Measurement of tonicity MCQs With Answer

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Measurement of Tonicity MCQs with Answers helps B. Pharm students master pharmaceutics concepts essential for safe ophthalmic and parenteral formulation design. This topic covers isotonicity, osmolarity vs osmolality, freezing point depression (cryoscopic) method, sodium chloride equivalent (E-value) method, White–Vincent method, and Sprowls method, plus clinical impacts like hemolysis, crenation, and patient comfort. You’ll learn constants (e.g., ΔTf for isotonic solutions ≈ 0.52°C), calculation steps, and how effective osmoles determine tonicity across membranes. Mastering tonicity measurement ensures accurate tonicity adjustment with NaCl, dextrose, mannitol, or isotonic buffers in real-world compounding. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which best defines tonicity in pharmaceutics?

  • The effective osmotic pressure exerted by nonpermeant solutes across a semipermeable membrane
  • The total osmolality of a solution regardless of membrane permeability
  • The solution’s vapor pressure relative to pure water
  • The hydrogen ion activity determining solution pH

Correct Answer: The effective osmotic pressure exerted by nonpermeant solutes across a semipermeable membrane

Q2. The cryoscopic method of tonicity measurement relies primarily on which principle?

  • Equal freezing point depressions correspond to equal tonicity
  • Equal boiling points correspond to equal tonicity
  • Equal pH values ensure isotonicity
  • Equal viscosities correspond to equal tonicity

Correct Answer: Equal freezing point depressions correspond to equal tonicity

Q3. The freezing point depression of body fluids and isotonic NaCl solutions is approximately:

  • 0.18°C
  • 0.52°C
  • 1.86°C
  • 3.43°C

Correct Answer: 0.52°C

Q4. A 1% w/v NaCl solution has a ΔTf of about 0.576°C. Which NaCl strength is closest to isotonic with body fluids?

  • 0.58% w/v
  • 0.90% w/v
  • 1.10% w/v
  • 1.80% w/v

Correct Answer: 0.90% w/v

Q5. Osmolarity and osmolality differ because:

  • Osmolarity is per liter of solution, osmolality is per kilogram of solvent
  • Osmolarity is per kilogram of solvent, osmolality is per liter of solution
  • Osmolarity ignores electrolytes; osmolality counts ions
  • They are identical terms

Correct Answer: Osmolarity is per liter of solution, osmolality is per kilogram of solvent

Q6. Hypotonic solutions relative to RBCs typically cause:

  • Crenation
  • Hemolysis
  • Precipitation
  • Increased buffer capacity

Correct Answer: Hemolysis

Q7. Hypertonic solutions relative to RBCs typically cause:

  • Crenation
  • Hemolysis
  • Polymerization
  • Neutralization

Correct Answer: Crenation

Q8. Which solute produces an isosmotic but hypotonic solution for RBCs due to high permeability?

  • Sodium chloride
  • Dextrose
  • Mannitol
  • Urea

Correct Answer: Urea

Q9. Which method directly uses the sodium chloride equivalent (E-value) to adjust tonicity?

  • E-value (sodium chloride equivalent) method
  • Cryoscopic method
  • pH adjustment method
  • Partition coefficient method

Correct Answer: E-value (sodium chloride equivalent) method

Q10. In the E-value method, the first step to make 100 mL isotonic is to compute:

  • Grams of NaCl needed for isotonicity (0.9 g/100 mL)
  • Grams of buffer salts required
  • Volume of isotonic diluting solution needed
  • mEq of sodium required per dose

Correct Answer: Grams of NaCl needed for isotonicity (0.9 g/100 mL)

Q11. The White–Vincent method is best described as a:

  • Volume adjustment method that calculates V = w × E × 111.1 mL, then brings to final volume with an isotonic diluent
  • Weight adjustment method that adds NaCl directly to make isotonic
  • pH neutralization method using buffers
  • Sterility assurance method for ophthalmics

Correct Answer: Volume adjustment method that calculates V = w × E × 111.1 mL, then brings to final volume with an isotonic diluent

Q12. The Sprowls method primarily involves:

  • Using pre-tabulated V-values to quickly determine the volume of isotonic solution per gram of drug
  • Measuring vapor pressure to infer tonicity
  • Neutralizing the formulation to pH 7.4
  • Adding excess NaCl then back-diluting

Correct Answer: Using pre-tabulated V-values to quickly determine the volume of isotonic solution per gram of drug

Q13. Typical osmolality of human plasma is closest to:

  • 150–200 mOsm/kg
  • 250–260 mOsm/kg
  • 285–295 mOsm/kg
  • 330–350 mOsm/kg

Correct Answer: 285–295 mOsm/kg

Q14. Which colligative property is most widely used to assess isotonicity?

  • Freezing point depression
  • Boiling point elevation
  • Vapor pressure lowering
  • Surface tension

Correct Answer: Freezing point depression

Q15. Regarding tonicity versus osmolarity, which is correct?

