Free Mass Transfer Operations MCQs with Answers

• A. Fick's second law of diffusion
• B. Steady state diffusion for stagnant case
• C. Liquid M.T.C. by Higbie penetration theory
• D. None of these

Explanation: The factor P_t/P_BM is characteristic of diffusion of A through stagnant, non-diffusing B, while the concentration driving force appears…

• A. Remain unaffected
• B. Decrease
• C. Increase
• D. Decrease or increase; depends on the type of liquid

Explanation: Reducing the liquid flow lowers the liquid-to-gas ratio and generally reduces the absorption driving force for the same required…

• A. Mixture of two gases
• B. Sparingly soluble gas
• C. Ideal gas
• D. Pure gas

Explanation: Co-current absorption is commonly used when the gas is essentially pure, because the entering streams then provide a large concentration…

• A. 2.0
• B. 1.56
• C. 1.0
• D. 0.56

Explanation: Using x=(y-0.001)/5, the equilibrium gas concentration is y*=1.5x=0.3(y-0.001). Integration gives NOG≈5.09, so Z=HOGNOG=0.4×5.09≈2.0 m.

• A. Spouted bed
• B. Tray
• C. Rotary
• D. Truck

Explanation: Rotary dryers are suited to continuous, large-scale drying of free-flowing solids such as sugar because they provide high throughput and…

• A. At a fixed temperature
• B. Soluble in the liquid
• C. Non-ideal in nature
• D. Insoluble in the liquid

Explanation: Humidification transfers vapor from a pure liquid into a fixed, usually noncondensable gas that is insoluble or nearly insoluble in the…

• A. Surface evaporation of unbound moisture occurs
• B. Increasing the air temperature decreases the drying rate
• C. Increased air humidity decreases the rate of drying
• D. None of these

Explanation: During the constant-rate period, evaporation occurs from a continuously wet surface, mainly involving unbound moisture.

• A. Sand filter
• B. Reverse osmosis
• C. Lime soda
• D. Permutit

Explanation: Reverse osmosis uses pressure to force water through a semipermeable membrane while rejecting dissolved salts.

• A. Increase the rate of absorption
• B. Reduce the cooling water circulation rate
• C. Avoid corrosion
• D. None of these

Explanation: Keeping HCl gas above its dew point prevents condensation of acidic moisture on equipment surfaces, thereby reducing corrosion.

• A. Reduction
• B. Nitration
• C. Desorption
• D. Combustion

Explanation: Desorption is a unit operation because a dissolved component is transferred from a liquid phase into a gas phase.

• A. Separation of isotopes of uranium from gaseous uranium hexafluoride
• B. Separation of helium from natural gas
• C. Purification of oxygen
• D. Desalination of brackish water to produce potable (drinking) water

Explanation: Reverse osmosis forces water through a semipermeable membrane while retaining dissolved salts, so it is widely used to desalinate brackish…

• A. Dilute H2SO4
• B. Ethanol amine
• C. Chilled water
• D. Tri-butyl phosphate

Explanation: Hydrogen sulphide is an acidic gas and is readily absorbed by aqueous ethanolamine solutions such as MEA or DEA, which can later be…

• A. Osmosis
• B. Absorption
• C. Reverse osmosis
• D. Adsorption

Explanation: Reverse osmosis uses pressure greater than the osmotic pressure to force water through a semipermeable membrane while retaining most…

• A. NaOH
• B. Alum solution
• C. Hydrazine
• D. H2SO4

Explanation: A cation exchanger replaces positive ions with hydrogen ions during regeneration, so a strong acid such as H₂SO₄ is used.

• A. Extraction with amyl or butyl acetate
• B. Ternary Azeotropic distillation
• C. Evaporator in calandria
• D. Extractive distillation

Explanation: Penicillin is recovered from the broth by solvent extraction, commonly using amyl acetate or butyl acetate after adjusting the pH.

• A. SO3 gas is sparingly soluble in water
• B. Water forms an acid mist, which is difficult to absorb
• C. The purity of acid is affected
• D. Scale formation in the absorber is to be avoided

Explanation: Absorbing SO₃ directly in water produces a fine sulphuric-acid mist that is difficult to collect and causes loss of product.

• A. PCl5
• B. CaCl2
• C. Quick lime
• D. Concentrated H2SO4

Explanation: Quicklime, CaO, removes moisture from ammonia without reacting appreciably with the gas.

• A. Exchange between a liquid phase and an organic resin phase
• B. Exchange between a gaseous phase and a liquid phase
• C. Exchange between two liquid phases
• D. Exchange between a solid phase and a gas phase

Explanation: Ion exchange removes dissolved ions by contacting the leach liquor with an insoluble organic resin containing exchangeable ions.

• A. Freeze drying
• B. Solar evaporation
• C. Electrolytic
• D. None of these

Explanation: Sea water is spread in shallow salt pans, where solar heat evaporates water and leaves sodium chloride crystallised.

• A. Partial pressure of water vapour is less than the total pressure
• B. Humidity is < 100% & dew point temperature of air has not reached
• C. Air is fully saturated
• D. Dew point temperature of air has not reached & air is not saturated fully

Explanation: Wet-bulb depression becomes zero when evaporation from the wet bulb is no longer possible, which occurs at 100% relative humidity.