Introduction: Filter aids MCQs With Answer are essential study resources for B.Pharm students preparing for pharmacognosy, pharmaceutics, and industrial pharmacy exams. This concise, Student-friendly guide focuses on filter aids such as diatomaceous earth (kieselguhr), perlite, cellulose, and activated carbon, covering properties, selection criteria, precoat and body-feed techniques, cake formation, filterability, specific cake resistance, and common filter equipment like tray, candle, rotary vacuum, and filter presses. Practical emphasis on pharmaceutical filtration, process optimization, health and safety (e.g., silicosis risk), and troubleshooting helps students master both theory and application. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the most commonly used filter aid in pharmaceutical filtration?
- Diatomaceous earth (kieselguhr)
- Perlite
- Cellulose powder
- Activated carbon
Correct Answer: Diatomaceous earth (kieselguhr)
Q2. Which property of a filter aid primarily increases filtration rate?
- High chemical reactivity
- Low bulk density
- High porosity and inertness
- High moisture content
Correct Answer: High porosity and inertness
Q3. In precoat filtration, the filter aid is applied as:
- A slurry added during the final wash
- A layer on the filter medium before filtration
- Mixed permanently with the active drug
- Sprayed onto the product after filtration
Correct Answer: A layer on the filter medium before filtration
Q4. Body-feed filtration involves:
- Applying the filter aid only to the filter cloth
- Adding filter aid to the feed slurry
- Heating the slurry to reduce viscosity
- Using only chemical coagulants
Correct Answer: Adding filter aid to the feed slurry
Q5. Which filter aid poses a health risk of silicosis if inhaled?
- Cellulose powder
- Diatomaceous earth containing crystalline silica
- Perlite
- Activated carbon
Correct Answer: Diatomaceous earth containing crystalline silica
Q6. Specific cake resistance in filtration is affected by:
- Color of the slurry
- Cake porosity and particle compressibility
- Ambient humidity only
- Container shape only
Correct Answer: Cake porosity and particle compressibility
Q7. Which equipment is best suited for continuous dewatering of large-volume suspensions?
- Laboratory Buchner funnel
- Rotary vacuum filter
- Small bench-top centrifuge
- Membrane dialyzer
Correct Answer: Rotary vacuum filter
Q8. Perlite as a filter aid is primarily used because of its:
- High density
- High thermal conductivity
- Low abrasiveness and good porosity
- Strong acidity
Correct Answer: Low abrasiveness and good porosity
Q9. The main purpose of adding filter aids to a slurry is to:
- Increase viscosity
- Provide a porous medium to retain fine solids
- React chemically with impurities
- Act as a preservative
Correct Answer: Provide a porous medium to retain fine solids
Q10. Which factor does NOT significantly affect filtration rate according to Darcy’s law?
- Viscosity of the filtrate
- Pressure drop across the cake
- Color of the cake
- Specific cake resistance
Correct Answer: Color of the cake
Q11. Kieselguhr is another name for which material?
- Perlite
- Diatomaceous earth
- Cellulose acetate
- Pumice
Correct Answer: Diatomaceous earth
Q12. Which filter aid is biodegradable and often used when chemical inertness is less critical?
- Activated carbon
- Cellulose powder
- Kieselguhr
- Perlite
Correct Answer: Cellulose powder
Q13. A compressible filter cake means:
- The cake expands under pressure
- Permeability decreases with increasing pressure
- Specific resistance remains constant
- The cake is chemically reactive
Correct Answer: Permeability decreases with increasing pressure
Q14. Which method is used to evaluate filterability of a slurry in the lab?
- pH titration
- Buchner funnel filtration and measuring filtrate volume vs time
- Melting point determination
- UV-Vis spectroscopy only
Correct Answer: Buchner funnel filtration and measuring filtrate volume vs time
Q15. Precoat filtration is preferred when:
- The solids are very coarse
- Fine or gelatinous solids would blind the cloth
- There is no need for clear filtrate
- Filtration is to be avoided altogether
Correct Answer: Fine or gelatinous solids would blind the cloth
Q16. In pharmaceutical filtration, filter aid selection should consider:
- Compatibility with product and solvents
- Only color of the aid
- Only supplier brand
- None of the above
Correct Answer: Compatibility with product and solvents
Q17. Which filter design uses flat plates and is suitable for batch operations?