  • Tonicity depends on membrane permeability; osmolarity does not
  • Osmolarity depends on permeability; tonicity does not
  • Both depend on permeability equally
  • Neither depends on permeability

Correct Answer: Tonicity depends on membrane permeability; osmolarity does not

Q16. Ophthalmic solutions are adjusted to isotonicity primarily to:

  • Minimize irritation and reflex lacrimation
  • Increase viscosity
  • Improve color stability
  • Enhance lipid solubility

Correct Answer: Minimize irritation and reflex lacrimation

Q17. The reflection coefficient (σ) in tonicity describes:

  • The membrane’s effectiveness in preventing solute passage (σ≈1 for impermeant solutes)
  • The buffer capacity near pH 7
  • The osmometer calibration constant
  • The viscosity ratio of solution to water

Correct Answer: The membrane’s effectiveness in preventing solute passage (σ≈1 for impermeant solutes)

Q18. The approximate osmolarity of 0.9% w/v NaCl (MW 58.5) is:

  • 154 mOsm/L
  • 270 mOsm/L
  • 308 mOsm/L
  • 450 mOsm/L

Correct Answer: 308 mOsm/L

Q19. Which is true about 5% dextrose in water (D5W)?

  • It is isosmotic in the bag but may become hypotonic in vivo as dextrose is metabolized
  • It is hypertonic and remains hypertonic in vivo
  • It is hypotonic in the bag and in vivo
  • It is isotonic and remains unchanged metabolically

Correct Answer: It is isosmotic in the bag but may become hypotonic in vivo as dextrose is metabolized

Q20. A commonly used non-ionic tonicity adjuster in formulations is:

  • Mannitol
  • Potassium chloride
  • Calcium chloride
  • Acetic acid

Correct Answer: Mannitol

Q21. To make 100 mL of an isotonic solution with NaCl, the grams of NaCl required are:

  • 0.09 g
  • 0.90 g
  • 1.80 g
  • 9.00 g

Correct Answer: 0.90 g

Q22. Using the E-value method: For 30 mL solution, NaCl needed is 0.27 g. If 0.5 g of drug has E = 0.18, how much NaCl should be added?

  • 0.09 g
  • 0.18 g
  • 0.27 g
  • 0.36 g

Correct Answer: 0.18 g

Q23. Acceptable tonicity range for comfort in ophthalmic solutions (as NaCl equivalent) is approximately:

  • 0.2%–0.5% w/v NaCl
  • 0.6%–2.0% w/v NaCl
  • 2%–5% w/v NaCl
  • 10%–15% w/v NaCl

Correct Answer: 0.6%–2.0% w/v NaCl

Q24. The statement best describing isotonic buffers in ophthalmics is:

  • They maintain both pH and tonicity when used as the diluent
  • They only adjust viscosity
  • They eliminate the need for preservatives
  • They guarantee sterility without filtration

Correct Answer: They maintain both pH and tonicity when used as the diluent

Q25. Regarding infusion safety, solutions above which osmolality typically require central venous administration?

  • >150 mOsm/L
  • >300 mOsm/L
  • >600 mOsm/L
  • >900 mOsm/L

Correct Answer: >900 mOsm/L

Q26. Which statement about boric acid in ophthalmics is correct?

  • ~1.9% w/v boric acid can be isotonic with tears but is not isotonic with blood
  • ~1.9% w/v boric acid is isotonic with both tears and blood
  • Boric acid cannot be used to adjust tonicity
  • Boric acid is preferred IV osmotic agent

Correct Answer: ~1.9% w/v boric acid can be isotonic with tears but is not isotonic with blood

Q27. Classify the methods: Which is a Class II (volume) method?

  • White–Vincent method
  • E-value (NaCl equivalent) method
  • Direct addition of NaCl method
  • Electrolyte balancing method

Correct Answer: White–Vincent method

Q28. Which instrument most directly measures osmolality via freezing point?

  • Freezing point osmometer
  • pH meter
  • Refractometer
  • Viscometer

Correct Answer: Freezing point osmometer

Q29. Which colligative property is least relevant for tonicity adjustment in practice?

  • Freezing point depression
  • Boiling point elevation
  • Vapor pressure lowering
  • Refractive index

Correct Answer: Refractive index

Q30. Using E-values: For 100 mL, a 2% w/v drug (2 g) has E = 0.30. How much NaCl should be added?

  • 0.30 g
  • 0.60 g
  • 0.90 g
  • 1.20 g

Correct Answer: 0.30 g

Q31. Which statement about isosmotic vs isotonic is correct?

  • Isosmotic solutions have equal total solute particles; isotonic solutions account for solute permeability
  • Isotonic solutions have equal total solute particles; isosmotic accounts for permeability
  • They are always identical concepts
  • Isosmotic applies only to colloids

Correct Answer: Isosmotic solutions have equal total solute particles; isotonic solutions account for solute permeability

Q32. Why might RBC-based tonicity tests not fully predict ocular comfort?

