## Multiple Choice Questions (MCQ) and Answers on Mass Transfer

**Question 1 : In distillation columns, the number of bubble caps per tray primarily depends upon the**

- allowable liquid velocity.
- allowable gas velocity.
- allowable gas and liquid velocities.
- feed composition.

**Answer : 3**

**Question 2 : In distillation, overhead product contains**

- only one component
- two components
- any number of components
- only saturated liquid

**Answer : 3**

**Question 3 : With increase in pressure, the relative volatility for a binary system**

- increases.
- decreases.
- remains same.
- either (1) or (2), depends on the system.

**Answer : 3**

**Question 4 : Low viscosity absorbent is preferred for reasons of**

- rapid absorption rates and good heat transfer characteristics.
- improved flooding characteristics.
- low pressure drop on pumping.
- all (a), (b) and (c).

**Answer : 4**

**Question 5 : Mass transfer co-efficient ( K) and diffusivity (D) are related according to film theory as**

*K*∝*D**K*∝

$\sqrt{D}$*K*∝*D*^{1.5}*K*∝*D*^{2}

**Answer : 1**

**Question 6 : Which of the following liquid-vapor contacting devices provides maximum contact surface area for a particular duty ?**

- Sieve plate column
- Bubble cap column
- Randomly packed column
- Wetted wall column

**Answer : 4**

**Question 7 : The equipment frequently used for adiabatic humidification-cooling operation with recirculating liquid is**

- natural draft cooling tower
- induced draft cooling tower
- spray chamber
- none of these

**Answer : 3**

**Question 8 : Chemisorption (chemical adsorption) is**

- same as “Van der Waals” adsorption.
- characterised by adsorption of heat.
- an irreversible phenomenon.
- a reversible phenomenon.

**Answer : 3**

**Question 9 : The rate of solid-liquid extraction is limited by the**

- phase change of the solute as it dissolves in the solvent.
- diffusion of the solute through the solvent in the pores to the outside of the particle.
- diffusion of the solute from the solution in contact with the particle to the main bulk of the solution.
- all ‘1’, ‘2’ & ‘3’.

**Answer : 4**

**Question 10 : Raoult’s law applies to the**

- all liquid solutions
- non-ideal solution only.
- non-volatile solute.
- solvents.

**Answer : 4**

**Question 11 : Make up water is required in a cooling tower to replace the water lost by**

- evaporation
- drift
- blowdown and leakage
- all (a), (b) and (c)

**Answer : 4**

**Question 12 : Which of the following quantities need not be fixed before starting the design of a co-current absorber ?**

- Heat gain or loss
- Flow rate of entering liquid
- Flow rate of gas
- None of these

**Answer : 2**

**Question 13 : Mass transfer co-efficient of liquid is**

- affected more by temperature than that for gases.
- affected much less by temperature than that for gases.
- not affected by the temperature.
- none of these.

**Answer : 1**

**Question 14 : Absorption accompanied with chemical reaction is exemplified by the absorption of**

- ammonia in water.
- benzol present in coke oven gas by wash oil.
- SO
_{2}in alkaline solution. - all (a), (b) and (c).

**Answer : 3**

**Question 15 : Which of the following unit operations makes use of Thiele-Geddes equation ?**

- Liquid-liquid extraction
- Solid-liquid extraction
- Multicomponent absorption with chemical reaction
- Multicomponent distillation.

**Answer : 4**

**Question 16 : As the reflux ratio in a distillation coloumn is increased from the minimum, the**

- slope of the operating line in stripping section decreases.
- number of plates decreases very slowly first and then more and more rapidly.
- total cost first decreases and then increases.
- liquid flow increases while the vapor flow decreases for a system.

**Answer : 3**

**Question 17 : Absorption factor is defined as (where, S_{1} = slope of the operating line S_{2} = slope of the equilibrium curve)**

*S*/_{2}*S*_{1}*S*/_{1}*S*_{2}*S*–_{1}*S*_{2}*S*x_{1}*S*_{2}

**Answer : 2**

**Question 18 : A plait point is the point on the solubility curve, where the tie line reduces to a point. What is the number of plait point for a ternery system containing twopairs of partially miscible liquids ?**

- 0
- 1
- 2
- 3

**Answer : 1**

**Question 19 : Which of the following remains constant during sensible cooling process ?**

- Specific humidity
- Partial pressure of vapour
- Both (1) and (2)
- Neither (1) nor (2)

**Answer : 3**

**Question 20 : Physical absorption is**

- an irreversible phenomenon.
- a reversible phenomenon.
- accompanied by evolution of heat.
- both (2) and (3)

**Answer : 4**

**Question 21 : The mass diffusivity, the thermal diffusivity and the eddy momentum diffusivity are same for, N_{Pr} = N_{Sc} = __________**

- 1
- 0.5
- 10
- 0

**Answer : 1**

**Question 22 :Dew point of a gas-vapour mixture**

- increases with temperature rise.
- decreases with temperature rise.
- decreases with decrease in pressure.
- increases with increase in pressure.

**Answer : 3**

**Question 23 : In a packed absorption tower, if the equilibrium and operating lines are both straight lines, then the ratio, HETP/HTU _{OG} __________ the absorption factor.**

- increases with increase in
- is one at unity value of
- both (1) and (2)
- neither (1) nor (2)

**Answer : 3**

**Question 24 : Which of the following plays an important role in problems of simultaneous heat and mass transfer ?**

- Lewis number
- Schmidt number
- Prandtl number
- Sherwood number

**Answer : 1**

**Question 25 : In case of an absorber, the operating**

- line always lies above the equilibrium curve.
- line always lies below the equilibrium curve.
- line can be either above or below the equilibrium curve.
- velocity is more than the loading velocity.

