Effective mixing is a foundational unit operation in pharmaceutics, vital for B.Pharm students who design, develop and evaluate formulations. Applications of mixing include achieving uniform drug distribution, enhancing dissolution, preparing granules, emulsions and suspensions, and ensuring content uniformity for tablets and capsules. Understanding equipment—ribbon blenders, V‑blenders, high-shear mixers, homogenizers—and parameters like mixing time, impeller type, shear rate, and scale-up criteria helps prevent segregation, assure quality, and meet regulatory assays. This keyword-rich overview emphasizes practical mixing applications, formulation troubleshooting, validation, and blend uniformity assessment, preparing students for exams and industry practice. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the primary purpose of mixing in a pharmaceutical powder formulation?
- To reduce particle size
- To achieve homogenous distribution of components
- To sterilize the powder
- To change chemical structure
Correct Answer: To achieve homogenous distribution of components
Q2. Which mixer is commonly used for free-flowing powder blends at large scale?
- High-shear granulator
- V‑blender
- Colloid mill
- Rotor-stator mixer
Correct Answer: V‑blender
Q3. Which mixing mechanism predominates in tumbling blenders like V‑blenders?
- Shear mixing
- Diffusive mixing
- Convective mixing
- Ultrasonic mixing
Correct Answer: Convective mixing
Q4. What is a common problem when mixing powders with very different particle sizes and densities?
- Improved dissolution
- Segregation
- Enhanced homogeneity
- Increased wettability
Correct Answer: Segregation
Q5. Which parameter is most directly used to determine mixing time for a blender?
- Power consumption only
- Sampling and assay for content uniformity
- Rotor speed without sampling
- Particle size distribution measurement only
Correct Answer: Sampling and assay for content uniformity
Q6. Which equipment is preferred for wet granulation that requires high shear?
- Ribbon blender
- High-shear granulator (planetary mixer)
- V‑blender
- Static mixer
Correct Answer: High-shear granulator (planetary mixer)
Q7. What is the effect of adding baffles to a stirred tank during liquid mixing?
- Decrease turbulence and promote vortex formation
- Increase vortex formation
- Suppress vortex and improve axial mixing
- Eliminate shear entirely
Correct Answer: Suppress vortex and improve axial mixing
Q8. Which impeller type is commonly used for low-viscosity liquid mixing?
- Anchor impeller
- Paddle impeller
- Rushton turbine
- Propeller (marine) impeller
Correct Answer: Propeller (marine) impeller
Q9. The Power number (Np) of an impeller is used to relate power consumption to which of the following?
- Vessel temperature
- Impeller speed and diameter
- pH of solution
- Viscosity only
Correct Answer: Impeller speed and diameter
Q10. Which mixing approach reduces particle agglomeration in suspensions?
- Using only tumbler blenders
- Applying appropriate shear and dispersing agents
- Mixing at very low temperature
- Omitting wetting agents
Correct Answer: Applying appropriate shear and dispersing agents
Q11. What is the main advantage of a ribbon blender for dry powder mixing?
- High shear for granulation
- Efficient gentle convective mixing for free-flowing powders
- Steam sterilization capability
- Best for highly cohesive powders
Correct Answer: Efficient gentle convective mixing for free-flowing powders
Q12. During scale-up of a mixing process, which criterion commonly preserves mixing conditions?
- Maintaining geometric similarity only
- Constant power per unit volume (P/V)
- Maintaining same impeller diameter only
- Using same blender brand
Correct Answer: Constant power per unit volume (P/V)
Q13. Which mixing index quantifies homogeneity of a blend?
- Viscosity index
- Segregation index
- Coefficient of variation (CV) or relative standard deviation (RSD)
- pH stability index
Correct Answer: Coefficient of variation (CV) or relative standard deviation (RSD)
Q14. In liquid-liquid mixing for emulsions, which equipment is most appropriate for fine droplet size?
- Mortar and pestle
- High-pressure homogenizer or rotor-stator homogenizer
- V‑blender
- Ribbon blender
Correct Answer: High-pressure homogenizer or rotor-stator homogenizer
Q15. What causes percolation segregation in powder mixes?
- Electrostatic attraction
- Smaller particles moving downward through voids between larger particles
- Chemical incompatibility
- Excessive moisture
Correct Answer: Smaller particles moving downward through voids between larger particles
Q16. Which technique helps reduce segregation after mixing when filling capsules?
- Rapid vibration during filling
- Use of granulation or binders to enlarge particle size
- Cooling the powder below room temperature
- Adding salts to increase density
Correct Answer: Use of granulation or binders to enlarge particle size
Q17. What is the main role of a deaeration step after wet mixing in granulation?
