640+ Mass Transfer Solved MCQs

These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .

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401.	Selectivity of the solvent used in solvent extraction should be
A.	1
B.	> 1
C.	< 1
D.	0
Answer» B. > 1

discuss

402.	The relative humidity of air decreases in-spite of an increase in the absolute humidity, when the
A.	Temperature rises
B.	Pressure rises
C.	Temperature falls
D.	Pressure falls
Answer» A. Temperature rises

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403.	The dew point of a saturated gas phase equals the __________ temperature.
A.	Gas
B.	Room
C.	Wet bulb
D.	None of these
Answer» A. Gas

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404.	The amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by
A.	Raising the temperature
B.	Lowering the total pressure
C.	Both (A) and (B)
D.	Neither (A) nor (B)
Answer» C. Both (A) and (B)

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405.	Priming in a distillation column
A.	Results from very low gas velocity
B.	Is desirable from point efficiency consideration
C.	Is characterised by the presence of foam throughout the space between trays
D.	Reduces the overall pressure drop
Answer» C. Is characterised by the presence of foam throughout the space between trays

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406.	Separation of a mixture of two gases by absorption in the liquid solvent depends upon the difference in their
A.	Viscosity
B.	Density
C.	Solubility
D.	Relative volatility
Answer» C. Solubility

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407.	The efficiency of a plate column will be maximum, when the flow is ideal __________ the plate.
A.	Across
B.	Above
C.	Both (A) & (B)
D.	Neither (A) nor (B)
Answer» C. Both (A) & (B)

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408.	__________ columns are used for liquid dispersion in a continuous gas phase.
A.	Packed
B.	Pulse
C.	Bubble cap
D.	Sieve plate
Answer» A. Packed

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409.	Pick out the wrong statement.
A.	When the concentration difference for the mass transfer becomes zero at the bottom of the gas absorption tower, then the upper end of the operating line touches the equilibrium curve
B.	The average distance between the operating line and equilibrium line is large, when the liquid- gas ratio is also large in case of a counter current gas absorption tower
C.	The operating line lies above the equilibrium curve in case of a gas desorber
D.	With decrease in the liquid flow rate for a fixed gas flow rate, the slope of the operating line decreases, in case of gas absorption process
Answer» C. The operating line lies above the equilibrium curve in case of a gas desorber

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410.	An alkaline solution is used to reduce the concentration of carbon dioxide in a stream from 10% to 0.1% by absorption with irreversible chemical reaction. The overall number of transfer units based on gas phase is:
A.	9.21
B.	4.605
C.	100
D.	0.001
Answer» B. 4.605

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411.	The overall mass transfer co-efficient for the absorption of SO2 in air with dilute NaOH solution can be increased substantially by
A.	Increasing the gas film co-efficient
B.	Increasing the liquid film co-efficient
C.	Increasing the total pressure
D.	Decreasing the total pressure
Answer» A. Increasing the gas film co-efficient

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412.	Air initially at 101. 3 kPa and 40°C and with a relative humidity of 50%, is cooled at constant pressure to 30°C. The cooled air has a
A.	Higher dew point
B.	Higher absolute (specific) humidity
C.	Higher relative humidity
D.	Higher wet bulb temperature
Answer» C. Higher relative humidity

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413.	When the psychometric ratio is __________ then the adiabatic saturation temperature and wet bulb temperature becomes equal.
A.	1
B.	< 1
C.	> 1
D.	∞
Answer» A. 1

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414.	With increase in the concentration of the adsorbate, the integral heat of adsorption
A.	Increases
B.	Decreases
C.	Remains unchanged
D.	May increase or decrease; depends on the type of adsorbate
Answer» B. Decreases

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415.	Use of raschig rings in place of crushed stones as packing in packed beds (other things being same)
A.	Increases pressure drop, increases surface area
B.	Increases pressure drop, decreases surface area
C.	Decreases pressure drop, increases surface area
D.	Decreases pressure drop, decreases surface area
Answer» C. Decreases pressure drop, increases surface area

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416.	A solid material shows case hardening properties while drying. Which of the following should be controlled to control the drying process?
A.	Flow rate of inlet air
B.	Relative humidity of outlet air
C.	Humidity of inlet air
D.	Temperature of the solid
Answer» D. Temperature of the solid

