Effect of electrolytes on colloids MCQs With Answer

Understanding the effect of electrolytes on colloids is essential for B. Pharm students focusing on drug formulations and suspension stability. This concise overview explains how electrolyte concentration, ion valency and specific ion adsorption alter colloidal stability through zeta potential modulation, ionic strength effects and DLVO interactions. Key topics include the Schulze–Hardy rule, critical coagulation concentration (CCC), charge neutralization, electrostatic versus steric stabilization, and practical measurement of zeta potential. These MCQs reinforce theory, calculations and laboratory interpretation for exam readiness. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary effect of adding electrolytes to a lyophobic colloidal suspension?

• Increase in steric stabilization
• Compression of the electrical double layer
• Formation of covalent bonds between particles
• Increase in particle solubility

Correct Answer: Compression of the electrical double layer

Q2. According to the Schulze–Hardy rule, which ion is most effective at causing coagulation of a negatively charged colloid?

• Monovalent cation
• Divalent cation
• Trivalent cation
• Any anion regardless of valency

Correct Answer: Trivalent cation

Q3. What does CCC stand for in colloid chemistry?

• Critical Coagulation Concentration
• Colloid Charge Coefficient
• Critical Colloid Conductivity
• Coagulation Current Constant

Correct Answer: Critical Coagulation Concentration

Q4. Zeta potential is best described as:

• The total charge of a particle including all adsorbed ions
• The potential at the slipping plane related to particle mobility
• The electrostatic potential at the particle core
• The van der Waals attraction between particles

Correct Answer: The potential at the slipping plane related to particle mobility

Q5. How does increasing ionic strength generally affect the Debye length (κ⁻¹)?

• Debye length increases
• Debye length decreases
• Debye length becomes infinite
• Debye length is unaffected by ionic strength

Correct Answer: Debye length decreases

Q6. Which interaction pair constitutes the DLVO theory?

• Hydrophobic and hydrophilic forces
• Electrostatic repulsion and van der Waals attraction
• Steric repulsion and depletion attraction
• Covalent bonding and hydrogen bonding

Correct Answer: Electrostatic repulsion and van der Waals attraction

Q7. What is the usual practical zeta potential magnitude (approx.) considered indicative of colloidal stability?

• Less than ±5 mV
• Around ±15 mV
• Greater than ±30 mV
• Exactly 0 mV

Correct Answer: Greater than ±30 mV

Q8. Specific ion adsorption refers to:

• Ions only present in the bulk solution
• Ions binding chemically or strongly to the particle surface independent of electrostatic screening
• Ions that never interact with colloidal surfaces
• The liberation of counterions into bulk solvent

Correct Answer: Ions binding chemically or strongly to the particle surface independent of electrostatic screening

Q9. Which electrolyte will typically cause the fastest coagulation of a negatively charged latex: NaCl, CaCl2, or AlCl3?

• NaCl
• CaCl2
• AlCl3
• All equally

Correct Answer: AlCl3

Q10. What is the primary difference between coagulation and flocculation?

• Coagulation is reversible, flocculation is irreversible
• Coagulation neutralizes charge; flocculation promotes loose aggregate formation often via bridging
• Coagulation uses polymers; flocculation uses only salts
• There is no difference; terms are interchangeable

Correct Answer: Coagulation neutralizes charge; flocculation promotes loose aggregate formation often via bridging

Q11. Which factor most directly reduces the energy barrier against particle aggregation in DLVO theory?

• Increase in solvent viscosity
• Increase in ionic strength
• Decrease in particle density
• Increase in temperature only

Correct Answer: Increase in ionic strength

Q12. In the Stern model, the layer of ions tightly bound to the surface is called:

• Diffuse layer
• Stern layer (or compact layer)
• Hydration shell
• Van der Waals shell

Correct Answer: Stern layer (or compact layer)

Q13. Which mechanism describes stabilization by adsorbed polymers creating a physical barrier to aggregation?