- Increase porosity
- Remove trapped air to improve compactibility and uniformity
- Reduce moisture content to zero
- Sterilize the granules
Correct Answer: Remove trapped air to improve compactibility and uniformity
Q18. Which parameter increases with higher impeller speed during liquid mixing?
- Mixing time always increases
- Shear rate and turbulent intensity
- Viscosity of the fluid
- pH of the solution
Correct Answer: Shear rate and turbulent intensity
Q19. In laminar mixing regimes for viscous fluids, which mechanism dominates mixing?
- Turbulent eddy diffusion
- Convective bulk flow only
- Viscous diffusion and chaotic advection
- Surface evaporation
Correct Answer: Viscous diffusion and chaotic advection
Q20. What is a common analytical method to assess powder blend uniformity?
- Assay of active pharmaceutical ingredient (API) in multiple samples
- Measuring bulk density only
- Visual inspection
- Measuring color intensity only
Correct Answer: Assay of active pharmaceutical ingredient (API) in multiple samples
Q21. Which mixer is best for forming dispersions and emulsions at laboratory scale?
- V‑blender
- Rotary drum
- Rotor-stator homogenizer (high-shear mixer)
- Cone blender
Correct Answer: Rotor-stator homogenizer (high-shear mixer)
Q22. When mixing heat-sensitive APIs in liquid formulations, what is a crucial consideration?
- Maximizing shear regardless of temperature rise
- Controlling temperature rise due to shear and using cooling
- Using only metal impellers to increase heat
- Avoiding any surfactants
Correct Answer: Controlling temperature rise due to shear and using cooling
Q23. What does bulk density heterogeneity after mixing indicate?
- Perfect mixing
- Possible segregation or incomplete mixing
- Sterilization success
- Correct moisture content
Correct Answer: Possible segregation or incomplete mixing
Q24. Which of the following promotes distributive mixing in powders?
- Vibration without rotation
- Layering and rotation that interchange particle positions
- Only increasing temperature
- Leaving powders static for long time
Correct Answer: Layering and rotation that interchange particle positions
Q25. In blender validation, what is a typical acceptance criterion for blend uniformity?
- RSD or CV less than a specified percentage (e.g., <5–10%)
- Bulk density change of 50%
- Visual uniformity only
- pH within ±3 units
Correct Answer: RSD or CV less than a specified percentage (e.g., <5–10%)
Q26. Which mixer type is most suitable for highly viscous semi-solid formulations?
- Propeller impeller only
- Planetary or anchor mixers designed for high viscosity
- V‑blender
- Colloid mill at low speed
Correct Answer: Planetary or anchor mixers designed for high viscosity
Q27. What is shear-thinning behavior and why is it relevant to mixing?
- Viscosity increases with shear; irrelevant
- Viscosity decreases with shear; affects mixing energy and scale-up
- Viscosity remains constant with shear; affects pH
- Solution becomes solid at high shear
Correct Answer: Viscosity decreases with shear; affects mixing energy and scale-up
Q28. Which factor does NOT directly affect powder mixing efficiency?
- Particle size distribution
- Moisture content
- API chemical stability under light
- Particle shape and surface properties
Correct Answer: API chemical stability under light
Q29. During wet granulation, what is the role of binder solution distribution?
- Reduce density variations only
- Promote agglomeration to form granules and improve flow
- Increase segregation
- Neutralize APIs chemically
Correct Answer: Promote agglomeration to form granules and improve flow
Q30. What is the purpose of impeller clearance from the tank bottom during liquid mixing?
- To prevent heating
- To avoid dead zones and improve circulation
- To increase vortex depth
- To immobilize solids
Correct Answer: To avoid dead zones and improve circulation
Q31. Which dimensionless number helps predict flow regime in mixing (laminar vs turbulent)?
- Reynolds number
- pH number
- Viscosity index
- Blend uniformity number
Correct Answer: Reynolds number
Q32. What mixing strategy minimizes dust generation during powder blending?
- Mix at very high speeds without enclosures
- Use closed systems with appropriate inlet/outlet control
- Remove lids frequently
- Increase ambient temperature drastically
Correct Answer: Use closed systems with appropriate inlet/outlet control
Q33. Which mixer is most appropriate for small-batch laboratory blending of powders?
- Industrial V‑blender only
- Planetary mixer or small lab tumbling blender
- Full-scale high-pressure homogenizer
- Large ribbon blender
Correct Answer: Planetary mixer or small lab tumbling blender
Q34. How does moisture content influence powder mixing?
- It always improves flowability
- It can cause agglomeration and change flow, affecting blend uniformity
- It has no effect on mixing
- It sterilizes the powder
Correct Answer: It can cause agglomeration and change flow, affecting blend uniformity
Q35. Which analytical technique can map spatial distribution of API in a blend non-destructively?
