Solubility of gases in liquids MCQs With Answer is a focused review for B. Pharm students covering principles that determine gas solubility in pharmaceutical systems. This introduction highlights Henry’s law, temperature and pressure effects, gas–liquid partitioning, Ostwald and Bunsen coefficients, and enthalpy of dissolution. Understanding how salting-out, solvent polarity, surfactants and formulation variables influence gas uptake helps in drug formulation, sterilization, carbonated products and anesthetic delivery. Practical topics include blood–gas partition coefficients, headspace analysis, and methods to measure and predict gas solubility. Clear conceptual mastery is essential for exams and lab work. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. Which statement best describes Henry’s law for dilute solutions?
- The partial pressure of a gas above a liquid is proportional to the mole fraction of the gas in the liquid.
- The solubility of a gas is independent of its partial pressure.
- The solubility of a gas is inversely proportional to temperature.
- The partial pressure of a gas equals its concentration multiplied by the gas constant.
Correct Answer: The partial pressure of a gas above a liquid is proportional to the mole fraction of the gas in the liquid.
Q2. How does increasing temperature generally affect the solubility of most gases in liquids?
- Solubility increases with temperature.
- Solubility decreases with temperature.
- Solubility is unaffected by temperature.
- Solubility first increases then decreases with temperature.
Correct Answer: Solubility decreases with temperature.
Q3. Which coefficient describes the volume of gas dissolved per unit volume of solvent at standard temperature and pressure per unit partial pressure?
- Ostwald coefficient
- Bunsen coefficient
- Partition coefficient
- Henry’s constant
Correct Answer: Bunsen coefficient
Q4. The Ostwald solubility coefficient is defined as:
- The ratio of moles of gas in solvent to moles in gas phase at equilibrium under same conditions.
- The volume of gas at STP per volume of solvent per atmosphere.
- The ratio of gas partial pressure to mole fraction in solvent.
- The Henry’s law constant expressed in Pa·m3/mol.
Correct Answer: The ratio of moles of gas in solvent to moles in gas phase at equilibrium under same conditions.
Q5. Which gas is generally most soluble in water at 25 °C?
- Nitrogen (N2)
- Oxygen (O2)
- Carbon dioxide (CO2)
- Helium (He)
Correct Answer: Carbon dioxide (CO2)
Q6. Which factor does NOT significantly affect gas solubility in pharmaceutical liquids?
- Temperature
- Pressure
- Solvent polarity
- Color of container
Correct Answer: Color of container
Q7. Henry’s law constant (kH) relates which two quantities?
- Partial pressure of the gas and mole fraction in the liquid
- Temperature and enthalpy change
- Viscosity and diffusion coefficient
- Surface tension and vapor pressure
Correct Answer: Partial pressure of the gas and mole fraction in the liquid
Q8. In pharmaceutical headspace analysis, higher gas solubility in the matrix will generally result in:
- Higher headspace concentration of gas
- Lower headspace concentration of gas
- No change in headspace concentration
- Complete disappearance of gas
Correct Answer: Lower headspace concentration of gas
Q9. The salting-out effect causes gas solubility to:
- Increase when salts are added
- Decrease when salts are added
- Remain unchanged with salt addition
- Oscillate with salt concentration
Correct Answer: Decrease when salts are added
Q10. Which expression describes the temperature dependence of Henry’s constant using enthalpy of dissolution?
- van ‘t Hoff equation
- Arrhenius equation
- Clausius-Clapeyron equation
- Stokes-Einstein relation
Correct Answer: van ‘t Hoff equation
Q11. For gas dissolution that is exothermic, increasing temperature will:
- Increase gas solubility
- Decrease gas solubility
- Have no effect
- Completely dissociate the gas
Correct Answer: Decrease gas solubility
Q12. Which method is commonly used to determine gas solubility in the lab for pharmaceutical samples?
- Headspace gas chromatography
- Thin-layer chromatography
- Gel permeation chromatography
- Infrared spectrophotometry of solid
Correct Answer: Headspace gas chromatography
Q13. Blood–gas partition coefficient is important for which pharmaceutical application?
- Oral tablet dissolution testing
- Anesthetic uptake and onset
- Topical cream absorption
- Lyophilization process
Correct Answer: Anesthetic uptake and onset
Q14. Which gas shows strong chemical interaction with water increasing apparent solubility via reaction?
- Helium
- Carbon dioxide
- Neon
- Nitrogen
Correct Answer: Carbon dioxide
Q15. When Henry’s law fails to predict gas solubility accurately?
- At very low concentrations
- For ideal dilute systems
- When chemical reactions or strong association occur
- When temperature is constant
Correct Answer: When chemical reactions or strong association occur
Q16. Which of the following increases the solubility of oxygen in a formulation?
- Raising temperature
- Increasing partial pressure of oxygen over the liquid
- Adding salts that cause salting-out
- Reducing solvent polarity drastically
Correct Answer: Increasing partial pressure of oxygen over the liquid
Q17. The dimensionless Henry’s constant (Hcc) is defined as:
- Concentration in gas phase divided by concentration in liquid phase
- Partial pressure divided by mole fraction
- Ratio of gas concentration in liquid to concentration in gas at equilibrium
- Volume of gas per mass of solvent
Correct Answer: Ratio of gas concentration in liquid to concentration in gas at equilibrium
Q18. Which solvent property generally increases gas solubility?
- High polarity for nonpolar gas
- High viscosity always
- Good chemical affinity between gas and solvent
- High surface tension
Correct Answer: Good chemical affinity between gas and solvent
Q19. Salting-in refers to:
- Decrease in gas solubility on salt addition
- Increase in gas solubility on salt addition
- No change in solubility with salt
- Gas escaping from solution
Correct Answer: Increase in gas solubility on salt addition
Q20. In formulations, reducing dissolved oxygen is critical because oxygen can:
- Promote oxidative degradation of drugs
- Sterilize the product
- Stabilize peroxides
- Increase pH dramatically
Correct Answer: Promote oxidative degradation of drugs
Q21. Which statement about the Bunsen coefficient (α) is correct?
