Mass transfer quiz


Mass transfer quiz


1.Diffusivity of gases at atmospheric pressure in cm2/s is in the range of 
a. less than 1                                     b. greater than 1
c. greater than 10                               d. greater than 100 


2. Diffusivity of liquids in cm2/s is of the order of 
a. 0.1                    b. 0.01                  c. 10                           d. 1 x 10-5 

3.Diffusivity of a gas varies with temperature and pressure according to the relation 
a. DμT1.5/P
b. DμT/P1.5
c. DμT1.5/P
d. none of the above 


4.Diffusivity of liquids can be estimated by 
a. Hirschfelder-Bird-Spotz equation    b. Gilliland equation
c. Lewis relation                                   d. Wilke–Chang equation 


5. Diffusivity of liquids varies with temperature according to the relation
a. DμT1.75                 b. DμT0.75                 c. Dμ                      d. Dμ T1.5

6. Molecular diffusion is due to 
a. thermal motion of the molecule
b. potential energy of the molecules
c. activation energy of the molecules
d. none of these 


7. Mass transfer coefficient is defined as 
a. Flux =(coefficient) / (concentration difference)
b. Flux =(coefficient) (concentration difference)
c. Flux =(concentration difference) / (coefficient)
d. none of these 


8. The ratio of mass flux for diffusion of A through non-diffusing B to the mass flux for equimolar counter-diffusion is 
a. greater than one
b. less than one
c. equal to one
d. information insufficient 


9. The mass transfer coefficients, kand kare related according to the relation 
a. k= kG
b. kYBM = kGPBM 
c. k/ P = k/ P2
d. All of these. 

10.According to the film theory, the mass transfer coefficient, kl, and diffusivity are related as 
a. klμD0.5                  b. klμDc. kμ D0.67              d. klμD-1

11.Which of the following theories predicts that kμ 0.67?
a. Penetration theory                b. Surface renewal theory 
c. Boundary layer theory          d. None of these. 

12. Corresponding to Prandtl number in heat transfer, the dimensionless group in mass transfer is 
a. Reynolds number                 b. Sherwood number 
c. Peclet number                      d. Schmidt number. 

13. Schmidt number is a ratio of 
a. momentum diffusivity to mass diffusivity
b. thermal diffusivity to mass diffusivity
c. thermal diffusivity to momentum diffusivity
d. None of these. 


14. Sherwood number is a ratio of 
a. Flow velocity to diffusion velocity
b. Convective flux to diffusive flux
c. either (a) or (b)
d. neither (a) nor (b) 


15. For mass transfer of a solute A present in a dilute mixture of A and B, the term PBM tends to 
a. total pressure P
b. zero
c. one
d. infinity 


16. Corresponding to Nusselt number in heat transfer, the dimensionless group in mass transfer is 
a. Peclet number
b. Knudsen number
c. Prandtl number
d. Sherwood number 


17. Stanton number for mass transfer is defined as 
a. Sc / (Sh.Re)                b. Re / (Sc.Sh)
c. (Re.Sh) / Sc                d. Sh / (Re.Sc) 


18. Which of the following analogies gives St = f / 2? 
a. Reynolds analogy
b. Prandtl analogy
c. Chilton–Colburn analogy
d. none of these 


19. According to Danckwerts surface renewal theory, the mass transfer coefficient, kl’ is given by 
a. DAB/S
b. (D
AB / S)0.5 
c. (DAB )0.5
d. (DAB .S)0.5

20. "S" in Danckwerts surface renewal theory is 
a. total surface renewed per unit time
b. surface area available for mass transfer
c. fraction of the surface renewed per unit time
d. none of these
21. Which of the following models is a steady state model? 
a. film model
b. penetration model
c. surface renewal model
d. all (a), (b) and (c) 


22. According to the penetration theory, the average mass transfer coefficient kL,av is given by 
a.     pt/DAB
b.     (t / DAB)0.5 
c.     (DAB t) #9; 
d.     2 (DAB t)0.5

23. For a certain mass transfer process, k= 1 x 10 -- 3 cm / s and DAB = 1 x 10 ---5 cm/s. The film thickness in cm is then 
a. 0.1cm
b. 0.01cm
c. 0.001cm

d. more information will be required for calculation of film thickness. 

24. Schmidt number for gases is of the order of 
a. 1
b. 10
c. 100
d. 1000 


25. Schmidt number for liquids is of the order of 
a. 0.1
b. 1
c. 10
d. 1000 


26. For evaporation from a spherical naphthalene ball in a stagnant medium, Sherwood number is equal to 
a. 0.5
b. 2
c. 20
d. 200 


27. According to film theory the mass transfer coefficient is proportional to 
a. D
b. D

c. D0.5 
d. 1/D 

28. The Knudsen diffusivity is dependent on 
a. molecular veloctiy only
b. the pore radius of the catalyst
c. the molecular mean free path only
d. the molecular velocity and pore radius of the catalyst 


29. A gaseous solute having mass diffusivity equal to 0.5 cm/s diffuses into a porous solid having a porosity of 0.5 and a tortuosity of 2. The effective diffusivity in the porous solid is 
a. 0.25 cm2/s
b. 0.5 cm
2/s
c. 1 cm
2/s
d. 0.125 cm
2/s 

30. Knudsen diffusion occurs when the ratio of mean free path to the pore diameter is 
a. much greater than one
b. much less than one
c. equal to one
d. none of these 


31. In Knudsen diffusion 
a. molecule – molecule collision is important
b. molecule – pore wall collision is important
c. both (a) and (b) are important
d. neither (a) nor (b) is important 


32. The term permeability is defined as 
a. permeability=solubility x diffusivity
b. permeability=solubility / diffusivity
c. permeability=diffusivity / solubility 

d. permeability=diffusivity / (solubility)

33. Knudsen diffusivity is 
a. directly proportional to total pressure
b. inversely proportional to total pressure
c. independent of total pressure
d. directly proportional to the square root of total pressure 


34. Gas separating membranes operate at 
a. a high pressure
b. a high pressure differential
c. both (a) and (b)
d. neither (a) nor (b) 


35. For absorption of NHfrom a dilute NH– air mixture in water, 
a. only gas side resistance is important
b. only liquid side resistance is important
c. both gas and liquid side resistances are equally important
d. gas side resistance is relatively more important than the liquid side resistance 


36. For absorption of benzene from a coal gas in wash oil, the major resistance to mass transfer comes from the 
a. gas side
b. liquid side
c. both gas and liquid side 


37. Rate of absorption of a sparingly soluble gas in a liquid can be increased by 
a. increasing the gas side mass transfer coefficient
b. decreasing the gas side mass transfer coefficient
c. increasing the liquid side mass transfer coefficient
d. decreasing the liquid side mass transfer coefficient 


38. The equilibrium relation for distribution of a solute between a gas and liquid phase is given by y = mx (at a particular temperature). If kand kare individual gas and liquid phase mass transfer coefficients, respectively, the overall gas phase mass transfer coefficient is given by the relation 
a.    1 / K= 1 / k+ m / k
b.    1 / K= m / k+ 1 / k
c.    1 / K= 1 / mk+ 1 / k
d.    1 / K= 1 / k+ 1 / mk

39. At a particular temperature the equilibrium relation for distribution of a solute between a gas and a liquid phase is given by p = HC. If kand kare, respectively, the gas and liquid phase mass 
transfer coefficients, the overall liquid phase mass transfer coefficient is given by the relation 
a.    1 / K= 1 / k+ H / k
b.    1 / K= 1 / Hk+ 1 / k
c.    1 / K= 1 / k+ 1 / Hk
d.    1 / K= H / k+ 1 / k

40. At a particular temperature the equilibrium relation for distribution of a solute between a gas and a liquid phase is given by y =2x (x and y are in mole-fractions). If the individual gas and liquid phase mass transfer resistances are equally important for absorption of the solute in the liquid phase, the overall gas phase mass transfer coefficient, Ky’ is 
a.    equal to the individual gas phase mass transfer coefficient, K
b.    equal to individual gas phase mass transfer coefficeint k
c.    50 % of k
d.    33.3 % of k