- Rotary vacuum filter
- Filter press
- Membrane ultrafilter
- Continuous belt filter
Correct Answer: Filter press
Q18. Body feed is advantageous over precoat when:
- The product requires zero solids carryover
- Rapid initial filtration rate is not required
- Cost and simplicity are priorities and some entrainment is acceptable
- Filtrate must be completely sterile without any aid
Correct Answer: Cost and simplicity are priorities and some entrainment is acceptable
Q19. Which property of diatomaceous earth makes it effective as a filter aid?
- High solubility in water
- Porous siliceous skeleton and high surface area
- Magnetic properties
- Strong acidity
Correct Answer: Porous siliceous skeleton and high surface area
Q20. Activated carbon used as a filter aid primarily serves to:
- Increase cake strength
- Adsorb color and odor impurities
- Accelerate polymerization
- Raise boiling point of filtrate
Correct Answer: Adsorb color and odor impurities
Q21. Which test measures the resistance of a filter cake to flow?
- pH test
- Specific cake resistance measurement
- Melting point determination
- Spectral analysis
Correct Answer: Specific cake resistance measurement
Q22. When a filter cloth becomes blinded, it means:
- The cloth chemically dissolves
- Pores are clogged by fine particles reducing flow
- The cloth changes color
- The cloth increases in permeability
Correct Answer: Pores are clogged by fine particles reducing flow
Q23. The main disadvantage of using too much filter aid is:
- Improved filtrate clarity
- Increased product loss and cost
- Reduced cake dryness
- Enhanced chemical stability
Correct Answer: Increased product loss and cost
Q24. In pharmaceutical manufacturing, filter aids must be:
- Pharmacologically active
- Inert, non-toxic, and pharmacopeial grade where required
- Always organic
- Highly reactive with APIs
Correct Answer: Inert, non-toxic, and pharmacopeial grade where required
Q25. Which of the following is a mechanical method to improve cake washing?
- Changing pH of wash solvent only
- Pulse washing or displacement washing
- Adding more active drug
- Using only heat without solvent
Correct Answer: Pulse washing or displacement washing
Q26. Filtrate clarity is most directly influenced by:
- Color of container
- Particle size distribution and filter aid properties
- Brand of stirrer used
- Room lighting
Correct Answer: Particle size distribution and filter aid properties
Q27. Which filter aid is of volcanic origin and expanded by heating?
- Perlite
- Kieselguhr
- Activated carbon
- Cellulose
Correct Answer: Perlite
Q28. A cake with high porosity will generally have:
- Lower filtration rate
- Higher specific resistance
- Higher permeability and faster filtration
- Increased chemical reactivity
Correct Answer: Higher permeability and faster filtration
Q29. Which operation is used to remove residual mother liquor from the filter cake?
- Leaching
- Washing
- Centrifugation only
- Lyophilization
Correct Answer: Washing
Q30. Filter aids help protect filter cloth by:
- Reducing cake formation
- Forming a porous protective layer that prevents blinding
- Reacting with the filtrate chemically
- Dissolving the cloth slightly
Correct Answer: Forming a porous protective layer that prevents blinding
Q31. Which term describes the solid retained on the filter after filtration?
- Filtrate
- Permeate
- Filter cake
- Mother liquor
Correct Answer: Filter cake
Q32. Which parameter is reduced by using a precoat layer?
- Filtrate clarity
- Initial filtration rate
- Cloth blinding and fines breakthrough
- Filter surface area
Correct Answer: Cloth blinding and fines breakthrough
Q33. In Darcy’s law, flow rate is directly proportional to:
- Viscosity of liquid
- Pressure drop across the medium
- Specific cake resistance
- Cake thickness squared
Correct Answer: Pressure drop across the medium
Q34. Which of the following is NOT a desirable property of a filter aid?
- Chemical inertness with product
- High porosity
- Containment of toxic crystalline silica
- Good mechanical strength
Correct Answer: Containment of toxic crystalline silica
Q35. When is regenerative cleaning of filter cloth necessary?
