Free Mass Transfer Operations MCQs with Answers

• A. Cresylic acid
• B. Sodium carbonate
• C. Calcium carbonate
• D. Copper sulphate

Explanation: Copper sulphate is a classic activator in froth flotation, especially for activating sphalerite so it can respond to collectors.

• A. Continuously decreases
• B. Continuously increases
• C. Remain constant throughout
• D. May increase or decrease; depends on the pressure

Explanation: At constant pressure, the growing filter cake adds resistance to flow as filtration proceeds, so the filtrate flow rate continuously…

• A. Coagulation
• B. Sedimentation
• C. Flocculation
• D. Clarification

Explanation: Sedimentation uses gravity to separate a suspension into a clear supernatant and a concentrated, denser slurry.

• A. Carbonates
• B. Sulphates
• C. Bi-carbonates
• D. Silicates & phosphates

Explanation: Silicates and phosphates commonly act as dispersants by giving particles like charges and reducing their tendency to form flocs.

• A. Perforated horizontal basket continuous
• B. Disc-bowl
• C. Tubular bowl
• D. Suspended batch basket

Explanation: A continuous perforated horizontal-basket centrifuge, commonly a pusher-type centrifuge, is suited to relatively strong, non-friable…

• A. Dew point
• B. Bubble point
• C. Dry bulb temperature
• D. Wet bulb temperature

Explanation: The dew point is reached when a gas-vapour mixture becomes saturated during cooling at constant pressure without liquid contact.

• A. Increased efficiency
• B. High operating cost
• C. Decreased efficiency
• D. Better gas liquid contact

Explanation: A high absorber pressure drop requires greater gas-side pumping or compression work, increasing operating cost.

• A. 10-9 cm/sec
• B. 10-3 sec/cm
• C. 10-1 cm2/sec
• D. 10-4 cm2/sec2

Explanation: Gas molecules diffuse relatively rapidly, giving binary diffusivities of about 0.1 cm²/s at atmospheric pressure.

• A. Increases
• B. Exponentially increases
• C. Does not affect
• D. Decreases

Explanation: Case hardening forms a dry, relatively impermeable outer shell that resists the movement of internal moisture to the surface.

• A. Tray
• B. Tunnel
• C. Conveyor
• D. Festoon

Explanation: Refractory bricks are bulky and require controlled, gradual drying, for which a tunnel dryer provides continuous passage through heated…

• A. Cross-partition
• B. Lessing
• C. Raschig
• D. Single spiral

Explanation: Raschig rings are the traditional and most widely used random packing in industrial gas absorption and stripping equipment.

• A. rpm
• B. Inclination with ground surface
• C. Neither A. nor B.
• D. Both A. and B.

Explanation: Rotary-dryer capacity is affected by rotational speed and drum inclination, since both determine solids residence time and the cascading…

• A. Oxidising atmosphere
• B. SO2
• C. H2SO4
• D. Alkalis

Explanation: Carbon packing has good resistance to many acids and alkalis but can be attacked or consumed in an oxidising atmosphere.

• A. 1-5
• B. 10-60
• C. 200-300
• D. > 500

Explanation: Spray dryers atomize the feed into fine droplets, commonly in the approximate 10 to 60 micrometre range, giving a very large surface area…

• A. Always < 1
• B. G/L
• C. L/G
• D. None of these

Explanation: For an absorber with insoluble gas and non-volatile solvent, the operating-line slope on a solute-free basis is L/G.

• A. Stanton
• B. Sherwood
• C. Peclet
• D. Schmidt

Explanation: The Schmidt number, Sc = ν/D, compares momentum diffusivity with mass diffusivity, just as the Prandtl number compares momentum…

• A. An irreversible phenomenon
• B. Both B. and C.
• C. Accompanied by evolution of heat
• D. A reversible phenomenon

Explanation: Physical absorption involves intermolecular dissolution rather than chemical reaction, so it is generally reversible and releases heat…

• A. Absorption
• B. Extraction
• C. Adsorption
• D. Leaching

Explanation: Ion exchange involves the reversible replacement of ions between a liquid and an insoluble solid, much like adsorption in which solute…

• A. Separation becomes more efficient
• B. None of these
• C. Column diameter increases
• D. Number of plates increases

Explanation: Lowering the reflux ratio reduces the liquid returned to the column and weakens separation per stage, so more theoretical plates are…

• A. Increases
• B. Remains unchanged
• C. Decreases
• D. Decreases linearly

Explanation: Dew point is the temperature at which the existing water vapour becomes saturated.