41.A stage is a device 
a. in which mass transfer between two immiscible phases occurs 
b. in which two immiscible phases are brought into intimate contact
c. at the exit of which both phases are in equilibrium
d. where all (a), (b), (c) occur. 
43. Multistage contacting is preferred over single stage contacting in CPI because 
a. solvent requirement is less in multistage contacting
b. multistage contactor provides more than one stage in a contactor
c. equipment size is smaller in multistage contacting
d. (a)and (c) 


44. Kremser equation may be used to determine the number of stages in a staged column when 
a. the operating and equilibrium lines are straight 
b. the operating line is straight, but the equilibrium relation is curved c. the operating line is curved, but the equilibrium line is straight
d. both the operating and equilibrium lines are curved 


45. A good solvent for gas absorption should have 
a. high vapor pressure and low viscosity
b. high vapor pressure and high viscosity
c. low vapor pressure and low viscosity
d. low vapor pressure and high viscosity 


46. The solvent widely employed for natural gas dehydration is 
a. monoethanolamine
b. ethylene glycol
c. conc. sulfuric acid
d. calcium chloride 


47. For sweetening of sour gases, solvents that are widely employed are 
a. mono-and diethanolamines
b. wash oil of molecular weight higher than 300
c. aqueous NaOH solution
d. both (a) and (c) 


48. The correct operating line corresponding to minimum solvent flow rate in a countercurrent absorber 
a. OA
b. OB
c. OC
d. none of these 


49. For a given gas and liquid flow rates and a specified gas phase concentration change, the number of plates in a plate column is N. If the gas and liquid flow rates are doubled, the number of plates required for the same gas-phase concentration change will be 
a. N/2
b. 2N
c. N
d. between N and 2N 


50.Mole fraction, y, is related to the mole ratio, Y, by the relation 
a.    y = Y / 1 – Y 
b.    y = Y / 1 + Y 
c.    y = 1 – Y / 1 + Y
d.    y = 1 - y /Y (1+Y) 

51. Absorption factor is defined as 
a. mGL                 b. mG/L      c. G/mL                d. L/mG 

52. The number of plates in a plate column will be larger for L / mG 
a. greater than one          b. less than one               c. none of these 

53. The expression for HtOG is 
a. (yBM*G/KGa Pt)                   b. (yBM* Pt/KGaG)
c. (G /K
GaPtyBM*)                   d. (yBM* /KGa PtG) 

54. Height of transfer unit gives an idea about 
a. the ease of separation                                           b. the degree of separation 
c. the difficulty in achieving the separation             d. both (b) and (c) 

55. Height of transfer unit (HtOG) and height equivalent to a theoretical plate (HETP) are equal when L/mG is 
a. greater than one
b. less than one
c. equal to one
d. between 0.5 and 1 


56. HtOG is equal to HtG when
a. the gas phase resistance is negligible
b. the liquid phase resistance is negligible
c. both gas and liquid phase resistances are equally important
d. none of the above is correct 


57. For a certain gas absorption process (dilute gas), HtG = 0.3 m, HtL = 0.24 m and L/mG = 1.2. Then HtOG is equal to 
a. 0.588 m
b. 0.5 m
c. 0.6 m
d. 0.49 m 


58. Which of the following relation is correct?(assume that the gas is dilute) 
a. HtoG = HtG + (L/mG) HtL 
b. HtoL = HtG + (mG/L) HtL 
c. HtoG = HtL + (L/mG) HtG 
d. HtoL = HtL + (L/mG) HtG

59. Number of transfer unit gives us an idea about 
a. the degree of separation
b. the difficulty of separation
c. the ease of separation
d. none of these 


60. The correct expression for NtOG is 

61. For absorption of a dilute gas in a liquid, where the gas undergoes an irreversible chemical reaction, the correct expression for NtoG is 
a.    ln (y+ y2
b.    ln (y– y2
c.    ln [(y- y2) /( y+ y2)] #9; 
c.    ln (y/ y2
Where yand yare, respectively, the mole-fractions of the solute gas at the inlet and the outlet. 

62. Which of the following statements is / are correct? 
a. NtoG depends on the equilibrium characteristics of a system
b. N
toG can be manipulated by manipulating gas and liquid flow rates c. NtoG depends on packing characteristics
d. N
toG depends on gas flow rate 

63. For absorption of a highly soluble gas in a liquid, fraction of the gas absorbed in one transfer unit is 
a. 0.368       b. 0.534       c. 0.638       d. 0.771 

64. Number of gas phase transfer unit is given as 
a. (overall change in gas phase concentration)/(average driving force)
b. (average driving force)/(overall change in gas phase concentration)
c. (overall change in gas phase concentration)(average driving force)
d. (overall change in gas phase concentration) – (average driving force)
65. Absorption accompanied by heat evolution results in 
a.    increased solubility of gas in the liquid 
b.    larger number of plates (than that required for isothermal absorption) for the same degree of separation 
c.    increased capacity of the absorber 
d.    none of the above 

66.Lewis number, Le is given by 
a. Sc /Pr               b. Re.Pr       c. Sc.Pr       d. Sh.Pr 

67. Adiabatic saturation temperature is attained by the 
a. gas
b. liquid
c. both gas and liquid 


68. Dry bulb temperature of a gas is 
a. less than the wet bulb temperature
b. more than the wet bulb temperature
c. equal to the wet bulb temperature
d. none of the above 


69. Relative humidity is the ratio of 
a.    actual humidity to the saturation humidity at the gas temperature 
b.    partial pressure of the vapor to the vapor pressure of the liquid at the gas temperature 
c.    mass of vapor to the mass of vapor free gas 
d.    none of these 

70. At all humidities other than 0 and 100 per cent, the percentage humidity is 
a. more than the relative humidity
b. equal to the relative humidity
c. less than the relative humidity
d. none of the above 


71. Heat in BTU necessary to increase the temperature of 1 lb of gas and its accompanying vapor by 10F is called 
a.    latent heat 
b.    specific heat 
c.    sensible heat 
d.    humid heat 

72. The dew point of a saturated gas is equal to the 
a. gas temperature
b. adiabatic saturation temperature
c. wet bulb temperature
d. none of these 


73. In a cooling tower water is cooled from 95 0F to 80 0F by exposure to air with a wet-bulb temperature of 70 0F. Then the "approach" is 
a. 250
b. 200
c. 150
d. 100

74. For question no. 73, the "range" is 
a. 250F        b. 200F        c. 150F        d. 100

75. Heat required to vaporize 1 lb of water is roughly 
a. 1 BTU 
b. 10 BTU
c. 100 BTU
d. 1000 BTU 


76. The lowest temperature to which water can be cooled in a cooling tower through out the year depends on 
a. the summer dry bulb temperature
b. the dew point
c. the maximum wet bulb temperature
d. none of these
77. Adiabatic saturation line and wet bulb temperature line are the same for the system 
a. air – water                   b. nitrogen – benzene
c. nitrogen – toluene       d. air – benzene


78. If a warm vapor-gas mixture is contacted with cold liquid so that the humidity of the gas is 
a. greater than that at the gas-liquid interface,
b. vapor will diffuse toward the liquid and gas will be dehumidified
c. mass transfer will occur from the liquid to the gas and the gas will be humidified
d. sensible heat transfer will occur from the gas to the liquid
79. Purge of a small amount of water from a cooling tower is necessary in order to keep the load on the cooling tower at a specified level 
a. keep the dissolved salt concentration at a specified level 
b. both (a) and (b)
c. neither (a) nor (b) 


80. Dew point of a gas-vapor mixture (for a fixed vapor mole – fraction in gas) 
a. increases with an increase in gas dry – bulb temperature
b. decreases with an increase in gas dry – bulb temperature
c. increases with an increases in pressure
d. increases with a decrease in pressure 


81. During evaporative cooling process with recirculated water, which one of the following will remain constant? 
a. partial pressure of vapor
b. relative humidity
c. dry bulb temperature
d. wet bulb temperature 


82. During evaporative cooling process with recirculated water, which one of the following increases? 
a. partial pressure of vapor
b. relative humidity
c. wet bulb temperature
d. both (a) and (b)
83. When a gas-vapor mixture is cooled by sensible heat transfer 
a. relative humidity increases
b. relative humidity decreases
c. wet bulb temperature decreases
d. both (a) and (c) 


84. If Pis the partial pressure of vapor A in a vapor – gas mixture and Pis the saturation vapor pressure of liquid A, condensation of vapor-gas mixture just begins when 
a. P> PS                 b. P < PS               c. P = P