• Electrostatic stabilization
• Steric stabilization
• Bridging coagulation
• Schulze–Hardy stabilization

Correct Answer: Steric stabilization

Q14. Bridging flocculation is typically caused by:

• Low molecular weight salts
• High molecular weight polymers adsorbing onto multiple particles
• Nonadsorbing small ions
• Surfactants at CMC only

Correct Answer: High molecular weight polymers adsorbing onto multiple particles

Q15. Which measurement technique is commonly used to determine zeta potential?

• Nuclear magnetic resonance (NMR)
• Electrophoretic light scattering (ELS)
• Infrared spectroscopy (IR)
• Mass spectrometry (MS)

Correct Answer: Electrophoretic light scattering (ELS)

Q16. How does pH influence electrolyte effects on colloids?

• pH only affects organic solvents, not colloids
• pH changes surface ionization and thus alters zeta potential and electrolyte sensitivity
• pH always neutralizes electrolytes
• pH increases van der Waals forces directly

Correct Answer: pH changes surface ionization and thus alters zeta potential and electrolyte sensitivity

Q17. Which statement about multivalent ions is correct in colloidal systems?

• Multivalent ions are less effective than monovalent ions at neutralizing surface charge
• Multivalent ions can cause charge neutralization and bridging, promoting aggregation
• Multivalent ions always increase particle repulsion
• Multivalent ions do not interact with charged surfaces

Correct Answer: Multivalent ions can cause charge neutralization and bridging, promoting aggregation

Q18. An increase in electrolyte concentration typically causes which change in electrophoretic mobility of particles?

• Mobility increases indefinitely
• Mobility decreases due to reduction in zeta potential and double layer thickness
• Mobility becomes independent of surface charge
• Mobility inverts sign without other effects

Correct Answer: Mobility decreases due to reduction in zeta potential and double layer thickness

Q19. Which of the following best explains “charge reversal” or overcharging of colloids?

• Excess adsorption of counterions leads to net surface charge of opposite sign
• Removal of all ions from solution
• Thermal decomposition of colloid surface
• Formation of covalent bonds between particles

Correct Answer: Excess adsorption of counterions leads to net surface charge of opposite sign

Q20. In pharmaceutical suspensions, control of electrolytes is important because:

• Electrolytes never affect drug bioavailability
• They can alter suspension stability, particle aggregation, and dosing uniformity
• Only flavor is impacted by electrolytes
• Electrolytes only affect color, not stability

Correct Answer: They can alter suspension stability, particle aggregation, and dosing uniformity

Q21. Which of the following ions is an example of a chaotropic ion affecting protein colloids (Hofmeister series concept)?

• Sulfate (SO4^2−)
• Perchlorate (ClO4−)
• Fluoride (F−)
• Carbonate (CO3^2−)

Correct Answer: Perchlorate (ClO4−)

Q22. For a negatively charged colloid, which anion would most likely decrease colloidal stability by specific adsorption?

• Perchlorate
• Hydroxide
• Nitrate
• None; anions never adsorb

Correct Answer: Perchlorate

Q23. Which role can chelating agents (e.g., EDTA) play in colloid stability?

• Promote coagulation by adding multivalent cations
• Sequester multivalent cations, preventing bridging and improving stability
• Increase ionic strength dramatically
• Convert colloids into covalent solids

Correct Answer: Sequester multivalent cations, preventing bridging and improving stability

Q24. What happens to van der Waals attraction when electrolyte concentration is increased?

• Van der Waals attraction increases dramatically with ionic strength
• Van der Waals attraction is largely unaffected by electrolytes
• Van der Waals attraction becomes repulsive
• Van der Waals attraction disappears

Correct Answer: Van der Waals attraction is largely unaffected by electrolytes

Q25. Which practical method is used to determine the CCC experimentally?

• Measuring change in color only
• Monitoring turbidity or absorbance as electrolyte concentration is increased
• Measuring pH at constant ionic strength only
• Observing smell changes in suspension

Correct Answer: Monitoring turbidity or absorbance as electrolyte concentration is increased

Q26. Lyophilic colloids compared to lyophobic colloids generally show:

• Greater sensitivity to small amounts of electrolytes
• Less sensitivity to electrolytes and more solvation by solvent molecules
• The same behavior toward electrolytes
• Immediate precipitation in any electrolyte

Correct Answer: Less sensitivity to electrolytes and more solvation by solvent molecules

Q27. Which statement best describes the effect of divalent cations on negatively charged polymer-coated particles?