**Answer : 1**

**Question 26 : Relative humidity is the ratio of the**

- partial pressure of the vapour to the vapour pressure of the liquid at room temperature.
- partial pressure of the vapour to the vapour pressure of the liquid at gas temperature.
- actual humidity to saturation humidity.
- none of these

**Answer : 2**

**Question 27 : In batch distillation with constant reflux, overhead product composition __________ with time.**

- increases
- decreases
- does not vary
- may increase on decrease, depends on the system.

**Answer : 2**

**Question 28 : Psychrometry deals with the properties of gas-vapor mixture. Humidity can be determined by the measurement of the __________ of a fibre.**

- electrical resistance
- thermal conductivity
- strength
- none of these.

**Answer : 1**

**Question 29 : Heat in BTU necessary to increase the temperature of 1 lb of gas and its accompanying vapour by 1°F is called the**

- latent heat
- humid heat
- specific heat
- sensible heat

**Answer : 3**

**Question 30 : To increase the absorption factor, (where, G = gas flow rate, S = solvent flow rate)**

- increase both ‘
*G*‘ and ‘*S*‘. - decrease both ‘
*G*‘ and ‘*S*‘. - increase ‘
*S*‘ and decrease ‘*G*‘. - increase ‘
*G*‘ and decrease ‘*S*‘

**Answer : 3**

**Question 31 : Drying operation under vacuum is carried out to**

- dry those materials which have very high unbound mositure content.
- reduce drying temperature.
- increase drying temperature.
- dry materials having high bound moisture content.

**Answer : 2**

**Question 32 : 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**

- higher dew point
- higher absolute (specific) humidity.
- higher relative humidity
- higher wet bulb temperature.

**Answer : 3**

**Question 33 : Separation of two or more components of a liquid solution can not be achieved by**

- fractional crystallisation
- liquid extraction
- absorption
- evaporation

**Answer : 3**

**Question 34 : Stefan’s law describes the mass transfer by**

- diffusion
- bulk flow
- both ‘a’ & ‘b’
- neither ‘a’ nor ‘b’

**Answer : 3**

**Question 35 : At minimum reflux ratio for a given separation**

- number of plates is zero.
- number of plates is infinity.
- minimum number of the theoretical plates is required.
- separation is most efficient.

**Answer : 2**

**Question 36 : Pick out the correct statement.**

- In case of liquid-liquid extraction, no separation is possible, if the selectivity of the solvent used is unity.
- With increase in temperature, the selectivity of the solvent used in solvent extraction decreases.
- The selectivity of solvent used in solvent extraction is unity at the plait point.
- all (1), (2) and (3).

**Answer : 4**

**Question 37 : __________ columns are used for liquid dispersion in a continuous gas phase.**

- Packed
- Pulse
- Bubble cap
- Sieve plate

**Answer : 1**

**Question 38 : Overall efficiency of the distillation column is**

- the ratio of number of ideal plates to actual plates.
- the ratio of number of actual plates to ideal plates.
- same as the Murphree efficiency.
- always more than the point efficiency.

**Answer : 1**

**Question 39 : On addition of solute in the solvent, the __________ of the solution decreases.**

- boiling point
- freezing point
- vapour pressure
- both (2) and (3)

**Answer : 4**

**Question 40 : Which is the controlling factor for a drum drier?**

- Diffusion
- Heat transfer
- Both (1) and (2)
- Neither (1) nor (2)

**Answer : 2**

**Question 41 : Total reflux in a distillation operation requires minimum**

- reboiler load
- number of plates
- condenser load
- all (1), (2) and (3)

**Answer : 2**

**Question 42 : The amount of steam required per unit quantity of distillate in case of steam distillation will be reduced by**

- raising the temperature.
- lowering the total pressure.
- both (1) and (2)
- neither (1) nor (2).

**Answer : 3**

**Question 43 : The difference of wet bulb temperature and adiabatic saturation temperature of unsaturated mixture of any system is**

- +ve
- -ve
- zero
- none of these

**Answer : 1**

**Question 44 : Fenske’s equation for determining the minimum number of theoretical stages in distillation column holds good, when the**

- relative volatility is reasonably constant.
- mixture (to be separated) shows negative deviation from ideality.
- mixture (to be separated) shows positive deviation from ideality.
- multicomponent distillation is involved.

**Answer : 1**

**Question 45 : When the temperature and humidity of air is low, we usually use __________ draft cooling tower.**

- natural
- forced
- induced
- none of these

**Answer : 1**

**Question 46 : Mass transfer rate between two fluid phases does not necessarily depend on the __________ of the two phases.**

- chemical properties
- physical properties
- degree of turbulence
- interfacial area

**Answer : 1**

**Question 47 : In a solution containing 0.30 Kg mole of solute and 600 kg of solvent, the molality is**

- 0.50
- 0.60
- 2
- 1

**Answer : 1**

**Question 48 : Fenske equation determines the**

- maximum number of ideal plates.
- height of the distillation column.
- minimum number of theoretical plates.
- optimum reflux ratio.

**Answer : 3**

**Question 49 : The term “cooling range” in a cooling tower refers to the difference in the temperature of**

- cold water leaving the tower and the wet bulb temperature of the surrounding air.
- hot water entering the tower and the wet bulb temperature of the surrounding air.
- hot water entering the tower and the cooled water leaving the tower.
- none of these

**Answer : 3**

**Question 50 : Which of the following is the most suitable for extraction in a system having very low density difference ?**

- Mixer-settler extractor
- Centrifugal extractor
- Pulsed extractor
- Packed extraction tower

**Answer : 2**