Syspensions

Question 1

1. According to Stokes’ law, which change MOST effectively decreases sedimentation rate in a suspension?
   A. Increasing particle size
   B. Decreasing viscosity
   C. Increasing viscosity of the continuous phase
   D. Increasing density difference

Answer 1

C

Question 2

2. A suspension shows rapid settling but no caking. This indicates:
   A. Very high zeta potential
   B. Deflocculated system
   C. Flocculated system
   D. Excessive viscosity

Answer 2

C

Question 3

3. Why does decreasing particle size reduce sedimentation rate?
   A. It increases density
   B. It reduces gravitational force effect
   C. It increases interparticle attraction
   D. It increases solubility

Answer 3

B

Question 4

4. A high-density drug dispersed in a low-density vehicle will:
   A. Settle faster
   B. Show upward creaming
   C. Become deflocculated
   D. Become more stable

Answer 4

A

Question 5

5. Brownian motion dominates when particles are:
   A. > 5 µm
   B. < 2 µm
   C. > 50 µm
   D. In a highly viscous vehicle only

Answer 5

B

Question 6

6. A suspension shows extremely slow settling but forms a hard, compact cake. This behavior is typical of:
   A. Controlled flocculation
   B. Deflocculated systems
   C. Flocculated systems
   D. Ostwald ripening

Answer 6

B

Question 7

7. Which factor does NOT significantly affect sedimentation rate?
   A. Particle density
   B. Continuous phase viscosity
   C. Surface charge
   D. Particle size

Answer 7

C

Question 8

8. A suspension has very high zeta potential. This suggests particles will be:
   A. Highly flocculated
   B. Strongly repelling → deflocculated
   C. Rapidly settling without caking
   D. Unstable under all conditions

Answer 8

B

Question 9

9. Adding a small amount of electrolyte to a deflocculated suspension often results in:
   A. Intensified repulsion
   B. Compression of electric double layer → flocculation
   C. Rapid dissolution
   D. Increase in pH

Answer 9

B

Question 10

10. Controlled flocculation aims to:
    A. Eliminate settling
    B. Create loose, high-volume sediment that is easy to redisperse
    C. Create a tight cake
    D. Maximize zeta potential

Answer 10

B

Question 11

11. In DLVO theory, the primary minimum represents:
    A. A reversible energy well
    B. Irreversible coagulation region
    C. Maximum repulsive energy barrier
    D. Non-settling region

Answer 11

B

Question 12

12. The secondary minimum in DLVO theory corresponds to:
    A. Weak, reversible flocculation
    B. Strong, irreversible caking
    C. Complete repulsion
    D. Permanent aggregation

Answer 12

A

Question 13

13. Reducing zeta potential too much causes:
    A. Deflocculation
    B. Cake formation
    C. Increased viscosity
    D. Zero sedimentation

Answer 13

B

Question 14

14. Degree of flocculation (β) compares:
    A. Sedimentation height in flocculated vs deflocculated systems
    B. Particle size before and after flocculation
    C. Electrolyte concentration and viscosity
    D. Surface charge and ion concentration

Answer 14

A

Question 15

15. A suspension shows an F value (sedimentation volume) of 1.0. This means:
    A. System cracked
    B. No settling occurred (ideal flocculation)
    C. System is fully deflocculated
    D. Vehicle is supersaturated

Answer 15

B

Question 16

16. A flocculated suspension usually has:
    A. Low sedimentation volume
    B. High sedimentation volume
    C. Zero sedimentation
    D. High viscosity only

Answer 16

B

Question 17

17. If β increases, this indicates:
    A. Better floc formation
    B. Poor redispersion
    C. Stronger particle repulsion
    D. Increased particle size

Answer 17

A

Question 18

18. High sedimentation height but easy redispersion suggests:
    A. Controlled flocculation
    B. Ostwald ripening
    C. Deflocculated system
    D. Agglomeration

Answer 18

A

Question 19

19. A poorly wetting hydrophobic drug powder is best addressed by adding:
    A. Thickening agents
    B. Wetting agents (surfactants)
    C. Electrolytes
    D. Antifoaming agents

Answer 19

B

Question 20

20. Wetting agents improve dispersion by:
    A. Increasing particle size
    B. Decreasing interfacial tension
    C. Removing electrolytes
    D. Increasing viscosity

Answer 20

B

Question 21

21. A suspension with poor initial dispersion likely suffers from:
    A. Low zeta potential
    B. High interfacial tension
    C. High degree of flocculation
    D. Excessive viscosity

Answer 21

B

Question 22

22. Ostwald ripening occurs because:
    A. Small crystals dissolve and redeposit on larger crystals
    B. Large particles spontaneously shrink
    C. Polymers adsorb onto surfaces
    D. Viscosity is too high