• Divalent cations have no effect on polymers
• Divalent cations may form ionic bridges between polymer chains causing aggregation
• Divalent cations always stabilize polymer-coated particles sterically
• Divalent cations convert polymers to surfactants

Correct Answer: Divalent cations may form ionic bridges between polymer chains causing aggregation

Q28. Which is a direct consequence of double layer compression by electrolytes?

• Increase in repulsive energy barrier
• Decrease in repulsive energy barrier leading to aggregation
• Complete elimination of van der Waals forces
• Increase in particle solubility

Correct Answer: Decrease in repulsive energy barrier leading to aggregation

Q29. In designing a stable parenteral suspension, which electrolyte strategy is preferable?

• Use high concentration of multivalent salts to prevent aggregation
• Control ionic strength, avoid excess multivalent ions, and use steric stabilizers as needed
• Ensure zero ionic strength at all times
• Use only strong acids as electrolytes

Correct Answer: Control ionic strength, avoid excess multivalent ions, and use steric stabilizers as needed

Q30. Which phenomenon explains why particles may sediment faster after electrolyte addition?

• Increased Brownian motion
• Aggregation increases effective particle size and sedimentation rate
• Electrolytes reduce gravitational acceleration
• Electrolytes decrease particle density

Correct Answer: Aggregation increases effective particle size and sedimentation rate

Q31. A colloid shows rapid coagulation when 0.001 M of AlCl3 is added but needs 0.1 M NaCl for similar effect. This exemplifies:

• Hofmeister series
• Schulze–Hardy rule
• Gibbs adsorption isotherm
• Van ‘t Hoff law

Correct Answer: Schulze–Hardy rule

Q32. What is the expected sign of zeta potential for a silica particle in neutral water? (general case)

• Strongly positive
• Approximately neutral
• Negative due to deprotonated silanol groups
• Always zero

Correct Answer: Negative due to deprotonated silanol groups

Q33. If anionic surfactant and NaCl are both present, how can NaCl influence micelle/colloid behavior?

• NaCl increases electrostatic repulsion between anionic headgroups
• NaCl screens headgroup charge, reducing repulsion and possibly promoting aggregation or lowering CMC
• NaCl converts surfactant to cationic form
• NaCl has no effect on surfactant systems

Correct Answer: NaCl screens headgroup charge, reducing repulsion and possibly promoting aggregation or lowering CMC

Q34. Which of the following best describes “bridging” in polymer-induced flocculation?

• Polymer adsorbs to one particle only
• Polymer adsorbs onto multiple particles forming links between them
• Polymers reduce particle size by cleavage
• Polymers increase electrostatic repulsion exclusively

Correct Answer: Polymer adsorbs onto multiple particles forming links between them

Q35. How does temperature typically affect electrolyte-induced coagulation rates?

• Temperature has no influence
• Higher temperature generally increases kinetic energy and can increase aggregation rates, but effects are system dependent
• Higher temperature always decreases aggregation rates
• Temperature converts electrolytes into nonionic molecules

Correct Answer: Higher temperature generally increases kinetic energy and can increase aggregation rates, but effects are system dependent

Q36. Which is a common laboratory sign that a suspension has coagulated after electrolyte addition?

• Increase in turbidity followed by rapid clarification and sediment formation
• Permanent increase in pH only
• Change in color to blue
• Immediate gas evolution

Correct Answer: Increase in turbidity followed by rapid clarification and sediment formation

Q37. Which particle property is directly altered when specific ions adsorb onto the surface?

• Particle crystalline structure
• Surface charge density and chemical potential at the interface
• Atomic number of elements in particle
• Magnetic susceptibility only

Correct Answer: Surface charge density and chemical potential at the interface

Q38. Which of these is a likely effect of adding NaCl to a protein colloid near its isoelectric point?