85. During adiabatic saturation of unsaturated air the parameter that remains substantially constant is 
a. dry bulb temperature
b. wet bulb temperature
c. dew point
d. humid volume 


86. We have an unsaturated air-water vapor mixture at a dry bulb temperature of the 40oC.The dew point for the mixture is 20 0C. The mixture is passed through a water spray chamber maintained at 17oC. The air, on passage through the chamber, will be 
a. cooled at the same relative humidity
b. cooled and humidified
c. cooled and dehumidified with an increase in wet bulb temperature
d. cooled and dehumidified with an decrease in wet bulb temperature 


87. Distillation is particularly important in 
a. petroleum refining
b. manufacture of sulfuric acid
c. vegetable oil hydrogenation
d. all (a), (b) and (c) 


89. Separation of components by distillation is not possible for 
a. > 1                 b. < 1                 c. = 1 

90. The relative volatility 
a. is independent of pressure
b. decreases with increasing pressure
c. increases with increasing pressure 

d. increases with increasing pressure and temperature 

91. An example of an ideal solution is 
a. a mixture of benzene, toluene and xy lene
b. a mixture of water and ethanol
c. a mixture of acetone, ethanol and n-butanol
d. none of these 


92. In distillation separation is accomplished by application of 
a. heat
b. solvent
c. adsorbent
d. none of these 


93. Raoults law is applicable to 
a. ideal solutions
b. real solutions
c. all solutions
d. non-ideal gases 


94. For ideal solutions relative volatility, , is related to the vapor pressure of components in a binary mixture according to the relations : 
a.    = PPB
b.    = P/PB
c.    c. = P/PA
d.    = 1 /PAP

95. Minimum boiling azeotrope occurs when the total pressure curve at a constant temperature passes through 
a. a maximum
b. a minimum
c. a maximum followed by a minimum
d. a minimum followed by a maximum
96. One of the examples of minimum boiling azeotropes is a mixture of 
a. benzene and toluene
b. hydrochloric acid and water
c. ethanol and water
d. none of these 


97. Steam distillation is usually employed for 
a. insoluble liquids
b. a component which is heat sensitive
c. miscible liquids
d. both (a) and (b) 


98. A system comprising of two insoluble liquids, A and B, will boil when the total pressure Pt is equal to 
a. PAsat + PBsat
b. xApAsat + xBpBsat 
c. xA g ApAsat + xB g BpBsat
d. none of these 

99. In azeotropic mixture, the equilibrium vapor composition at the azeotropic point 
a.    is less than the liquid composition 
b.    is equal to the liquid composition 
c.    is more than the liquid composition 
d.    may be more or less than the liquid composition, depending upon the nature of the system 

100. Positive deviation from Raoult’s law is exhibited by a mixture whose total pressure is 
a. greater than that computed for ideality
b. less than that computed for ideality
c. greater than the sum of the vapor pressures of the components
d. none of the above 


101. One of the examples of maximum boiling azeotropes is a mixture of 
a. hydrochloric acid and water
b. acetone and chloroform
c. benzene and cumene
d. both (a) and (b) 


102. In batch distillation with constant reflux, the overhead product purity 
a. decreases with time
b. increases with time
c. does not vary with time
d. none of the above 


103. For a multicomponent system the bubble point means that temperature when 
104. For a multicomponent system the dew point is that temperature when 
105. In flash vaporization, the product vapor 
a.    is always in equilibrium with the liquid leaving the flash chamber 
b.    is never in equilibrium with the liquid leaving the flash chamber 
c.    may be in equilibrium with the liquid leaving the flash chamber and the extent of equilibriation depends on the vapor – liquid contact time in the chamber 
d.    is 100% pure. 

106. In order to obtain an overhead product of constant composition from a batch distillation column, the reflux ratio should be 
a. held at a large and constant value
b. increased gradually
c. decreased gradually
d. minimum 


107. In a continuous distillation column as the reflux ratio is increased, the overhead product purity 
a. increases
b. decreases
c. may increase or decrease, dependingon the system
d. remains constant 


108. At total reflux in continuous distillation the number of plates is 
a. minimum
b. maximum
c. infinite
d. none of the above 


109. At total reflux 
a.    the enriching section operating line merges with the diagonal, but the exhausting section operating line does not 
b.     the exhausting section operating line merges with the diagonal, but the 
c.     c. both the enriching and the exhausting section operating lines merge with the diagonal 
d.     d. the enriching section operating line reduces to a point 

110. Fenske’s equation is used to calculate number of plates in a distillation column 
a. at total reflux
b. for system having constant relative volatility
c. at minimum reflux
d. for both (a) and (b) 


111. Minimum reflux ration corresponds to that situation 
a.    when infinite number of theoretical stages are required for the separation desired 
b.    when minimum reboiler heat load is required 
c.    when minimum condenser cooling load is required 
d.    when all (a), (b), (c) are true 

112. The driving force for separation by distillation is the highest 
a.    at total reflux 
b.    at minimum reflux 
c.    at an intermediate reflux between the total and the minimum 
d.    at the point of intersection of the enriching section operating line with the equilibrium curve 

113. At total reflux the reflux ratio is 
a. zero                  b. one 
c. infinite              d. neither zero nor one, but finite 

114. At the reflux ratio increases the slope of the enriching section operating line 
a. decreases
b. increases
c. remains constant
d. may increase or decrease, depending on the relative volatility of the system. 


115. If xis the mole fraction of the more volatile component in the overhead product and R is the reflux ratio, the intercept and slope of the enriching section operating line in a McCabe –Thiele diagram is 
a. xD/(R+1) and (R+1)/R
b. R/(R+1) and x
D/(R+1)
c. x
D/(R+1) and R/(R+1)
d. R/(x
D+1) and xD/(xD+1) 

116. When the feed to a distillation column is a saturated liquid, the slope of the feed line is 
a. zero
b. one
c. infinity 

d. 0.5 

117. 100 moles of vapor per hour is leaving the top plate of a continuous distillation column and overhead product at the rate of 50 moles/hr is being withdrawn. Then the reflux ration is 
a. 0.5                    b. 1.0 c.                2.0              d. 3.0 

118. The distillate flow rate from a distillation column is 100 kmol / hr and the reflux ratio is 2. The flow rate of vapor from the top plate in kmol /h is 
a. 100          b. 200         c. 300          d. 50 

119. In the enriching section of a continuous distillation column 
a. vapor is enriched with respect to the more volatile component
b. liquid is enriched with respect to the more volatile component
c. both vapor and liquid are enriched with respect to the more volatile component
d. transfer of the more volatile component occurs from the vapor to the liquid
120. A partial condenser is considered as a theoretical plate when 
a.    vapor and liquid leaving the condenser are in equilibrium 
b.    in reality it is provided with a plate 
c.    the condensate is removed as rapidly as it forms 
d.    the statement is wrong; a partial condenser can never be considered as a theoretical plate
121. When open is employed for heating in continuous distillation column, the stripping section operating line in McCabe-Thiele diagram passes through 
a.    [xw’ w
b.    [o, x w
c.    [x w’ o] 
d.    [o, o] 
xis the mol fraction of the more volatile component in bottom product 

122. When saturated vapor is fed to a distillation column, the slope of the feed line is 
a. zero
b. one
c. between zero and one
d. infinity 


123. The ratio of "slope of the enriching section operating line corresponding to minimum reflux" to "slope of the operating line corresponding to reflux large than minimum" is 
a. less than one
b. greater than one
c. equal to one
d. equal to zero
124. When feed to a distillation column is a mixture of 50% vapor and 50% liquid, the slope of the feed line is 
a. zero                  b. one 
c. minus one         d. 0.5 

125. Ponchon-Savarit method of calculation of number of theoretical plates of a distillation column is based on 
a. material balance only
b. enthalpy balance only
c. both material and enthalpy balances
d. assumptin of consist molal overflow
126. If Ris the minimum reflux ratio the optimum reflux ratio is 
a.1.25 to 1.5 Rm                              b.2 Rmc.2.5 to 3.5 Rm                                d.5 R

127. Which one of the following is the Rayleigh equation? 
 [F : moles of feed charged; x: mole fraction of the more volatile component in the feed; W : moles of residual liquid ; x: mole fraction of the more volatile component in the residual liquid] 

128. Rayleigh equation applies to 
a. differential distillation
b. flash vaporization
c. molecular distillation
d. multicomponent distillation 


129. If feed to a distillation column is introduced onto a plate one plate below the feed plate, the total number of theoretical plates required for a desired separation will 
a. decrease
b. increase
c. remain constant
d. may increase or decrease, depending on the state of feed. 