  • Corneal epithelium has different permeability and buffering than RBC membranes
  • RBC tests ignore viscosity
  • RBC tests require sterile technique
  • RBCs lack proteins

Correct Answer: Corneal epithelium has different permeability and buffering than RBC membranes

Q33. Mannitol 20% is used clinically because it:

  • Creates a hypertonic gradient to draw water from tissues
  • Neutralizes acids in blood
  • Is isotonic with CSF
  • Lowers viscosity of plasma

Correct Answer: Creates a hypertonic gradient to draw water from tissues

Q34. The freezing point of lacrimal fluid is approximately:

  • -0.18°C
  • -0.52°C
  • -1.00°C
  • -1.86°C

Correct Answer: -0.52°C

Q35. In an isotonic medium, RBCs maintain their typical morphology, which is:

  • Biconcave discs
  • Spherical cells
  • Spiculated cells
  • Lysed ghosts

Correct Answer: Biconcave discs

Q36. The preferred practical method to adjust ophthalmic isotonicity when E-values are known is:

  • E-value (sodium chloride equivalent) method
  • Refractometric adjustment
  • Sterilization by filtration
  • Lyophilization

Correct Answer: E-value (sodium chloride equivalent) method

Q37. For hypertonic formulations that must be made isotonic, the most appropriate general approach is:

  • Dilute with water and then q.s. with an isotonic diluting solution (Class II method)
  • Add more NaCl to stabilize
  • Lower pH to 3.0
  • Add surfactants

Correct Answer: Dilute with water and then q.s. with an isotonic diluting solution (Class II method)

Q38. Which solutes determine tonicity across a biological membrane?

  • Solutes with low permeability (effective osmoles)
  • All solutes regardless of permeability
  • Only electrolytes
  • Only nonelectrolytes

Correct Answer: Solutes with low permeability (effective osmoles)

Q39. If E-calculations show the drug contributes more than 0.9 g NaCl equivalent per 100 mL (apparent hypertonicity), you should:

  • Dilute with water and complete to volume with an isotonic vehicle rather than adding NaCl
  • Add negative NaCl
  • Increase buffer concentration
  • Add a permeant solute like urea

Correct Answer: Dilute with water and complete to volume with an isotonic vehicle rather than adding NaCl

Q40. Usual acceptable osmolality range for IV solutions to be considered near-isotonic is:

  • 100–150 mOsm/kg
  • 200–240 mOsm/kg
  • 270–310 mOsm/kg
  • 400–500 mOsm/kg

Correct Answer: 270–310 mOsm/kg

Q41. The cryoscopic method adjusts tonicity by equating:

  • ΔTf of the preparation to 0.52°C
  • pH to 7.4
  • Viscosity to that of tears
  • Surface tension to that of water

Correct Answer: ΔTf of the preparation to 0.52°C

Q42. Term for RBC shrinkage in hypertonic solutions is:

  • Crenation
  • Hemolysis
  • Agglutination
  • Coalescence

Correct Answer: Crenation

Q43. Adding dextrose to a formulation primarily affects:

  • Tonicity/osmolality without adding electrolytes
  • pH neutralization to 7
  • Protein binding
  • Surface activity

Correct Answer: Tonicity/osmolality without adding electrolytes

Q44. For 50 mL ophthalmic solution: drug amount = 0.4 g, E = 0.14. How much NaCl should be added?

  • 0.34 g
  • 0.39 g
  • 0.45 g
  • 0.50 g

Correct Answer: 0.39 g

Q45. Which is the correct sequence for the White–Vincent method?

  • Calculate V = w × E × 111.1 mL; add water to make V; then add isotonic diluent to final volume
  • Add NaCl directly to the final volume
  • Neutralize to pH 7 first
  • Measure osmolality and ignore permeability

Correct Answer: Calculate V = w × E × 111.1 mL; add water to make V; then add isotonic diluent to final volume

Q46. Which component can serve as a tonicity agent in ophthalmic products besides NaCl?

  • Boric acid
  • Silver nitrate
  • Sodium hydroxide
  • Benzalkonium chloride

Correct Answer: Boric acid

Q47. The standard unit for reporting osmolality in compounding is:

  • mOsmol/L
  • mOsmol/kg
  • mmol/L
  • % w/v

Correct Answer: mOsmol/kg

Q48. Which combination is approximately isotonic with tears?

  • 0.9% w/v NaCl and about 1.9% w/v boric acid
  • 5% w/v dextrose and 0.45% w/v NaCl
  • 3% w/v NaCl and 0.9% w/v boric acid
  • 0.45% w/v NaCl and 10% w/v mannitol

Correct Answer: 0.9% w/v NaCl and about 1.9% w/v boric acid

Q49. Which permeant solute contributes poorly to tonicity across RBC membranes?

  • Urea
  • Mannitol
  • Sodium chloride
  • Sucrose

Correct Answer: Urea

Q50. The approximate osmolarity of 5% w/v dextrose (MW 180) is:

  • 154 mOsm/L
  • 278 mOsm/L
  • 308 mOsm/L
  • 500 mOsm/L

Correct Answer: 278 mOsm/L

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