• Proteins become more soluble indefinitely
• Salt may promote aggregation by screening charges and reducing repulsion
• Salt chemically denatures proteins in all cases
• Salt always prevents aggregation regardless of concentration

Correct Answer: Salt may promote aggregation by screening charges and reducing repulsion

Q39. The Debye length is inversely related to which of the following?

• Square root of ionic strength
• Square of particle diameter
• Viscosity of solvent
• Dielectric constant directly

Correct Answer: Square root of ionic strength

Q40. Which principle helps explain why trace multivalent impurities dramatically affect colloidal stability?

• Van ‘t Hoff principle
• Schulze–Hardy rule indicating strong effect of counterion valency
• Le Chatelier’s principle
• Henderson–Hasselbalch equation

Correct Answer: Schulze–Hardy rule indicating strong effect of counterion valency

Q41. In formulation work, adding small amounts of electrolyte sometimes improves stability by:

• Completely neutralizing all charges
• Screening repulsions to an optimum and enabling formation of a uniform, loosely flocculated network that resists caking
• Increasing particle solubility only
• Turning colloids into solutions

Correct Answer: Screening repulsions to an optimum and enabling formation of a uniform, loosely flocculated network that resists caking

Q42. Which of the following is NOT a way electrolytes can affect colloids?

• Compress the double layer
• Change surface potential via adsorption
• Alter van der Waals forces significantly
• Promote bridging with multivalent ions

Correct Answer: Alter van der Waals forces significantly

Q43. How would you expect NaCl vs CaCl2 to differ in causing aggregation of negatively charged particles at equal molar concentrations?

• NaCl causes stronger aggregation than CaCl2
• CaCl2 causes stronger aggregation than NaCl due to Ca2+ valency
• Both have identical effect at equal molarities
• Neither causes aggregation

Correct Answer: CaCl2 causes stronger aggregation than NaCl due to Ca2+ valency

Q44. What is the likely effect of adding an anionic surfactant to a negatively charged particle suspension?

• Increase in particle charge magnitude and enhanced electrostatic repulsion
• Immediate neutralization of particles
• Formation of covalent bonds
• Conversion to crystalline solids

Correct Answer: Increase in particle charge magnitude and enhanced electrostatic repulsion

Q45. For a charged colloid, which parameter would you monitor to assess electrolyte-induced destabilization quantitatively?

• Zeta potential and turbidity over incremental electrolyte additions
• Only particle color
• Only solvent boiling point
• Only chemical formula of solute

Correct Answer: Zeta potential and turbidity over incremental electrolyte additions

Q46. Which describes an ion-specific (non-DLVO) effect on colloids?

• Purely electrostatic screening explained by ionic strength
• Specific adsorption altering surface chemistry beyond simple screening
• Only van der Waals interactions
• None; all effects are DLVO

Correct Answer: Specific adsorption altering surface chemistry beyond simple screening

Q47. What is the expected effect of increasing salt concentration on emulsion droplet stability when droplets are stabilized purely by electrostatic repulsion?

• Stability increases as salt concentration increases
• Stability decreases because electrostatic repulsion is screened
• Salt converts emulsion to solution
• Salt always generates new surfactant molecules

Correct Answer: Stability decreases because electrostatic repulsion is screened

Q48. Which approach can be used to counteract electrolyte-induced destabilization in pharmaceutical suspensions?

• Remove steric stabilizers and increase salt
• Add polymeric steric stabilizers or adjust pH to increase surface charge magnitude
• Add more multivalent cations
• Increase ionic strength further

Correct Answer: Add polymeric steric stabilizers or adjust pH to increase surface charge magnitude

Q49. The term “double layer compression” quantitatively corresponds to a decrease in which of the following?

• Van der Waals force magnitude
• Debye length
• Particle core radius
• Dielectric constant of water

Correct Answer: Debye length

Q50. When preparing exam-style calculations for CCC, which trend would you expect when counterion valency increases?

• CCC increases with higher valency
• CCC decreases sharply with higher valency
• CCC remains unchanged
• CCC depends only on particle size, not valency

Correct Answer: CCC decreases sharply with higher valency

G S Sachin

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