130. There is a relationship between the reflux ratio used in a distillation column and the column diameter. As the reflux ratio increases, the column diameter 
a. increases
b. decreases
c. remains unaltered
d. may increase or decrease, depending on the system. 


131. Azeotropic distillation is a special case of 
a. molecular distillation
b. differential distillation
c. flash vaporization
d. multicomponent distillation 


132. For azeotropic separation of acetic acid-water mixture the entrainer that is employed is 
a. isopropyl ether
b. isooctane
c. phenol
d. n-butyl acetate 


133. For azeotropic separation of ethanol-water mixture, the entrainer that is used is 
a. benzene
b. toluene
c. n-octane
d. none of these 


134. Distillation at reduced pressure is practised for separation of 
a. heat sensitive materials only
b. components having low volatilities at normal pressures
c. both and b
d. none of the above 


135. The minimum number of plates required for a desired separation by distillation 
a. depends on the thermal condition of the feed
b. does not depend on the thermal condition of the feed
c. depends on the mole fraction of the more volatile component in the feed
d. depends on the mole fraction of the less volatile component in the feed 


136. A solvent employed in a liquid-liquid extraction operation should preferably have 
a. low viscosity and low interfacial tension
b. high viscosity and low interfacial tension
c. low viscosity and high interfacial tension
d. high viscosity and high interfacial tension 


137. No separation by solvent extraction is not possible if the selectivity is 
a. 1
b. 10
c. 100 d. 1000 


138. Solvent extraction should preferably be carried out at temperatures
a. below the critical solution temperature
b. above the critical solution temperature
c. equal to the critical solution temperature 


139. On a distribution curve plait point is that point where 
a. y > x        b. y > x        c. y = x        d. y = 2x

140. At the plait point selectivity is 
a. zero
b. 1
c. 10
d. infinity 


141. There is a direct relationship between the distribution coefficient and the solvent requirement. As the distribution coefficient increases, the solvent requirement for a given separation 
a. decreases
b. increases
c. remains unaffected
d. may increase or decrease, depending on the system. 


142. The apex of an equilateral triangular coordinate (in ternary liquid system) represents 
a. a binary mixture          b. a ternary mixture         
c. a pure component        d. none of these 

143. In equilateral triangular coordinate a point on any side of the triangle represents 
a. a pure component        b. a binary mixture
c. a ternary mixture         d. none of the above 


144. As the interfacial tension of a liquid-liquid system decreases, the ease of Coalescence 
a. increases
b. decreases
c. remains unaltered 


145. For liquids of very small density difference, the most suitable extractor is 
a. a mixer-settler unit
b. a rotating disc contactor
c. a packed column extractor d. a centrifugal extractor 


146. Podielniak extractor is a special type of 
a. RDC
b. packed column extractor
c. centrifugal extractor
d. spray column extractor 


147. Which of the rollowing is / are correct? A spray tower is 
a. a multistage extractor
b. a single – stage extractor
c. a differential contact extractor
d. None of these 


148. Pulsing of a packed column extractor results in 
a. larger liquid-liquid interfacial area
b. higher mass transfer coefficient
c. both a and b
d. none of the above 


149. For extraction of penicillin from nutrient broth, the most suitable extractor is 
a. a rotating disc contactor
b. a packed column extractor
c. a mixer – settler unit
d. a centrifugal extractor 


150. Refer to the adjoining figure. According to the mixture rule 
a.     R/E = (x+xR)/x
b.     R/E = (x+ x)/(x+ xR
c.     R/E = (x – xM)/(x– xR
d.     R/E = x/ xR

151. For liquid-liquid systems that form emulsions, the most suitable contactor is 
a. a mixer – settler
b. an RDC
c. a centrifugal extractor
d. a pulsed packed column
152. The udex process is 
a.    a solvent extraction process in which benzene, toluene and xy lene present in catalytic reformates are extracted with sulfur dioxide or diethy leneglycol 
b.    an extractive distillation process employing phenol
c.    an azeotropic distillation process employing n-butyl acetate 
d.    an absorptive separation process for obtaining high purity p – xy lene from a mixture of m – and p – xy lene 

153.One of the solvent in the Duo-Sol process is 
a. methyl isobutyl ketone
b. isopropyl ether
c. propane
d. aqueous sodium hydroxide solution 


154.Mercaptans present in light distillates are removed by extraction with 
a. concentrated sulfuric acid solution
b. concentrated phosphoric acid solution
c. aqueous caustic soda solution
d. none of these 


155. In the hydrochloric acid route for the production of phosphoric acid, phosphoric acid is extracted from a mixture of aqueous phosphoric acid and calcium chloride solution by 
a. xy lene
b. phenol
c. C
– alcohols 
d. aniline 

156. In the Edeleanu process (one of the solvent extraction processes applied to light distillates in petroleum refineries) sulfur dioxide is used as a solvent. At the boiling point of sulfur dioxide, which is 14oF, the components which are miscible with sulfur dioxide are 
a. paraffin and naphthene hydrocarbons b. paraffin and aromatic hydrocarbons
c. naphthene and aromatic hydrocarbons d. aromatic and unsaturated hydrocarbons


157. RDC is widely used for liquid-liquid extraction operations in petroleum refineries 
a. because of superior contacting
b. because of larger capacities
c. because very quick change-overs of feedstocks are possible in RDC
d. all (a), (b), (c) 


158. The operation which is employed for the removal of caffeine from coffee is 
a. adsorption
b. crystallization
c. solvent extraction
d. fractional distillation 


159. Extraction by supercritical COis particularly important in 
a. food industry
b. petroleum refining
c. fertilizer manufacture
d. synthetic fibre production
160. The major application of the sulfolane extraction process is for 
161. In which adsorption may occur 
a. the production of benzene, toluene and xy lenes of high purity from a mixture of aromatics and nonaromatics 
b. the production of paraffins from a mixture of aromatics and nonaromatics 
c. the production of olefins from a mixture of aromatics and nonaromatics 
d. all (a), (b) and (c) 

of the following cases of heterogeneous phase contacting, the phenomena of 
a. gas-solid or solid-liquid contacting
b. gas-liquid or liquid-liquid contacting
c. both a and b 

d. none of the above 

162. Adsorption of a gas onto a solid 
a. is an exothermic process
b. is an endothermic process
c. does not product any heat effect
d. may be exothermic or endothermic, depending on the system 


163. Adsorption of a gas onto a solid can be conducted most efficiently at 
a. high pressure and low temperature
b. low pressure and low temperature
c. low pressure and high temperature
d. high pressure and high temperature 


164. For bulk separations adsorption becomes competitive with distillation when the relative volatility is 
a. less than about 1.25
b. between 1.5 and 2.0
c. more than 2.0
d. between 2 and 2.5 


165. A good adsorbent should have a 
a. high selectivity for the solute
b. sufficiently high capacity
c. long life 

d. all (a), (b), (c) 

166. The separation factor in adsorption varies with 
a. temperature only
b. adsorbent only
c. temperature and
d. adsorbent and often also with composition 


167. For an ideal Langmuir system the separation factor is 
a. independent of temperature
b. independent of adsorbent
c. independent of composition
d. none of these 


168. In adsorptive separation processes, what type of adsorption should occur? 
a. physical adsorption
b. chemisorption 


169. Physical adsorption is 
a. nonspecific and significant at relatively low temperatures
b. specific and significant at high temperature
c. specific and significant at low temperature
d. nonspecific and significant at high temperature 


170. In certain adsorptive separation processes differences in diffusion rates between molecules of comparable molecular weight are exploited to achieve useful separation between molecules. This type of separation is known as 
a. equilibrium separation
b. kinetic separation
c. chromatographic separation
d. none of these 


171. Kinetic separation is generally accomplished with 
a. zeolites and carbon sieves
b. silica gel
c. activated carbon
d. activated alumina 