- Near-infrared (NIR) imaging or Raman mapping
- Bulk density measurement only
- UV-visible colorless assay
- Thermogravimetric analysis only
Correct Answer: Near-infrared (NIR) imaging or Raman mapping
Q36. What is the effect of overmixing a brittle powder blend?
- Improved particle integrity
- Potential particle attrition and generation of fines leading to segregation
- Increased homogeneity always
- Complete sterilization
Correct Answer: Potential particle attrition and generation of fines leading to segregation
Q37. Which term describes mixing by layers sliding over one another in tumbling blenders?
- Diffusion
- Convection
- Shear-induced layering (or convective layering)
- Osmosis
Correct Answer: Shear-induced layering (or convective layering)
Q38. For cohesive powders that tend to lump, which approach improves mixing?
- Reduce binder use
- Add glidants, modify moisture or use intensive mixers to break agglomerates
- Only increase mixing speed without other changes
- Store at very low humidity without mixing
Correct Answer: Add glidants, modify moisture or use intensive mixers to break agglomerates
Q39. What is the role of a chute or feed design when discharging powders from a blender?
- To increase segregation
- To ensure smooth discharge and minimize segregation during transfer
- To heat the powder before packaging
- Only to provide structural support
Correct Answer: To ensure smooth discharge and minimize segregation during transfer
Q40. Which factor is critical when choosing a mixer for sterile liquid pharmaceutical formulations?
- Electrical color
- Ability to be cleaned and sterilized (CIP/SIP compatibility)
- Number of operators required
- Ambient light level
Correct Answer: Ability to be cleaned and sterilized (CIP/SIP compatibility)
Q41. What is the typical consequence of dead zones in a mixing vessel?
- Enhanced mixing efficiency
- Local concentration gradients and poor homogeneity
- Automatic sterilization
- Reduced viscosity uniformly
Correct Answer: Local concentration gradients and poor homogeneity
Q42. In solid-liquid mixing for suspensions, what reduces sedimentation rate?
- Decreasing viscosity
- Increasing medium viscosity or using suspending agents
- Reducing particle size to macroscopic scale
- Removing surfactants
Correct Answer: Increasing medium viscosity or using suspending agents
Q43. What is the key advantage of continuous mixing processes over batch mixing?
- Less control over residence time
- Better consistency and scalability for some processes with steady-state operation
- Higher risk of contamination always
- Impossible to validate
Correct Answer: Better consistency and scalability for some processes with steady-state operation
Q44. Which mixing assessment metric is used in Process Analytical Technology (PAT) for real-time monitoring?
- Offline HPLC only
- NIR spectroscopy or other inline sensors
- Only visual checks
- Thermal gravimetric offline tests only
Correct Answer: NIR spectroscopy or other inline sensors
Q45. What mixing strategy is recommended when incorporating a potent API at very low concentration?
- Directly add to final large blend without precautions
- Use ordered mixing or stepwise dilution (e.g., geometric dilution) to ensure uniformity
- Mix only by hand
- Avoid mixing and compress directly
Correct Answer: Use ordered mixing or stepwise dilution (e.g., geometric dilution) to ensure uniformity
Q46. Which phenomenon describes re-segregation after initially uniform mixing when vibrated?
- Enhanced mixing
- De-mixing or segregation due to vibration
- Chemical reaction
- Complete dissolution
Correct Answer: De-mixing or segregation due to vibration
Q47. For foam or aerated formulations, what mixing control is essential?
- Maximizing air entrainment always
- Controlling shear and aeration to achieve desired bubble size and stability
- Eliminating surfactants
- Only using static mixers
Correct Answer: Controlling shear and aeration to achieve desired bubble size and stability
Q48. Which inlet addition technique improves uniform distribution of a liquid binder onto a powder bed?
- Adding binder only at the end of mixing
- Spray addition with controlled spray nozzle across the bed
- Pipetting large droplets in single spot
- Heating binder in bulk before addition
Correct Answer: Spray addition with controlled spray nozzle across the bed
Q49. What is the main consideration when sampling a powder blend for uniformity testing?
- Sampling only from the center of the blender
- Representative, statistically valid sampling from multiple locations
- Taking a single large sample from discharge only
- Sampling after sieving only
Correct Answer: Representative, statistically valid sampling from multiple locations
Q50. Which corrective action is appropriate if blend uniformity fails acceptance criteria during validation?
- Ignore and continue production
- Investigate root cause, adjust mixing parameters or formulation, and revalidate
- Reduce sampling frequency
- Change assay method arbitrarily
Correct Answer: Investigate root cause, adjust mixing parameters or formulation, and revalidate
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
Mail- Sachin@pharmacyfreak.com