IndiaBIX Chemical Engineering: Mass Transfer Section 10

Question 1

Steam distillation is used for separation of high boiling
substances from non-volatile impurities.
volatile impurity from still higher boiling substances.
both (a) and (b).
neither (a) nor (b).

Answer 1

both (a) and (b).

Question 2

The feed to fractionating column is changed from saturated vapour to saturated liquid. If the separation and reflux ratio remains unchanged, the number of ideal stages will
increase
decrease
remains same
depend on saturated boiling point
may increase or decrease

Answer 2

increase

Question 3

Rose oil is extracted from rose leaves using __________ distillation.
high pressure
low pressure
extractive
steam

Answer 3

steam

Question 4

Hypersorption refers to a __________ process.
fixed bed absorption
moving bed absorption
fixed bed adsorption
moving bed adsorption

Answer 4

moving bed adsorption

Question 5

Which of the following is the correct ternery diagram for liquid-liquid extraction system comprising of two pairs partly soluble (e.g., chlorobenzene-water-methyl ethyl ketone system) ?

Answer 5

0

Question 6

Extraction of coffee from its seed is done by
liquid-liquid extraction.
leaching.
extractive distillation.
steam distillation.

Answer 6

leaching.

Question 7

In azeotropic mixture, the equilibrium vapour composition is
more than liquid composition.
less than liquid composition.
same as liquid composition.
independent of pressure.

Answer 7

same as liquid composition.

Question 8

With lapse of time, the overhead composition of light component in case of batch distillation with constant reflux
increases
decreases
remains same
may increase or decrease
depends on system.

Answer 8

decreases

Question 9

Lewis number, which is important in problems involving simultaneous heat and mass transfer, is the ratio of
mass diffusivity to momentum diffusivity.
thermal diffusivity to mass diffusivity.
momentum diffusivity to thermal diffusivity.
none of these.

Answer 9

thermal diffusivity to mass diffusivity.

Question 10

According to the film theory of mass transfer, the mass transfer co-efficient is proportional to (where, D = molecular diffusivity)
D
D^2
D^0.5
1/D

Answer 10

D

Question 11

Dry bulb temperature of the gas is __________ the wet bulb temperature.
less than
more than
equal to
none of these

Answer 11

more than

Question 12

Decoction refers to the use of solvent
at ambient temperature
at its boiling point
in its vapor form
none of these

Answer 12

at its boiling point

Question 13

Flash distillation is suitable for separating the constituents of a binary system, which
form minimum boiling azeotrope.
have very wide boiling points.
have very close boiling points.
form constant boiling azeotrope.

Answer 13

have very wide boiling points.

Question 14

The ratio of Murphree plate efficiency to point efficiency is 1 in a __________ flow model.
plug
perfectly mixed
both (a) & (b)
neither (a) nor (b)

Answer 14

perfectly mixed

Question 15

The rough value of diffusion co-efficient of water vapor into air at 25°C may be about __________ cm2/sec.
0.25
2.5
1.25
0.0025

Answer 15

0.25

Question 16

Flooding in a column results due to
high pressure drop
low pressure drop
low velocity of the liquid
high temperature

Answer 16

high pressure drop

Question 17

Which of the following gas-liquid contacting devices incurs the least pressure drop for a particular duty ?
Grid tray tower
Perforated tray tower
Wetted wall tower
Bubble cap tower

Answer 17

Wetted wall tower

Question 18

A liquid mixture contains 30% o-xylene, 60% p-xylene and 10%. m-xylene (all percentages in w/w). Which of the following statements would be true in respect of this mixture?
The mixture exhibits an azeotrope at 101.3 kPa.
The composition of the mixture, in percent by volume is: o-xylene 30, p-xylene 60. and m-xylene 10.
The composition of the mixture in mole percent is: o-xylene 30, p-xylene 60 and m-xyoene 10.
The mixture contain optical isomers.

Answer 18

The mixture exhibits an azeotrope at 101.3 kPa.

Question 19

Unsaturated air (with dry bulb temperature and dew point being 35°C and 18°C respectively) is passed through a water spray chamber maintained at 15°C. The air will be cooled
and humidified.
and dehumidified with increase in wet bulb temperature.
at the same relative humidity.
and dehumidified with decrease in wet bulb temperature.

Answer 19

and dehumidified with decrease in wet bulb temperature.

Question 20

The process employing desorption of the absorbed solute by a solvent is called
elution
osmosis
reverse osmosis
sublimation

Answer 20

elution

Question 21

If the overall efficiency and Murphree plate efficiency are equal, then both the equilibrium and operating lines are
straight
parallel
both (a) & (b)
neither (a) nor (b)

Answer 21

both (a) & (b)

Question 22

Which of the following operations does not involve leaching ?
Dissolving gold from ores.
Dissolving pharmaceutical products from bark or roots.
Dissolving sugar from the cells of the beet.
Removing nicotine from its water solution by kerosene.

Answer 22

Removing nicotine from its water solution by kerosene.