172. A toxic solute present in an industrial wastewater is to be removed by its adsorption onto adsorbents in a single-stage operation. The equilibrium relation is given by Freundlich equation : 
Y* = mXwhere Y* = mass solute / mass solvent and X = mass solute/ mass adsorbent. Now keeping m constant, as n is varied from n > 1 to n < 1, the adsorbent requirement for the same degree of separation will 
a. increase
b. decrease
c. remain constant
173. For crosscurrent two-stage treatment of liquid solutions by contact filtration, when the adsorption isotherm is linear, the least total adsorbent results if 
a. the amounts used in each stage are equal
b. the amount used in stage 1 is twice that used in stage 2 

c. the amount used in stage 2 is twice that used in stage 1
d. the amount used in stage 1 is 10 times that used in stage 2 


174. The forces involved in physical adsorption are van-der-waals forces
a. electrostatic interactions
b. chemical interactions
c. both (a) and (b) 


175. The hypersorption process is a 
a. cocurrent adsorption process
b. countercurrent adsorption process
c. crosscurrent adsorption process
d. fixed bed adsorption process 


176. Regeneration of adsorbent by purge gas stripping is possible when 
a. the adsorbed species are strongly held
b. the adsorbed species are weakly held
c. the adsorbent contains several strongly-held adsorbates
d. the desorbate is of great value and needs to be recovered 


177. Regeneration of adsorbents containing several adsorbates of widely different adsorption affinities adsorbed on them is preferably done by 
a. pressure swing
b. thermal swing
c. purge gas stripping 

d. displacement desorption

178. The moisture content of a solid on dry basis is X. The moisture content on wet basis is 
a.    (1 + X)/ X 
b.    1 / (1 + X) 
c.    X / (1 + X) 
d.    (1 – X) /(1 + X) 

179. The moisture contained by a substance that exerts an equilibrium vapor pressure equal to that of pure liquid at the same temperature is known as
a. free moisture
b. equilibrium moisture
c. bound moisture
d. unbound moisture 


180. In drying operation moisture that is evaporated is 
a. equilibrium moisture
b. free moisture
c. bound moisture
d. unbound moisture
181. A solid can be dried completely by passing over it 
a. hot and humid air
b. completely dry air
c. saturated steam 

d. none of these 

182. In the constant-rate-period moisture that is evaporated is 
a. free moisture
b. equilibrium moisture
c. bound moisture
d. unbound moisture
183. When the average moisture content of a solid is equal to the critical moisture content, the drying rate is 
a. equal to the rate at constant – rate – period
b. less than the rate at constant – rate – period
c. more than the rate at constant – rate – period
d. none of these 


184. If drying occurs by convective heat and mass transfer (conduction and radiation effects are absent), the temperature at the solid surface is equal to 
a. the gas temperature
b. the wet-bulb temperature of the gas
c. the arithmatic mean of (a) and (b)
d. the dew point of the gas 


185. In a certain drying operation dry bulb temperature of air is 600C and the surface temperature 
of the solid is 300C. Assume that conduction and radiation effects are negligible. Now under 
otherwise uniform conditions if the dry bulb temperature of air is increased to 900C , the drying rate during the constant rate period will 
a. increase by a factor of 1.5
b. will remain substantially constant
c. will decrease by a factor of 1.5
d. will increase by a factor of 2 


186. The drying rate during the constant rate period for the use of cross circulation drying of a solid depends on 
a. the velocity of the drying gas
b. the gas temperature
c. the humidity of the drying gas
d. all (a), (b) and (c) 


187. In a certain process a solid will be dried from all surfaces. Under this condition the rate of drying during the constant – rate – period will 
a. increases proportionally with the thickness of the solid
b. decrease with increasing thickness
c. be independent of thickness
d. be none of these 


188. For the cases in question no. 187, the drying time between fixed moisture contents in the constant – rate – period will 
a. be independent of the thickness of the solid
b. be directly proportional to the thickness
c. will be directly proportional to the square of the thickness
d. will be inversely proportional to the thickness. 


189. If the drying rate, N, is plotted in the ordinate and the free moisture, X, is plotted in the abscissa, then the N vs. X curve will definitely pass through 
a. (0, NC
b. (Xe’ NC
c. (0, 0) 
d. none of these
[N
: drying rate at constant – rate – period; X: equilibrium moisture content] 

190. Assume that the rate-of-drying curve in the entire falling-rate-period is linear. Then the drying time between fixed moisture contents in the falling-rate-period is 
a. directly proportional to the solid thickness
b. inversely proportional to the solid thickness
c. independent of the solid thickness
d. directly proportional to the square root of the solid thickness 


191. When drying occurs due to the movement of moisture through a solid, the drying time between fixed moisture contents is 
a. directly proportional to the thickness of the solid
b. inversely proportional to the square of the thickness
c. directly proportional to the square of the thickness
d. inversely proportional to the thickness 


192. Drier that is most suitable for drying of milk is 
a. rotary drier 
b. drum drier
c. freeze drier
d. spray drier 


193. Rotary driers are employed for drying solids which are 
a. free-flowing and granular
b. sticky
c. gummy
d. none of these 


194. The critical moisture content is a function of 
a. material properties
b. rate of drying during the constant-rate-period
c. particle size
d. all (a), (b), (c) 


195. A continuous rotary drier is filled with material to 
a. 1 to 2% of the shell volume
b. 10 to 15% of the shell volume
c. 70 to 75% of the shell volume
d. 95 to 97% of the shell volume 


196. In countercurrent rotary driers the exit gas temperature is usually
a. higher than the product temperature 
b. lower than the product temperature
c. equal to the product temperature
197. For drying a heat – sensitive material in a rotary drier, the gas flow should be 
a. cocurrent
b. countercurrent
c. cocurrent or countercurrent 


198. Rotary driers are usually operated with a negative internal pressures to 
a. achieve uniform drying at all locations in the drier
b. prevent dust and vapor escape through the rotating seals
c. minimize dry air requirement
d. avoid any damage of the material of construction of the drier internals 


199. Drying of detergent solution to produce detergent powder is accomplished in a 
a. tunnel drier
b. spouted bed drier
c. spray drier
d. freeze drier 


200. Rotary driers are usually rotated at peripheral speeds of 
a.    0.2 to 0.5 m / s 
b.    0.01to 0.05 m / s 
c.    4 to 5 m / s 
d.    d. 10 to 15 m / s 

201. The length to diameter ratio of most rotary driers is around 
a.    1 to 1.5 
b.    4 to 10 
c.    50 to 100 
d.    none of these 

202. Consider diffusion of A through stagnant B. At 1 atm and 298 K, N= 2.3x10--5 kmol / ms.
If the pressure is increased to 10 atm (all other parameters including the driving force for mass transfer remain unchanged), Nwill be 
a. 2.3x10-6 kmol / m2s
b. 2.3x10
-4 kmol / m2s
c. 2.3x10
-5 kmol / m2 .s
d. 1.7x10
-5 kmol / m2s
203. In a laboratory experiment on mass transfer, CObubbles are rising vertically upwards 
through a pool of a liquid taken in a narrow long tube. Which of the following models will be most appropriate in describing the mass transfer process? 
a. film model
b. penetration model
c. surface renewal model
d. any of the foregoing 


204. Consider a case where mass transfer of a solute gas A takes place through stagnant B and the mass transfer coefficient based on mole-fraction driving force is ky. How is the coefficient related to ky’, the mass transfer coefficient applicable for equimolar counterdiffusion? 
a.    kyPBM = ky'
b.    kPBM / RT = ky'
c.    kyyBM = k
d.    kyBM = ky'

205. Consider a gas absorption process ; for this case L/mG = 1. This means driving force for mass transfer at the top of the column is 
a. greater than that at the bottom of the column
b. smaller than that at the bottom of the column
c. equal to that at the bottom of the column
206. Typical superficial gas velocity at the bottom in a countercurrent packed absorber is around 
a.    1 cm / s 
b.    1 m / s 
c.    50 m / s 
d.    200 m / s 