Answer 22

A

Question 23

23. Ostwald ripening is accelerated when:
    A. Solubility difference between particle sizes is high
    B. Particles are spherical
    C. The suspension is flocculated
    D. Zeta potential is high

Answer 23

A

Question 24

24. Crystal growth in suspensions leads to:
    A. Improved uniformity
    B. Caking due to tightly packed particles
    C. Increased redispersibility
    D. Reduced sedimentation volume

Answer 24

B

Question 25

25. Suspending agents prevent caking primarily by: A. Increasing viscosity B. Decreasing surface tension C. Increasing particle density D. Dissolving particles

Answer 25

A

Question 26

26. Adding too much polymeric suspending agent results in: A. Rapid settling B. Excessively high viscosity and poor pourability C. Deflocculation D. Ostwald ripening

Answer 26

B

Question 27

27. Density matching in suspensions is done to: A. Increase zeta potential B. Reduce sedimentation rate C. Improve wetting D. Prevent phase inversion

Answer 27

B

Question 28

28. The ideal rheological behavior for suspensions is: A. Newtonian flow B. Thixotropic plastic flow C. Dilatant flow D. Zero-shear viscosity

Answer 28

B

Question 29

29. Thixotropy benefits suspensions because it: A. Makes them solid B. Decreases viscosity upon shaking and reforms structure at rest C. Increases sedimentation D. Causes irreversible aggregation

Answer 29

B

Question 30

30. A suspension that becomes more viscous upon mixing exhibits: A. Thixotropy B. Dilatancy C. Plasticity D. Newtonian flow

Answer 30

B

Question 31

31. Temperature cycling causes instability because: A. Zeta potential increases B. Solubility changes promote crystal growth C. Viscosity stays constant D. Particles melt

Answer 31

B

Question 32

32. A suspension stored at high temperatures may show: A. Lower solubility → crystallization B. Improved stability C. Reduced diffusion D. More repulsion

Answer 32

A

Question 33

33. Freezing a suspension is risky because: A. Particles dissolve B. Ice crystals disrupt particle arrangement → caking C. Flocculation increases D. Viscosity becomes too low

Answer 33

B

Question 34

34. Suspensions are preferred for pediatric dosing primarily because: A. They have no taste B. They allow flexible dosing of insoluble drugs C. They prevent all side effects D. They never settle

Answer 34

B

Question 35

35. For a poorly soluble drug requiring high dose per mL, the BEST strategy is: A. Deflocculation B. Controlled flocculation with viscosity enhancement C. Replace with solution D. Decrease particle density

Answer 35

B

Question 36

36. Bioavailability of a drug from suspension increases when: A. Particle size decreases → increased dissolution B. Sedimentation rate increases C. Caking occurs D. Viscosity is extremely high

Answer 36

A

Question 37

37. The main cause of caking in suspensions is: A. High zeta potential B. Formation of a compact crystal network at the bottom C. Excessive flocculation D. Too much wetting agent

Answer 37

B

Question 38

38. Poor redispersibility indicates: A. Correct floc strength B. Strong irreversible particle aggregation C. Low solubility D. Good stability

Answer 38

B

Question 39

39. A suspension forms a large sediment height but resuspends with light shaking. This indicates: A. Deflocculation B. Controlled flocculation C. Coagulation D. Zero zeta potential

Answer 39

B

Question 40

40. A formulation shows sedimentation volume F = 0.2. This suggests: A. Highly flocculated B. Strongly deflocculated with tight sediment C. No sedimentation D. Equilibrium flocs

Answer 40

B

Question 41

41. A suspension becomes less stable upon adding electrolytes because: A. Zeta potential increases B. Zeta potential collapses → aggregation C. Viscosity becomes zero D. Diffusion decreases

Answer 41

B

Question 42

42. A hydrophobic drug shows floating particles after shaking. The MOST likely cause is: A. Too much viscosity B. Poor wetting C. Excessive electrolyte D. Large density difference

Answer 42

B

Question 43

43. High polymer concentration causes a “false stability” because: A. Particles dissolve B. Sedimentation is slowed but caking risk remains if flocculation is poor C. Zeta potential becomes zero D. Ostwald ripening accelerates

Answer 43

B

Question 44

44. In a well-formulated flocculated suspension, particles settle quickly because: A. They are large clusters with high sedimentation velocity B. They are too dense C. Viscosity is low D. Repulsive forces dominate

Answer 44

A

Question 45

45. The MOST stable system against long-term caking is: A. Strongly deflocculated B. Controlled flocculated + increased viscosity C. Large particle size D. Zero charge (coagulated)

Answer 45

B