Question 23

The recovery of pencillin from the acidified fermentation broth is done by
distillation
evaporation
absorption
liquid extraction

Answer 23

liquid extraction

Question 24

Unit operation involved in the prilling of urea is
evaporation
drying
crystallisation
both (b) and (c)

Answer 24

both (b) and (c)

Question 25

Molecular seives are porous alumina. silica. synthetic zeolites crystals/metal alumino-silicates. none of these.

Answer 25

synthetic zeolites crystals/metal alumino-silicates.

Question 26

Calcium ammonium nitrate (a fertiliser) is dried in a __________ dryer. rotary vacuum tunnel tray

Answer 26

rotary

Question 27

A binary mixture of benzene and cyclohexane is separated by flash vaporisation extractive distillation solvent extraction ordinary distillation

Answer 27

extractive distillation

Question 28

Component A is diffusing in a medium B. The flux NA relative to a stationary point is equal to the flux due to molecular difusion, if mass transfer is accompanied by reaction. diffusion of A is in stagnant medium B. molecular mean free path is high. there is equimolar counter diffusion.

Answer 28

there is equimolar counter diffusion.

Question 29

Cox chart is useful in the design of distillation column evaporator dryer crystalliser

Answer 29

distillation column

Question 30

Dew point of an air-water vapor mixture decreases with decrease in pressure. at constant humidity & total pressure is fixed. corresponding to any point on the humidity chart is obtained by projecting a line through this point parallel to the temperature axis and to the saturation curve. all 'a', 'b' & 'c'.

Answer 30

all 'a', 'b' & 'c'.

Question 31

Can a cooling tower cool water below the wet bulb temperature of inlet air ? yes no yes but height of cooling tower will be prohibitively high. yes but the air flow rate should be excessively high.

Answer 31

no

Question 32

The solvent used in liquid-liquid extraction should have __________ less than one. selectivity distribution co-efficient both (a) and (b) neither (a) nor (b).

Answer 32

neither (a) nor (b).

Question 33

The suitable evaporator for concentration of foaming liquids is a __________ evaporator. long tube short tube vacuum falling film

Answer 33

long tube

Question 34

The ratio of Murphree plate efficiency to point efficiency is always > 1 in a __________ flow model. plug perfectly mixed both (a) & (b) neither (a) nor (b)

Answer 34

plug

Question 35

Tea percolation employs liquid-liquid extraction leaching absorption none of these

Answer 35

leaching

Question 36

Which of the following assumes constant molal vaporisation and overflow ? McCabe-Thiele method Ponchan-Savarit method Enthalpy concentration method Plate absorption column

Answer 36

McCabe-Thiele method

Question 37

Absorption factor, for a fixed degree of absorption from a fixed amount of gas should be 1 > 1 < 1 ≤ 1

Answer 37

> 1

Question 38

Selectivity of the solvent used in solvent extraction should be 1 > 1 < 1 0

Answer 38

> 1

Question 39

Pick out the wrong statement pertaining to leaching. Fine solids can not be leached in a Pachuka tank. Door classifier can be used for leaching of coarse solids. Vegetable seeds can be leached in either of Bollman extractor, Rotocel or Kennedy extractor. Very high temperature is not needed for the leaching of sugar beet.

Answer 39

Fine solids can not be leached in a Pachuka tank.

Question 40

Wet bulb and dry bulb temperatures becomes identical at __________ percent saturation curve. 100 50 78 none of these

Answer 40

100

Question 41

NSc/NPr is called the psychrometric ratio Lewis number Sherwood number Stantan number

Answer 41

Lewis number

Question 42

McCabe-Thiele method uses molal units for material and energy balance. uses weight fractions to express liquid and vapour composition. can use any type of units. is more accurate than Ponchan-Savarit method.

Answer 42

uses molal units for material and energy balance.

Question 43

The film penetration model of mass transfer was enunciated by Gilliland Toor and Marchello Stefan Fick

Answer 43

Toor and Marchello

Question 44

The most economical range of absorption factor is 0 to 0.5 0 to 3 1.25 to 2 5 to 15

Answer 44

1.25 to 2

Question 45

Channelling is most severe in towers packed with stacked packing. in towers packed randomly with crushed solids. in dumped packing of regular units. at very high liquid flow rate.

Answer 45

in towers packed with stacked packing.

Question 46

Out of two equilibrium curves, first one lies above the diagonal and the second lies below the diagonal in the x-y plot. It means that separation by distillation is not possible in the second case unless vacuum is applied. not possible in the second case unless high pressure is applied. more readily done in the second case compared to first one. none of these

Answer 46

more readily done in the second case compared to first one.

Question 47

ADDUCTS' and 'CLATHRATES' are used in case of extractive distillation. crystallisation. absorption. none of these.

Answer 47

crystallisation.

Question 48

Adsorption is an unit operation which generally involves __________ systems. liquid-solid gas-solid fluid-solid solid-solid

Answer 48

fluid-solid

Question 49

In case of __________ distillation, a solvent is added to alter the relative volatility of the mixture to be separated. molecular azeotropic extractive flash.

Answer 49

extractive

Question 50

Separation of the isotopes of helium for scientific investigations is done by reverse osmosis thermal diffusion leaching solvent extraction

Answer 50

thermal diffusion