207. A careful examination of the solvent properties may give us a clue to the controlling resistance in a gas absorption process. Consider natural gas dehydration in a plate column using triethylene glycol in order to reduce the water content of the gas so as to prevent formation of solid hydrates. The liquid flow rate is much lower as compared to the gas flow rate. The plate column is fitted with bubble-cap trays and the liquid viscosity is high. Which resistance is likely to control the dehydration? 
a. gas – side 
b. 
liquid – side 
c. 
cannot answer
d. inadequate information
208. Many industries generate liquid streams containing 0.01 to 2 wt % NHnitrogen which have 
an adverse effect when discharged into the evironment. Therefore, NHshould be removed from 
aqueous waste streams by, say, stripping. Now for stripping, what kind of solution pH should be maintained? 
a. 1 to 2
b. 4 to 5
c. 7
d. 11 to 12 


209. Liquid flow rate has a significant effect on overall (KGa) value in gas absorption in a packed 
tower. Under otherwise uniform conditions, a doubling of the liquid irrigation rate typically will increase the overall (KGa) value by 
a. 5 %         b. 23 %       c. 59 %        d. 84 % 

210. Consider gas absorption in a packed column. The operation is gas-film controlled. For a fixed packing height, if the gas flow rate is increased, the solute removal efficiency will 
a. greatly decrease
b. increase substantially
c. decrease slightly 


211. Total liquid hold-up in a packed column is the sum of static hold-up and operating liquid hold- up. On which of the following factors does static hold-up depend? 
a. surface area of the packing
b. surface roughness of the packing
c. contact angle between the packing surface and the liquid
d. none of the foregoing 


212. With increasing liquid viscosity, liquid hold-up in a packed column
a. increases
b. decreases
c. remains unchanged 


213. Consider a packed column performing gas-liquid contacting. At a constant liquid hold-up, if the liquid density is lowered (all other parameters remaining unchanged), what happens to the gas pressure drop? 
a. decreases
b. increases
c. remains unchanged
214. Consider a packed column in which gas and liquid flow downward in the same direction (cocurrent operation). At the same liquid rate, if the gas flow rate is increased, total liquid hold-up will 
a. increase
b. decrease
c. remain substantially constant 


215. Under otherwise uniform conditions, the capacity of a packed column of a given diameter will be 
a. higher for cocurrent operation
b. lower for cocurrent operation
c. independent of the mode of operation 


216. As compared to a liquid-film controlled operation, the value of (KGa) for a gas-film controlled operation will be 
a. much lower
b. much higher
c. almost the same 


217. In the layout plan for a vacuum distillation unit operating at 60 mm Hg supported by a barometric condenser the appropriate place for location of the vacuum drum for collecting the distillate will be 
a. at ground level
b. 2m above ground
c. 5m above ground
d. 10m above ground 


218 The presence of foam in a packed bed causes 
a. a marked decrease in pressure drop
b. a marked increase in pressure drop
c. practically no change in pressure drop 


219. Consider a packed column in which air-water contacting takes place at atmospheric pressure. If, under otherwise uniform conditions, water is replaced by an organic liquid for which the surface tension is much lower, what will happen to the operating hold-up? 
a. will increase
b. will decrease
c. will remain practically unchanged 


220. Consider a situation where COis being absorbed in a 4% aqueous NaOH solution in a packed tower. The process is liquid-phase mass transfer controlled. For such a process, the overall gas- phase mass transfer coefficient (KGa) will be 
a.     strongly dependent on gas flow rate 
b.     mainly dependent on liquid flow rate 
c.     dependent on both gas and liquid flow rates to almost the same extent

221. In a certain mass transfer experiment, pure acetone evaporates into air. The process is 
a.    gas-film controlled 
b.    liquid-film controlled 
c.    both gas- and liquid – film controlled 

222. The liquid hold-up below the loading region in a packed column is 
a. primarily a function of liquid flow rate
b. independent of liquid flow rate
c. a strong function of gas flow rate
d. a function of both gas and liquid flow rates 


223. Consider a theoretical plate in a plate column. Now state which one of the following is true? 
a. the gas entering the plate is in equilibrium with the liquid leaving the plate 
b. the gas leaving the plate is in equilibrium with the liquid entering the plate
c. the liquid entering the plate is in equilibrium with the liquid leaving the plate d. the gas leaving the plate is in equilibrium with the liquid leaving the plate 


224. Plastic pakings are extensively used in scrubbers. Which of the following points are applicable for plastic packings? 
a. they have light weight and cheap
b. some organic compounds may destroy them
c. they are resistant to mechanical damage and attack by acids and alkalis d. all of the above 


225. Under otherwise uniform conditions, the static liquid hold-up for structured packing will generally be 
a. greater than
b. less than
c. almost equal to that for random packing 


226. Absorbers are usually designed for a gas pressure drop 
a.    between 1 to 4 inch H2O per ft. of packed depth 
b.    between 10 to 40 inch H2O per ft. of packed depth 
c.    between 0.1 to 0.4 inch H2O per ft. of packed depth 
d.    any of (a), (b) or (c) because there is practically no restriction on this parmeter for rational design of a packed absorber 

227. For systems that tend to foam moderately, the design pressure drop at the point of greatest loading should be a maximum of 
a. 0.25 inch H2O / ft of packed depth
b. 1.5 inch H
2O / ft of packed depth
c. 10 inch H
2O / ft of packed depth
d. 25 inch H
2O / ft of packed depth 

228. Define distribution coefficient (m) for extraction as follows :m = solute concentration in extract / solute concentration in raffinate . For m > 1, major resistance to mass transfer will lie in 
a. extract phase      b. raffinate phase 

229. At the plait point, the distribution coefficient, m, is 
a. zero
b. one
c. greater than one d. less than one 


230. Consider a system : extraction of H2S present in LPG by aqueous ethanolamine solution. The major resistance to mass transfer in this system will be in 
a. organic phase              b. aqueous phase 

231.There are three classes of equipment used for extraction operation : mixer – settlers, packed and plate columns, and centrifugal contactors. Now which of the following points is / are applicable for mixer – settler ? 
a. they occupy large floor space 
b. they provide high stage efficiencies
c. they require large solvent inventories
d. all of the foregoing 


232. When the difference between the density of the light phase and the density of the heavy phase is 4% or lower, which of the following extraction equipment will you prefer? 
a. mixer - settlers
b. centrifugal extractors
c. packed column
d. plate column 


233. In the absorption of a solute gas from a mixture containing inerts in a solvent it has been found that the overall gas transfer coefficient is nearly equal to the individual gas film transfer coefficient. It may therefore, be concluded that 
a.    the process is liquid film controlled 
b.    the gas is sparingly soluble in the liquid 
c.    the mass transfer rate can be substantially increased by reducing the thickness of the liquid film 
d.    the mass transfer rate can be substantially increased by reducing the thickness of the gas film 

234. Lewis number =1 signifies 
a. Pr=Sc               b. Pr=Re               c. Sc=Re               d. Nu=Sh 

235. For Reynolds analogy to hold, Schmidt number is 
a. zero
b. one
c. hundred
d. thousand 


236. j-factor for mass transfer (jD) is given by 
a. jD= St. Re 1/3 b. jD=St. Sc 
c. jD=St.Sc 2/3 d. jD=Sh.Sc2/3 

237.Weber number is a ratio of 
a. inertial forces to gravity forces
b. inertial forces to shear forces
c. gravity forces to surface tension forces
d. inertial forces to surface tension forces 


238. In a bubble column, fractional gas hold – up is 0.15 and the interfacial area is 3 cm2 / cm3. What is the average bubble diameter in mm? 
a. 1 mm       b. 2 mm       c. 3 mm       d. 6 mm 

239. Consider a bubble column (liquid batch, gas continuously flowing) for which superficial gas velocity is 0.05 m/s and the fractional gas hold-up is 0.1. What is the step velocity? 
a.    0.005 m / s 
b.    0.5 m / s 
c.    0.032 m / s 
d.    0.87 m / s 

240. Which of the following is a reasonable assumption for a tall countercurrent bubble column (both gas and liquid are continuously flowing) ? 
a. gas well-mixed, liquid well-mixed
b. gas well-mixed, liquid plug-flow
c. gas plug-flow, liquid plug-flow
d. gas plug-flow, liquid well-mixed 


241. Consider a leaching operation; liquid flows through a bed of solid particles. The bulk density is 60 lb / ft3 and the particle density is 100 lb / ft . The fractional void volume in the bed is 
a. 0.2           b. 0.3          c. 0.4           d. 0.5