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417.	Fenske equation for determining the minimum number of theoretical stages in distillation column holds good, when the
A.	Relative volatility is reasonably constant
B.	Mixture (to be separated) shows negative deviation from ideality
C.	Mixture (to be separated) shows positive deviation from ideality
D.	Multi-component distillation is involved
Answer» A. Relative volatility is reasonably constant

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418.	When the __________ the relative humidity of air decreases, despite an increase in the absolute humidity.
A.	Temperature rises
B.	Pressure rises
C.	Temperature falls
D.	Pressure falls
Answer» A. Temperature rises

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419.	Pick out the wrong statement.
A.	Critical moisture content is not a property of the material itself
B.	A sharp increase in pressure drop gives an indication of the flooding in a distillation column
C.	Separation of components is not possible in liquid extraction, if selectivity is unity
D.	Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum
Answer» D. Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum

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420.	Detergent solution is dried to a powder in a
A.	Spray dryer
B.	Spouted bed dryer
C.	Tunnel dryer
D.	Pan open to atmosphere
Answer» A. Spray dryer

discuss

421.	Stefan's law describes the mass transfer by
A.	Diffusion
B.	Bulk flow
C.	Both 'a' & 'b'
D.	Neither 'a' nor 'b'
Answer» C. Both 'a' & 'b'

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422.	Which of the following equipments is not used in liquid-liquid extraction?
A.	Pachuka tank
B.	Agitated vessels
C.	Centrifugal extractors
D.	Packed towers
Answer» A. Pachuka tank

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423.	Flights in a rotary dryer are provided to
A.	Lift and shower the solids thus exposing it thoroughly to the drying action of the gas
B.	Reduce the residence time of solid
C.	Increase the residence time of the solid
D.	None of these
Answer» A. Lift and shower the solids thus exposing it thoroughly to the drying action of the gas

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424.	In a forced draft cooling tower, water is cooled from 95 to 80°F by exposure to air with a wet bulb temperature of 70°F. In this case, the
A.	Range is 15°F
B.	Approach is 10°F
C.	Both (A) & (B)
D.	Neither (A) nor (B)
Answer» C. Both (A) & (B)

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425.	To increase the absorption factor, (where, G = gas flow rate, S = solvent flow rate)
A.	Increase both 'G' and 'S'
B.	Decrease both 'G' and 'S'
C.	Increase 'S' and decrease 'G'
D.	Increase 'G' and decrease 'S'
Answer» C. Increase 'S' and decrease 'G'

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426.	The adiabatic saturation curve for a vapour-gas mixture is
A.	Straight line
B.	Slightly concave upward
C.	Slightly concave downward
D.	None of these
Answer» B. Slightly concave upward

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427.	For the case of flow of air past a wet bulb thermometer (air water vapour system), the approximate value of h2/ky .Cz is around
A.	0.60
B.	0.24
C.	1
D.	0.72
Answer» C. 1

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428.	The temperature to which a vapour gas mixture must be cooled (at varying humidity) to become saturated is called the __________ temperature.
A.	Dew point
B.	Wet bulb
C.	Dry bulb
D.	None of these
Answer» D. None of these

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429.	Absorption factor is defined as (where, S1 = slope of the operating line S2 = slope of the equilibrium curve)
A.	S2/S1
B.	S1/S2
C.	S1 - S2
D.	S1 × S2
Answer» B. S1/S2

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430.	At what value of reflux ratio, number of theoretical plates in a distillation column is minimum?
A.	0
B.	1
C.	∞
D.	< 1
Answer» C. ∞

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431.	Under conditions of flooding in packed tower, the gas pressure drop
A.	Decreases rapidly
B.	Increases rapidly
C.	Remain constant
D.	Is maximum
Answer» D. Is maximum

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432.	With increase in solvent rate, the number of transfer units, NtoG, for a fixed degree of absorption from a fixed amount of gas
A.	Increases
B.	Decreases
C.	Decreases linearly
D.	Remain unaffected
Answer» B. Decreases