- When cloth is brand new
- After repeated blinding and reduced permeability
- Only when color changes
- Never required in pharmaceutical operations
Correct Answer: After repeated blinding and reduced permeability
Q36. Which filter type uses candles or tubes for filtration?
- Rotary vacuum drum
- Candle filter (tubular filter)
- Plate and frame filter press
- Buchner funnel
Correct Answer: Candle filter (tubular filter)
Q37. A good pharmaceutical filter aid should be:
- Highly soluble
- Non-reactive and meet pharmacopeial specifications
- Strongly acidic
- Extremely magnetic
Correct Answer: Non-reactive and meet pharmacopeial specifications
Q38. Which cleaning method helps recover entrapped product from filter cake?
- Backwashing or reverse flow
- Ignition at high temperature
- Allowing cake to air dry only
- Increasing slurry viscosity
Correct Answer: Backwashing or reverse flow
Q39. In pharmaceutical filtration, cake dryness is important because:
- It increases dissolution time unnecessarily
- Residual solvent can affect stability and downstream processing
- It always makes product unusable
- It changes color only
Correct Answer: Residual solvent can affect stability and downstream processing
Q40. Which of the following reduces blinding most effectively?
- Removing filter aid altogether
- Using appropriate precoat or body-feed filter aid and correct particle size
- Using a smaller filter area only
- Reducing suspension temperature drastically
Correct Answer: Using appropriate precoat or body-feed filter aid and correct particle size
Q41. Which variable is typically measured to monitor filtration progress?
- Volume or mass of filtrate vs time
- Color of the operator’s gloves
- Ambient noise level
- Brand of filter aid used
Correct Answer: Volume or mass of filtrate vs time
Q42. Filter aid particle size affects:
- Only the color of filtrate
- Porosity, cake structure, and filtration rate
- Electrical conductivity of filtrate only
- Boiling point of slurry
Correct Answer: Porosity, cake structure, and filtration rate
Q43. Which filtration method is best to maintain sterility of the filtrate for heat-sensitive drugs?
- Precoat filtration with sterile filter aids and sterile conditions
- Open tray filtration in ambient air
- High-temperature drying before filtration
- Using unwashed filter cloth
Correct Answer: Precoat filtration with sterile filter aids and sterile conditions
Q44. What is a common consequence of cake channeling during washing?
- Uniform removal of mother liquor
- Incomplete washing and solvent entrapment
- Increased cake compressibility only
- Lowered filtrate conductivity intentionally
Correct Answer: Incomplete washing and solvent entrapment
Q45. Which analytical concern is addressed by using activated carbon as a filter aid?
- Particle size enlargement
- Removal of trace color and organic impurities
- Increase in specific cake resistance
- Reducing pH fluctuations
Correct Answer: Removal of trace color and organic impurities
Q46. What role does vacuum play in rotary vacuum filtration?
- It increases cake solubility
- It lowers boiling point only
- It provides driving force for filtrate removal across the cake
- It dissolves solids into liquid
Correct Answer: It provides driving force for filtrate removal across the cake
Q47. Which of the following improves cake permeability without changing cake composition?
- Compressing the cake more tightly
- Introducing coarser filter aid particles
- Reducing the filter area
- Removing all filter aid
Correct Answer: Introducing coarser filter aid particles
Q48. What is the main environmental concern with disposal of spent filter aids?
- They always explode
- Potential contamination with hazardous APIs or solvents
- They immediately biodegrade harmlessly
- They become highly radioactive
Correct Answer: Potential contamination with hazardous APIs or solvents
Q49. Which parameter is decreased by increasing the pressure drop across a filter cake (for incompressible cakes)?
- Filtration rate (for incompressible cakes, rate increases with pressure)
- Filtration rate (it always decreases)
- Permeability of cake regardless of compressibility
- None; filtration is independent of pressure
Correct Answer: Filtration rate (for incompressible cakes, rate increases with pressure)
Q50. When selecting a filter aid for an organic solvent system, the key requirement is:
- High water solubility
- Chemical compatibility and inertness in that solvent
- Ability to react with solvent
- High magnetic susceptibility
Correct Answer: Chemical compatibility and inertness in that solvent
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