242. In leaching operation, for constant under low, y* / x is 
a. greater than one
b. equal to one
c. less than one 

d. equal to 0.5 

243. Which of the following is the "capillary number"? 
a. (K/g L) (g/gCb. (/Kg L) (g/gCc. (/Kg L) (gC/g) d. (KL/g) (g/gC
K : permeability; : liquid surface tension; rL: liquid density 

244. Large depths on trays (reasonable gas velocities) in a tray column lead to 
a. high pressure drop but high tray efficiencies
b. excessive entrainment
c. none of the foregoing
245. Recommended plate spacing for tower dia of 12 to 24 ft is 
a. 6 inch      b. 20 inch    c. 24 inch     d. 36 inch 

246. Weeping occurs when gas velocities (in a plate column) are 
a. too high 
b. too low 

247. In the event of severe weeping, no liquid reaches the downspouts. This phenomenon is known as 
a. priming
b. coning
c. dumping
d. none of the foregoing 


248. Which of the following is an exaggerated condition of liquid evtrainment? 
a. priming    b. coning     c. dumping            d. weeping 

249. Which of the following statements is true for a packed column (as compared to plate column)? 
a. requires larger pressure drop
b. side streams can be withdrawn easily
c. frequent cleaning can be done
d. provides substantially smaller liquid hold-up
250. Outlet weirs (provided on the plate in a plate column) maintain a desired liquid level on the plate. Inadequately large weir height may cause 
a. higher pressure drop (per tray)
b. down comer backup and significant entrainment c. weeping tendency
d. all of the foregoing 


251. Common weir height for absorbers and strippers is 
a.    1⁄2 inch to 1 inch 
b.    3 to 4 inch 
c.    9 to 10 inch 
d.    15 inch and above 

252. How many degrees of freedom does a binary liquid-liquid system have? 
a. zero         b. one          c. two          d. three 

253. How many degrees of freedom does a ternary liquid-liquid system have? 
a. zero         b. one          c. two          d. three 

254.In a countercurrent liquid-liquid extractor, slip velocity [Ud/+UC/(1-)] where Uand Uc are, respectively, dispersed and continuous phase superficial velocities and is the fractional dispersed phase hold-up) is Us. In a packed countercurrent extractor, slip velocity is Us . Now which of the following relations is correct? 
a.    Us'/Us<1 
b.    Us’ / U= 1 
c.    Us'/Us>1
d.    d. Us'/Us=μ

255. In a binary distillation column if the feed contains 40 mol% vapour, the q line will have a slope of 
a. 1.5           b. -0.6         c. -1.5         d. 0.6 

256. Knudsen diffusivity increases 
a.    with the square root of temperature and inversely with the square root of molecular weight 
b.    with temperature only (directly proportional) 
c.    with the square root of molecular weight 
d.    with molecular weight only (directly proportional) 

257. Knudsen diffusivity falls in the range of 
a.    1 – 2 cm/ s 
b.    10 –1 – 10 – 4 cm/ s 
c.    10 -10 – 10 –14 cm/ s 
d.    none of the foregoing

258. Write down the expressions for mass transfer for the following theories of mass transfer 
a.     i)  Film theory 
b.     ii)  Penetration theory 
c.     iii)  Surface renewal theory 
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259. What is the significance of film thickness in mass transfer ? 
(a) The actual thickness of the stagnant film that adheres to the phase boundary.
(b) The depth of penetration of solute in a fresh element of fluid (which has been brought to the interface from the bulk fluid by the fluid motion) during its stay at the interface.
(c) The thickness of a stagnant film of fluid that offers the same resistance to mass transfer as is actually being offered under the existing hydrodynamic conditions. 


260. How does the age of a liquid element affect the rate of mass transfer in it? 
(a) the rate of mass transfer increases with increase in age
(b) the rate of mass transfer decreases with increase in age
(c) the rate of mass transfer remains unchanged with age 


261. For absorption of a gas from a bubble rising steadily through a stagnant liquid, which one of the following theories of mass transfer do you think to be most appropriate? 
(a) Film theory
(b) Surface Renewal theory
(c) Penetration theory. 


262. Consider a thin sheet of naphthalene placed in a stream of air in turbulent flow. Then the “thickness of the film” on the sheet will be 
(a) Greater than the average thickness of the boundary layer
(b) Less than the average thickness of the boundary layer
(c) Equal to the average thickness of the boundary layer
263. Which of the following may be the unit of surface renewal rates ? 
(a) m/s                         (b) m2/s                       (c) s-1 

264. What will be the effect of the following changes on the average rate of surface renewal in a packed tower ? 
 (i) With increase in L (G = Constant), s will 
(a) increase (b) decrease (c) remain unchanged. 
(ii) With increase in G (L = constant), s will 
(a) increase (b) decrease (c) remain unchanged. 

265. Consider a bubble of pure gas A rising steadily through a stagnant bulk of liquid B. The following data are given : 
DAB = 3.14 x 10-5 cm2/s.; d (bubble dia) = 0.5 cm 
U (bubble rise velocity) = 20 cm/s.; CA* (solubility) = 0.2 mol/L 
(i) What is the life (in seconds) of individual liquid elements involved in mass transfer ? 
(a) 10 (b) 0.1 (c) 0.025 
(ii) What is the average rate of surface renewal (s-1) ? 
a) 40 b) 0.2 c) 20 
(iii) What is the value of average mass transfer coefficient in cm/sec ? 
a) 0.2 b) 0.04 c) 0.5 
266. Which one of the following is the probable value of the Schmidt Number for diffusion of 
(i) NHin air at 00C; 
a) 4.05 b) 0.665 c) 0.0513 
(ii) NHin water at 150C ? 
a) 5000 b) 1.261 c) 660 
267. What is the expression for Sherwood number for gas phase mass transfer. 

268. A solid coated on the surface of a flat plate dissolves in a liquid flowing past the plate at/angle of incidence. Diffusion of the solute occurs through the boundary layer formed on the plate. In such a case the thickness of the momentum boundary layer is expected to be greater than the concentration boundary layer if the Schmidt Number, Sc is 
(a) greater than 1 (b) less than one (c) equal to 1.

269. How do you define Stanton Number, St for mass transfer ? 
270. What is the expression for Colburn factor, j
271. The Sherwood Number, Sh, 
(a) independent of Reynolds number             (b) increases with Reynolds number           
(c) decreases with Reynolds number. 


272. The Colburn factor, jD,
(a) increases with Reynolds number; 
(b) decreases with Reynolds number 
(c) is independent of Reynolds number. 

273. When we express the mass transfer rate with the help of mass transfer coefficient; the driving force is 
(a) concentration gradient
(b) interfacial concentration of solute
(c) concentration difference. 


274. The effects of which of the following terms are included in the mass transfer coefficient, k?
(a) Solubility of the solute and the interfacial area of contact
(b) diffusivity of the solute and the hydrodynamics of the system
(c) vapor pressures of the solute and the medium 


275. Air is flowing over a pan of water at a velocity of 60 ft/sec. Which of the following may be roughly the value of the mass transfer coefficient, kin lb-mole / (hr(ft2)(atm) for the vaporization ? 
(a) 1.02 (b) 0.0345 (c) 562.5 

276. In a gas-liquid system, Henry’s law applies in the form, y* = mx. Then the ratio of the mass transfer resistances in the liquid and gas phases will be : 
277. For absorption of SOin water, 
(a) the gas phase resistance becomes controlling 