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433.	Absorption accompanied with chemical reaction is exemplified by the absorption of
A.	Ammonia in water
B.	Benzol present in coke oven gas by wash oil
C.	SO2 in alkaline solution
D.	All (A), (B) and (C)
Answer» C. SO2 in alkaline solution

discuss

434.	For turbulent mass transfer in pipes, the Sherwood number depends on the Reynolds number as
A.	Re0.33
B.	Re0.53
C.	Re0.83
D.	Re
Answer» C. Re0.83

discuss

435.	In a counter-current liquid extractor
A.	Both liquids flow at fixed rate
B.	Both liquids can have any desired flow rate
C.	Only one of the liquids may be pumped at any desired rate
D.	Liquid’s flow rate depends upon the temperature and pressure
Answer» C. Only one of the liquids may be pumped at any desired rate

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436.	The vapour pressure exerted by the moisture contained in a wet solid depends upon the
A.	Nature of the moisture
B.	Temperature
C.	Nature of the solid
D.	All (A), (B) and (C)
Answer» D. All (A), (B) and (C)

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437.	In distillation, overhead product contains
A.	Only one component
B.	Two components
C.	Any number of components
D.	Only saturated liquid
Answer» C. Any number of components

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438.	Equilibrium-moisture curves of different solids
A.	Are different
B.	Are same
C.	Depend on the humidity of the gas
D.	None of these
Answer» A. Are different

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439.	The caking of crystals can be prevented by
A.	Maintaining high critical humidity
B.	Maintaining low critical humidity
C.	Coating the product with inert material
D.	Both (A) and (C)
Answer» D. Both (A) and (C)

discuss

440.	In McCabe-Thiele method of theoretical plate calculation for a distillation column, the operating lines of stripping and rectifying sections coincide with the diagonal at __________ reflux.
A.	Total
B.	Minimum
C.	Operating
D.	Maximum permissible
Answer» A. Total

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441.	Mass transfer co-efficient (K) and diffusivity (D) are related according to film theory as
A.	K ∝ D
B.	K ∝√D
C.	K ∝ D 1.5
D.	K ∝ D 2
Answer» A. K ∝ D

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442.	Steady state equimolal counter diffusion occurs in case of
A.	Leaching
B.	Absorption
C.	Binary phase distillation
D.	Liquid-liquid extraction
Answer» C. Binary phase distillation

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443.	On moving the feed line (q-line) from saturated liquid feed (vertical position) to saturated vapor feed (horizontal feed), if the slope of both the operating lines are to be increased, then it will result in
A.	Greater degree of separation with a fixed number of trays
B.	Increased reboiler load
C.	Increased reflux ratio
D.	None of these
Answer» C. Increased reflux ratio

discuss

444.	__________ is used as an 'entrainer' for the separation of acetic acid-water mixture by distillation.
A.	Furfural
B.	Benzol
C.	Butyl acetate
D.	Hexane
Answer» C. Butyl acetate

discuss

445.	Mass transfer rate between two fluid phases does not necessarily depend on the __________ of the two phases.
A.	Chemical properties
B.	Physical properties
C.	Degree of turbulence
D.	Interfacial area
Answer» A. Chemical properties

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446.	If mass diffusivity in a mixture is equal to the thermal diffusivity, then the Lewis number is
A.	0
B.	1
C.	< 1
D.	> 1
Answer» B. 1

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447.	Which of the following solutions will follow Raoult's law most closely?
A.	A solution of benzene, toluene and o-xylene
B.	35% solution of camphor in water
C.	35% solution of NH3 in water
D.	A solution of polar organic compounds (not of homologue of a series)
Answer» A. A solution of benzene, toluene and o-xylene

discuss

448.	For continuous drying of granular or crystalline material, the dryer used is the __________ dryer.
A.	Tunnel
B.	Tray
C.	Rotary
D.	None of these
Answer» C. Rotary

discuss

449.	Pick out the correct statement.
A.	In case of liquid-liquid extraction, no separation is possible, if the selectivity of the solvent used is unity
B.	With increase in temperature, the selectivity of the solvent used in solvent extraction decreases
C.	The selectivity of solvent used in solvent extraction is unity at the plait point
D.	All (A), (B) and (C)
Answer» D. All (A), (B) and (C)

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450.	__________ column is preferred to be used, when a high liquid hold up is required in a reactor for gas-liquid reaction.
A.	Packed
B.	Bubble
C.	Spray
D.	Tray
Answer» B. Bubble

discuss

640+ Mass Transfer Solved MCQs

Selectivity of the solvent used in solvent extraction should be

The relative humidity of air decreases in-spite of an increase in the absolute humidity, when the

The dew point of a saturated gas phase equals the __________ temperature.

The amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by

Priming in a distillation column

Separation of a mixture of two gases by absorption in the liquid solvent depends upon the difference in their

The efficiency of a plate column will be maximum, when the flow is ideal __________ the plate.

__________ columns are used for liquid dispersion in a continuous gas phase.

Pick out the wrong statement.

An alkaline solution is used to reduce the concentration of carbon dioxide in a stream from 10% to 0.1% by absorption with irreversible chemical reaction. The overall number of transfer units based on gas phase is:

The overall mass transfer co-efficient for the absorption of SO2 in air with dilute NaOH solution can be increased substantially by

Air initially at 101. 3 kPa and 40°C and with a relative humidity of 50%, is cooled at constant pressure to 30°C. The cooled air has a

When the psychometric ratio is __________ then the adiabatic saturation temperature and wet bulb temperature becomes equal.

With increase in the concentration of the adsorbate, the integral heat of adsorption

Use of raschig rings in place of crushed stones as packing in packed beds (other things being same)

A solid material shows case hardening properties while drying. Which of the following should be controlled to control the drying process?

Fenske equation for determining the minimum number of theoretical stages in distillation column holds good, when the

When the __________ the relative humidity of air decreases, despite an increase in the absolute humidity.

Pick out the wrong statement.

Detergent solution is dried to a powder in a

Stefan's law describes the mass transfer by

Which of the following equipments is not used in liquid-liquid extraction?

Flights in a rotary dryer are provided to

In a forced draft cooling tower, water is cooled from 95 to 80°F by exposure to air with a wet bulb temperature of 70°F. In this case, the

To increase the absorption factor, (where, G = gas flow rate, S = solvent flow rate)

The adiabatic saturation curve for a vapour-gas mixture is

For the case of flow of air past a wet bulb thermometer (air water vapour system), the approximate value of h2/ky .Cz is around

The temperature to which a vapour gas mixture must be cooled (at varying humidity) to become saturated is called the __________ temperature.

Absorption factor is defined as (where, S1 = slope of the operating line S2 = slope of the equilibrium curve)

At what value of reflux ratio, number of theoretical plates in a distillation column is minimum?

Under conditions of flooding in packed tower, the gas pressure drop

With increase in solvent rate, the number of transfer units, NtoG, for a fixed degree of absorption from a fixed amount of gas

Absorption accompanied with chemical reaction is exemplified by the absorption of

For turbulent mass transfer in pipes, the Sherwood number depends on the Reynolds number as

In a counter-current liquid extractor

The vapour pressure exerted by the moisture contained in a wet solid depends upon the

In distillation, overhead product contains

Equilibrium-moisture curves of different solids

The caking of crystals can be prevented by

In McCabe-Thiele method of theoretical plate calculation for a distillation column, the operating lines of stripping and rectifying sections coincide with the diagonal at __________ reflux.

Mass transfer co-efficient (K) and diffusivity (D) are related according to film theory as

Steady state equimolal counter diffusion occurs in case of

On moving the feed line (q-line) from saturated liquid feed (vertical position) to saturated vapor feed (horizontal feed), if the slope of both the operating lines are to be increased, then it will result in

__________ is used as an 'entrainer' for the separation of acetic acid-water mixture by distillation.

Mass transfer rate between two fluid phases does not necessarily depend on the __________ of the two phases.

If mass diffusivity in a mixture is equal to the thermal diffusivity, then the Lewis number is

Which of the following solutions will follow Raoult's law most closely?

For continuous drying of granular or crystalline material, the dryer used is the __________ dryer.

Pick out the correct statement.

__________ column is preferred to be used, when a high liquid hold up is required in a reactor for gas-liquid reaction.