IndiaBIX Chemical Engineering: Mass Transfer Section 3

Question 1

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
greater degree of separation with a fixed number of trays
increased reboiler load
increased reflux ratio
None of these.

Answer 1

increased reflux ratio

Question 2

__________ column is the most suitable for achieving the best performance for mass transfer operations involving liquid with dispersed solids.
Watted wall
Packed
Plate
Spray

Answer 2

Plate

Question 3

Deairation (removal of O2) of water is done by
rectification
absorption
ion-exchange
adsorption

Answer 3

ion-exchange

Question 4

Make up water is supplied during cooling tower operation to compensate for water losses due to
evaporation
blowdown
entrainment
all (a), (b)&(c)

Answer 4

all (a), (b)&amp(c)

Question 5

Pick out the wrong statement.
The mole fraction of solute is directly proportional to the molality of a ‘dilute’ solution.
For a non-reacting binary mixture of ideal gases, the partial pressure distribution of both components is nonlinear in the case of steady state unimolal unidirectional diffusion.
Azeotropes obey Raoult’s law at all temperature.
The relative volatility of a binary mixture at the azeotropic composition is 1.

Answer 5

Azeotropes obey Raoult’s law at all temperature.

Question 6

A minimum boiling azeotrope is exemplified by
toluene-benzene
acetone-carbon disulphide
water-isobutyl alcohol
none of these

Answer 6

acetone-carbon disulphide

Question 7

Which of the following solutions will follow Raoult’s law most closely ?
A solution of benzene, toluene and oxylene.
35% solution of camphor in water.
35% solution of NH3 in water.
A solution of polar organic compounds (not of homologs of a series).

Answer 7

A solution of benzene, toluene and oxylene.

Question 8

Use of raschig rings in place of crushed stones as packing in packed beds (other things being same)
increases pressure drop, increases surface area.
increases pressure drop, decreases surface area.
decreases pressure drop, increases surface area.
decreases pressure drop, decreases surface area.

Answer 8

decreases pressure drop, increases surface area.

Question 9

Critical humidity of a solid salt means the humidity
above which it will always become damp.
below which it will always stay dry.
both (a) and (b).
above Which it will always become dry and below which it will always stay damp.

Answer 9

both (a) and (b).

Question 10

The assumption made in Elis method in distillation is that enthalpy concentration lines of vapor and liquid are
parallel
straight
both parallel and straight
neither parallel nor straight

Answer 10

both parallel and straight

Question 11

As complete saturation of an adsorbent is approached, the differential heat of adsrop-tion approaches
that of normal condensation.
integral heat of adsorption.
zero.
none of these.

Answer 11

that of normal condensation.

Question 12

Absorption with chemical reaction’ is involved in the removal of
carbon dioxide from gaseous stream using alkaline solution.
benzol from coke oven gas using solar oil/wash oil.
ammonia from coke oven gas using refrigerated water.
tar from coke oven gas in primary gas coolers using chilled water.

Answer 12

carbon dioxide from gaseous stream using alkaline solution.

Question 13

The-relative volatility for separation of a non-ideal binary mixture by distillation should be
0
1
> 1
< 1

Answer 13

> 1

Question 14

Pick out the wrong statement:
Reboiler is not used in open steam distillation.
The separation of solutes of different molecular sizes in a liquid solution by use of a suitable membrane is called dialysis.
Freeze drying is used for the drying of fish.
Fenske-Underwood equation is used for calculating theoretical number of plates in a distillation column at normal operating reflux condition.

Answer 14

Fenske-Underwood equation is used for calculating theoretical number of plates in a distillation column at normal operating reflux condition.

Question 15

In paper industry, paper is dried in a __________ dryer.
tunnel
heated cylinder
conveyor
festoon

Answer 15

heated cylinder

Question 16

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

Answer 16

Dehydration of ethyl alcohol is most economically done by molecular distillation at very high vacuum.

Question 17

Only small amount of evaporation of water produces large cooling effects because of its
large latent heat
low viscosity
small latent heat
none of these

Answer 17

large latent heat

Question 18

The most common packing used in industrial operations is __________ rings.
raschig
lessing
cross-partition
single spiral

Answer 18

raschig

Question 19

When the feed to a distillation column is a saturated liquid, slope of the feed line is
zero
unity
infinity
none of these

Answer 19

infinity

Question 20

Leaching of sugar from sugar beets is done by
hot water
hexane
dilute H2SO4
lime water

Answer 20

hot water

Question 21

Absorption factor method is used to calculate the number of ideal stages, when
operating line lies above the equilibrium line.
operating line lies below the equilibrium line.
both operating and equilibrium lines are parallel.
pressure drop in the column is very high.

Answer 21

both operating and equilibrium lines are parallel.

Question 22

Flights in a rotary dryer are provided to
lift and shower the solids thus exposing it thoroughly to the drying action of the gas.
reduce the residence time of solid.
increase the residence time of the solid.
none of these.

Answer 22

lift and shower the solids thus exposing it thoroughly to the drying action of the gas.

Question 23

If f = moles of vapour present per mole of feed, then the slope of feed line is (Mcabe-Thiele method)
(1-f)/f
-(f-1)/f
-1/f
-f/(1-f)

Answer 23

• 1/f

Question 24

If the solubilities of different components (in a liquid-liquid extraction system) increase with rise in temperature, then the temperature above which they dissolve completely is known as the critical solution temperature (CST or consolute temperature). If solubilities increase with decrease in temperature, then CST is the temperature below which they dissolve completely. If a binary system has no critical solution temperature, it implies that
the system comprises of partially mis-cible liquids.
the system comprises of miscible liquids.
the system comprises of an azeotrope.
on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.

