vessel

Option B: Sieve tray column

Option C: Bubble cap column

Option D: Packed tower

Correct Answer: Agitated vessel ✔

Option A: Maximum number of ideal plates

Option B: Height of the distillation column

Option C: Minimum number of theoretical plates

Option D: Optimum reflux ratio

Correct Answer: Minimum number of theoretical plates ✔

Option A: μ/ρDAB

Option B: Re × Pe

Option C: Sh × Pe

Option D: Re/Pe

Correct Answer: μ/ρDAB ✔

Option A: Higbie

Option B: Fick

Option C: Ergun

Option D: Levenspiel

Correct Answer: Higbie ✔

Option A: Provides poorer contact between the fluids

Option B: Gives lower pressure drop

Option C: Both A. and B.

Option D: Gives higher pressure drop

Correct Answer: C. Both A. and B. ✔

Option A: Incurs smaller pressure drop

Option B: Allows installation of cooling coils

Option C: Is less costly when built in large sizes/diameters

Option D: Is more suitable, if suspended solids are present in fluid streams

Correct Answer: Incurs smaller pressure drop ✔

Option A: All liquid solutions

Option B: Non-ideal solution only

Option C: Non-volatile solute

Option D: Solvents

Correct Answer: Solvents ✔

Option A: Low vapour pressure

Option B: Low velocity

Option C: Low freezing point

Option D: None of these

Correct Answer: None of these ✔

Option A: Leaching

Option B: Adsorption

Option C: Steam distillation

Option D: Multi-component absorption

Correct Answer: Adsorption ✔

Option A: Mixer-settler extractor

Option B: Rotating-disc contactor

Option C: Pulsed column extractor

Option D: Bollman extractor

Correct Answer: Pulsed column extractor ✔

Option A: Line always lies above the equilibrium curve

Option B: Line always lies below the equilibrium curve

Option C: Line can be either above or below the equilibrium curve

Option D: Velocity is more than the loading velocity

Correct Answer: Line always lies above the equilibrium curve ✔

Option A: Tunnel

Option B: Tray

Option C: Rotary

Option D: None of these

Correct Answer: Rotary ✔

A. 0
B. 1
C. 1

Correct Answer: 1 ✔

Option A: Furfural

Option B: Benzol

Option C: Butyl acetate

Option D: Hexane

Correct Answer: Butyl acetate ✔

Option A: Leaching

Option B: Absorption

Option C: Binary phase distillation

Option D: Liquid-liquid extraction

Correct Answer: Binary phase distillation ✔

Option A: Total

Option B: Minimum

Option C: Operating

Option D: Maximum permissible

Correct Answer: Total ✔

Option A: Are different

Option B: Are same

Option C: Depend on the humidity of the gas

Option D: None of these

Correct Answer: Are different ✔

Option A: Nature of the moisture

Option B: Temperature

Option C: Nature of the solid

Option D: All A., B. and C.

Correct Answer: D. All A., B. and C. ✔

Option A: Re0.33

Option B: Re0.53

Option C: Re0.83

Option D: Re

Correct Answer: Re0.83 ✔

Option A: Increases

Option B: Decreases

Option C: Decreases linearly

Option D: Remain unaffected

Correct Answer: Decreases ✔

Option A: 0

Option B: 1

Option C: ∞

Option D: < 1

Correct Answer: ∞ ✔

Option A: Dew point

Option B: Wet bulb

Option C: Dry bulb

Option D: None of these

Correct Answer: None of these ✔

Option A: Straight line

Option B: Slightly concave upward

Option C: Slightly concave downward

Option D: None of these

Correct Answer: Slightly concave upward ✔

Option A: Lift and shower the solids thus exposing it thoroughly to the drying action of the gas

Option B: Reduce the residence time of solid

Option C: Increase the residence time of the solid

Option D: None of these

Correct Answer: Lift and shower the solids thus exposing it thoroughly to the drying action of the gas ✔

Option A: Diffusion

Option B: Bulk flow

Option C: Both A. & B.

Option D: Neither A. nor B.

Correct Answer: C. Both A. & B. ✔

Option A: Relative volatility is reasonably constant

Option B: Mixture (to be separated) shows negative deviation from ideality

Option C: Mixture (to be separated) shows positive deviation from ideality

Option D: Multi-component distillation is involved

Correct Answer: Relative volatility is reasonably constant ✔

Option A: Increases pressure drop, increases surface area

Option B: Increases pressure drop, decreases surface area

Option C: Decreases pressure drop, increases surface area

Option D: Decreases pressure drop, decreases surface area

Correct Answer: Decreases pressure drop, increases surface area ✔

A. 1
B. 1
D. ∞

Correct Answer: 1 ✔

Option A: Increasing the gas film co-efficient

Option B: Increasing the liquid film co-efficient

Option C: Increasing the total pressure

Option D: Decreasing the total pressure

Correct Answer: Increasing the gas film co-efficient ✔

Option A: 0.01

Option B: 0.1

Option C: 10-5 to 10-6

Option D: > 1

Correct Answer: 10-5 to 10-6 ✔

Option A: Transfer of molecules from low concentration to high concentration region

Option B: Thermal energy of the molecules

Option C: Activation energy of the molecules

Option D: Potential energy of the molecules

Correct Answer: Thermal energy of the molecules ✔

Option A: Newtonian liquids

Option B: Non-Newtonian liquids

Option C: Ideal gases

Option D: Real gases

Correct Answer: Ideal gases ✔

Option A: Differential distillation equation

Option B: For NtoG in absorption for dilute mixture

Option C: Slope of q-line in McCabe-Thiele method

Option D: For relative volatility

Correct Answer: Differential distillation equation ✔

Option A: Evaporation

Option B: Drift

Option C: Blowdown and leakage

Option D: All A., B. and C.

Correct Answer: D. All A., B. and C. ✔

Option A: Straight

Option B: Parallel

Option C: Both A. & B.

Option D: Neither A. nor B.

Correct Answer: C. Both A. & B. ✔

Option A: Operating line always lies above the equilibrium curve

Option B: Operating line always lies below the equilibrium curve

Option C: Temperature remains unaffected

Option D: Temperature always increases

Correct Answer: Operating line always lies below the equilibrium curve ✔

Option A: 1

Option B: < 1

Option C: > 1

Option D: 0.5

Correct Answer: 1 ✔

Option A: Hot water

Option B: Hexane

Option C: Lime water

Option D: Dilute H2SO4 (hot)

Correct Answer: Hot water ✔

Option A: The system comprises of partially miscible liquids

Option B: The system comprises of miscible liquids

Option C: The system comprises of an azeotrope

Option D: On heating, a vapor phase will appear; while on cooling, a solid phase will appear

Correct Answer: On heating, a vapor phase will appear; while on cooling, a solid phase will appear ✔

Option A: Packed

Option B: Bubble

Option C: Spray

Option D: Tray

Correct Answer: Bubble ✔

Option A: Gas film

Option B: Liquid film

Option C: Liquid-gas interface

Option D: None of these

Correct Answer: Liquid film ✔

Option A: Liquid

Option B: Gas

Option C: Both A. & B.

Option D: Neither A. nor B.

Correct Answer: Gas ✔