(b) the liquid phase resistance becomes controlling
(c) both gas and liquid phases are expected to offer comparable resistance. 
278. Absorption of ammonia in water and that of hydrogen chloride in water are 
(a) both gas phase resistance controlling
(b) both liquid phase resistance controlling
(c) neither of (a) and (b). 
279. Regarding the values of mass transfer coefficients for absorption of polynuclear hydrocarbons (like naphthalene, anthracene etc.) from coke oven gas in light absorption oil it is expected that 
(a) k>> k(b) k<< k(c) No conclusion 
280. Overall liquid phase mass transfer coefficient, kL, has the same unit as 
(a) momentum (b) velocity (c) acceleration 
281. The individual gas phase mass transfer coefficient, ky, has the same unit as 
(a) diffusivity (b) molal concentration gradient (c) molal flux. 
282. Molten pure naphthalene is being vaporised by passing air through it in a plant manufacturing phthalic anhydride. The controlling mass transfer resistance will occur in 
(a) the gas phase (b) the molten mass (c) in both the phases. 
283. For absorption of 8% COby 10% monoethanol amine solution, the controlling mass transfer resistance is expected to occur in 
(a) gas phase (b) the liquid phase (c) in both the phases. 
284. Gas A is being absorbed by liquid B in 1 atm. total pressure. The following data are available : 
Mole fraction of A in bulk gas, y= 0.2 
Partial pressure of A at the gas-liquid interface, pAi = 0.1 atm. 
Concentration of A in bulk liquid, C= 0.01 mol/L 
Henry’s law applies in the form, P = HC, H = 5 (atm) (L)/(mol) 
In such a case, how do the values of overall gas-phase coefficient- (cm/s) compare ? 
(a)K>K(b)K<K(c)K~K
K(mol / (cm2)(sec.)(atm) ) and KL

285. Consider gas absorption with chemical reaction. The bulk liquid phase is the locals of reaction when the process conforms to – 
a) slow reaction regime
b) very slow reaction regime,
c) fast reaction regime,
d) instantaneous reaction regime

286. In the context of gas-liquid reaction, ÖM can be interpreted as a ratio of 
(a) (Reaction taking place in the film)/ (Reaction taking place in the bulk ) 
(b) (Diffusivity of gas (A)/ (Diffusivity of liquid reactant (B)) 
(c) (Reaction taking place in the bulk) / (Reaction taking place in the film as well as in bulk) 
(d) None of the foregoing. 
287. A certain gas-liquid reaction conforms to very slow reaction regime. For this case, the global rate is  kmol/m3 .s is 
(a) directly proportional to fractional liquid hold-up ;
(b) inversely proportional to fractional liquid hold-up ;
(c) directly proportional to the square of the fractional liquid hold-up
(d) inversely proportional to the square root of the fractional gas hold-up. 
288. In a gas-liquid system, the rate of gas absorption gets enhanced when the absorbent liquid reacts with the solute gas A. Now, for a gas absorption process conforming to slow reaction regime, the enhancement factor is 
a) ∞                 b) 100              c) 1                  d) 10
289. In order that a gas-liquid reaction conforms to fast-reaction regime, some conditions have to be satisfied. What are those conditions ? 
a) ÖM >> 3, ÖM << q ; b) ÖM << 1 ; ÖM >> q c) ÖM = 1 ; ÖM >> q (d) None of the above. 
290. In a gas-liquid reaction (A : gas ; B : liquid) conforming to instantaneous reaction regime, a reaction plane is formed where – 
a) [ A ] = 0 ; [ B ] ≠ 0 b) [ A ] = [ B ] = 0
c) [ A ] ≠ 0 ; [ B ] = 0 d) [ A ] ≠ 0 ; [ B ] ≠ 0 
291. A gas-liquid reaction conforms to the fast reaction regime. For this process, the enhancement factor is  
292. Consider a gas-liquid reaction; the intrinsic reaction rate is first order in A (gas) and first order in B (liquid). Experiments in jet apparatus with this system show that the global rate is independent of the concentration of A. What can you conclude from this observation ? 
(a) Absorption may conform to slow reaction regime
(b) It may conform to very slow reaction regime
(c) It may conform to fast reaction regime,
(d) It may conform to instantaneous reaction regime. 

293. Consider gas absorption with chemical reaction, intrinsic reaction rate = k [A] [B] . When the gas absorption conforms to fast reaction regime, the enhancement factor will be 
a) directly proportional to [A] 
b) directly proportional to [A]0.5 c) independent of A
d) independent of both A and B. 
294. For the above question, the global rate of absorption will be – 
(a) directly proportional to [ A ] and [ B ] 
(b) inversely proportional to [ A ], directly proportional to [ B ](c) independent of [ A] and [ B ], 
(d) directly proportional to [ A ] and [ B ]n/2 
295. A certain gas-absorption process conforms to the fast-reaction regime when the absorption is conducted in a plate column for which typical Kis 5 x 10-4 m/s. The enhancement factor is 10 and q = 40. If the absorption is conducted in a spray column for which typical K= 2 x 10-5 m/s; the absorption will be in
a) Fast reaction regime,
b) very slow reaction regime,
c) slow reaction regime,
d) instantaneous reaction regime 
296. Typical value of activation energy for gas absorption with chemical reaction conforming to fast reaction regime is – 
a) 100 kcal / mol or higher,
b) 10 – 20 kcal / mol
c) 4 – 6 kcal / mole
d) none of the foregoing 
297. Consider gas-absorption with chemical reaction. Experiment in a stirred cell shows that the rate of absorption is independent of the speed of stirring. The absorption conforms to 
a) show reaction regime
b) fast reaction regime
c) instantaneous reaction regime. 
298. Consider gas absorption with chemical reaction. The system conforms to the fast reaction regime. What is the bulk concentration of the solute gas in the absorbent liquid ? 
(a) equal to the solubility of the gas in the liquid at the corresponding temperature and pressure
(b) zero,
(c) a value which is less than the solubility of the gas in the liquid at the corresponding temperature and pressure 
(d) none of the foregoing. 
299. A certain gas absorption process conforms to instantaneous reaction regime. Under otherwise uniform conditions, if the gas phase partial pressure of the dissolving gas is doubled, the rate of absorption (kmol/m 3.s) will – 
a) increase by a factor of 2
b) increase by a factor of 
Ö2
c) decrease by a factor of 
Ö2
d) remain unchanged. 
300. Free fatty acids present in rice bran oil can be removed by contacting the oil with aqueous caustic soda solution. This is an example of liquid-liquid heterogeneous reaction. Without any other detail, what can you predict about the system ? 
a) conforms to very slow reaction regime
b) slow reaction regime
c) instantaneous reaction regime
d) fast reaction regime. 
301. Consider gas absorption with chemical reaction; absorption conforms to the instantaneous reaction regime. As the liquid phase reactant concentration is increased, what will happen to the position of the reaction plane ? Film thickness in the liquid side is δ 
a) will remain fixed at the same old position
b) will shift towards δ
c) will shift towards the gas-liquid interface
d) none of the foregoing. 
302. A gas absorption process conforms to fast reaction regime. For this case the specific rate of absorption will – 
(a) increase with an increase in interfacial turbulence
(b) decrease with an increase in interfacial turbulence
(c) be independent of interfacial turbulence. 
303. For conducting experiments on mass transfer with chemical reaction, it is customary to use model contractors. Name some model contractors used in gas absorption studies. 
304. In many desulfurization processes, H2S is absorbed in amine solutions. The system conforms to – 
a) slow reaction regime
b) fast reaction regime 

c) instantaneous reaction regime
d) very slow reaction regime. 
305. A gas-liquid reaction conforms to very slow reaction regime. This means - 
(a) the liquid phase is saturated with respect to the gas
(b) the bulk liquid phase concentration of the gas is zero
(c) part of the reaction takes place in the liquid film and part in the bulk (d) none of the foregoing is true. 
306. At low particle Reynolds number, the solid-liquid mass transfer coefficient will be 
a.     independent of the particle diameter
b.     directly proportional to the particle diameter
c.     inversely proportional to the particle diameter
d.     inversely proportional to the square root of the particle diameter 
307. Suppose we want to determine interfacial area of a gas-liquid contractor. For this the system chosen must conform to 
a) slow reaction regime
b) very slow reaction regime
c) fast reaction regime
d) instantaneous reaction regime. 
308. A certain gas absorption process conforms to instantaneous reaction regime. What is the enhancement factor for this case ? 
a) 1                  b) ÖM             c) q/ÖM          d) 1 + q 
309. Consider gas absorption with chemical reaction. Highest specific rte of absorption is realized when the absorption conforms to – 
a) slow reaction regime
b) fast reaction regime
c) instantaneous reaction regime 
310. For gas absorption with chemical reaction conforming to slow reaction regime, what is the bulk concentration of the solute gas A ? 
(a) equal to the solubility of the gas in the liquid at the corresponding temperature and pressure
(b) a concentration which is approximately half of the saturation solubility of the gas in the liquid at the corresponding temperature and pressure
(c) zero
(d) none of the foregoing.