Answer 24

on heating, a vapor phase will appear ; while on cooling, a solid phase will appear.

Question 25

The rate of mass transfer is not dependent upon the
degree of dispersion of one fluid in the other.
interfacial surface exposed between the phases.
both (a) & (b).
none of these.

Answer 25

none of these.

Question 26

At equilibrium the concentration of water in vapour phase (C)in kg/m3 of air space and the amount of water (m) adsorbed per kg of dry silica gel are related by, C = 0.0667m. To maintain dry conditions in a room of air space 100m3 containing 2.2 kg of water vapour initially, 10 kg of dry silica gel is kept in the room. The fraction of initial water remaining in the air space after a long time (during which the temperature is maintained constant) is
0.0
0.2
0.4
1.0

Answer 26

0.4

Question 27

Dry bulb temperature of unsaturated air is more than its __________ temperature.
dew point
wet bulb
both ‘a’ & ‘b’
neither ‘a’ nor ‘b’

Answer 27

both ‘a’ & ‘b’

Question 28

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
0.60
0.24
1
0.72

Answer 28

1

Question 29

The reciprocal of stripping factor is termed as
selectivity index
relative volatility
absorption factor
Murphree efficiency

Answer 29

absorption factor

Question 30

Ponchan-Savarit method analyses the fractional equipment based on
enthalpy balance only.
material balance only.
both enthalpy and material balances.
the assumption of constant molaloverflow.

Answer 30

both enthalpy and material balances.

Question 31

The binary diffusivity in gases at atmospheric conditions is about
10-9 cm/sec
10-1 cm2/sec
10-3 sec/cm
10-4 cm2/sec2

Answer 31

10-1 cm2/sec

Question 32

Percentage saturation is __________ the relative saturation.
always smaller than
always greater than
not related to
none of these

Answer 32

always smaller than

Question 33

In case of a desorber (stripper), the
operating line always lies above the equilibrium curve.
operating line always lies below the equilibrium curve.
temperature remains unaffected.
temperature always increases.

Answer 33

operating line always lies below the equilibrium curve.

Question 34

What is the reflux ratio at total reflux ?
Zero
Infinity
Unity
Data insufficient

Answer 34

Infinity

Question 35

Under conditions of flooding in packed tower, the gas pressure drop
decreases rapidly
increases rapidly
remains constant
is maximum

Answer 35

is maximum

Question 36

For achieving rapid drying rate in a spray dryer, the diameter of the particles in the feed should be in the range of __________ microns (1 mm = 1000 microns).
1-5
10-60
200-300
> 500

Answer 36

10-60

Question 37

For absorbing a sparingly soluble gas in a liquid
gas side mass transfer co-efficient should be increased.
liquid side mass transfer co-efficient should be increased.
liquid side mass transfer co-efficient should be decreased.
mass transfer co-efficient must be kept constant.

Answer 37

liquid side mass transfer co-efficient should be increased.

Question 38

Channelling in a packed tower results from the
high pressure drop
maldistribution of liquid
non-uniformity of packing
both (b) and (c)

Answer 38

both (b) and (c)

Question 39

The change in enthalpy per unit weight of adsorbed gas when adsorbed on gas free or “outgassed” adsorbent to from a definite concentration of adsorbate is called its
integral heat of adsorption.
heat of wetting.
differential heat of adsorption.
heat of normal condensation.

Answer 39

integral heat of adsorption.

Question 40

The minimum number of theoretical plates is required for achieving a given separation in distillation column with
no reflux
total reflux
zero reflux ratio
minimum reflux ratio

Answer 40

total reflux

Question 41

A good solvent used for absorption should not have very high
viscosity
vapor pressure
freezing point
all (a), (b) & (c)

Answer 41

all (a), (b) & (c)

Question 42

In a counter-current liquid extractor
both liquids flow at fixed rate.
both liquids can have any desired flow rate.
only one of the liquids may be pumped at any desired rate.
liquid’s flow rate depends upon the temperature and pressure.

Answer 42

only one of the liquids may be pumped at any desired rate.

Question 43

Which of the following is an undesirable property for an absorbing solvent ?
Low vapour pressure
Low velocity
Low freezing point
None of these

Answer 43

None of these

Question 44

The wetted wall tower is used to determine
individual mass transfer co-efficient (M.T.C.) in gaseous system.
M.T.C. of individual components in a liquid-liquid system.
M.T.C. of liquid in liquid-gas system.
the overall M.T.C. of the system.

Answer 44

individual mass transfer co-efficient (M.T.C.) in gaseous system.

Question 45

Weight of 1 m3 of humid air as compared to 1 m3 of dry air, under the same conditions, is
less
more
same
unpredictable

Answer 45

less

Question 46

Positive deviation from Raoult’s law means a mixture whose total pressure is
greater than that computed for ideality.
less than that computed for ideality.
less than the sum of the vapour pressure of the components.
none of these.

Answer 46

greater than that computed for ideality.

Question 47

With increase in gas rate, the number of transfer units, NtoG, for a fixed degree of absorption by a fixed amount of solvent
increases
decreases
decreases linearly
remains unaffected

Answer 47

increases

Question 48

Schmidt number is given by
µ / ρDAB
Re.Pe
Sh x Pe
Re/Pe

Answer 48

µ / ρDAB

Question 49

The caking of crystals can be prevented by
maintaining high critical humidity.
maintaining low critical humidity.
coating the product with inert material.
both (a) and (c)

Answer 49

both (a) and (c)

Question 50

Prandtl number for water at 20°C is about
7
70
0.7
150.

Answer 50

7