- It is the ratio of gas concentration in solution to concentration in gas at same temperature and pressure.
- It expresses volume of gas at STP dissolved per unit volume of solvent per atm.
- It is dimensionless and identical to Henry’s constant.
- It measures the diffusion rate of gas in liquid.
Correct Answer: It expresses volume of gas at STP dissolved per unit volume of solvent per atm.
Q22. Which experimental condition will decrease gas solubility in a vial during sterilization?
- Cooling the vial
- Pressurizing the headspace with inert gas
- Heating the vial
- Adding an antioxidant
Correct Answer: Heating the vial
Q23. Henry’s law constant kH for a gas usually:
- Decreases as temperature increases for most gases
- Increases as temperature increases for most gases
- Remains constant with temperature change
- Is independent of solvent
Correct Answer: Increases as temperature increases for most gases
Q24. Reactive absorption of CO2 in a basic solution will cause observed solubility to be:
- Lower than predicted by Henry’s law
- Higher than predicted by Henry’s law
- Exactly as predicted by Henry’s law
- Independent of pH
Correct Answer: Higher than predicted by Henry’s law
Q25. Which gas has the lowest solubility in water at 25 °C among common atmospheric gases?
- Oxygen (O2)
- Nitrogen (N2)
- Carbon dioxide (CO2)
- Argon (Ar)
Correct Answer: Nitrogen (N2)
Q26. Which formulation strategy can reduce dissolved oxygen in a liquid pharmaceutical product?
- Degassing by sonication or vacuum
- Increasing storage temperature
- Adding soluble salts to salt-in
- Shaking vigorously before sealing
Correct Answer: Degassing by sonication or vacuum
Q27. In the context of inhalational anesthetics, a higher blood–gas partition coefficient indicates:
- Faster induction and recovery
- Slower induction and recovery
- No effect on induction
- Lower potency
Correct Answer: Slower induction and recovery
Q28. Which term best describes when gas solubility is controlled by its partial pressure over the liquid?
- Raoult’s regime
- Henry’s regime
- Ostwald equilibrium
- Stokes regime
Correct Answer: Henry’s regime
Q29. Which of the following increases CO2 solubility significantly compared to O2 in water?
- CO2 forms carbonic acid and other species in water
- CO2 is less dense than O2
- CO2 is nonpolar
- CO2 has lower molecular weight
Correct Answer: CO2 forms carbonic acid and other species in water
Q30. Which analytical parameter is directly affected by gas solubility when using headspace GC for volatile impurities?
- Distribution ratio between headspace and matrix
- Viscosity of mobile phase
- Chromatographic column length
- pH of detector
Correct Answer: Distribution ratio between headspace and matrix
Q31. The enthalpy of dissolution for most gas solvation in water is:
- Highly endothermic
- Typically exothermic
- Always zero
- Undefined
Correct Answer: Typically exothermic
Q32. Which is a common unit for Henry’s law constant when expressed as p = kH·x?
- mol·L−1
- atm
- atm·(mole fraction)−1
- J·mol−1·K−1
Correct Answer: atm·(mole fraction)−1
Q33. In gas–liquid systems, which additive commonly increases gas solubility by forming micelles?
- Nonionic surfactant
- Strong oxidizing agent
- Hydrophobic dye
- Insoluble polymer
Correct Answer: Nonionic surfactant
Q34. Which physical process speeds equilibration of gas between liquid and headspace?
- Reducing surface area
- Stirring or agitation
- Increasing solution viscosity
- Cooling the system
Correct Answer: Stirring or agitation
Q35. For biological relevance, the oxygen solubility in blood is influenced primarily by:
- Hemoglobin binding and physical solubility
- Only physical solubility in plasma
- Only hemoglobin concentration, not solubility
- Surface tension of blood
Correct Answer: Hemoglobin binding and physical solubility
Q36. Which statement about Henry’s law and non-ideal solutions is true?
- Henry’s law always holds, even in concentrated solutions.
- Deviations occur when gas interacts chemically or solution is non-ideal.
- Henry’s law is only applicable to solids in liquids.
- Henry’s law predicts vapor pressure of volatile liquids.
Correct Answer: Deviations occur when gas interacts chemically or solution is non-ideal.
Q37. The practical importance of knowing gas solubility in formulations includes:
- Predicting color changes only
- Optimizing packaging to limit oxidation and ensure stability
- Calculating tablet hardness
- Determining melting point
Correct Answer: Optimizing packaging to limit oxidation and ensure stability
Q38. Which gas is most commonly used to inert headspace to reduce oxygen solubility?
- Carbon dioxide
- Nitrogen
- Oxygen
- Ammonia
Correct Answer: Nitrogen
Q39. In calculating dissolved gas concentration from Henry’s law, which input is essential?
- Partial pressure of the gas above the liquid
- Surface tension value
- Electrical conductivity of the liquid
- Molecular viscosity of gas
Correct Answer: Partial pressure of the gas above the liquid
Q40. Which process will increase headspace oxygen after vial sealing?
- Complete degassing before filling
- Permeation of oxygen through closure over time
- Use of oxygen-scavenging materials
- Filling under nitrogen atmosphere
Correct Answer: Permeation of oxygen through closure over time
Q41. Which is a sign that a gas is reacting in solution rather than obeying Henry’s law?
- Linear relationship between partial pressure and solubility
- Observed solubility much higher than predicted and time-dependent consumption
- No change with temperature
- Immediate attainment of equilibrium with no chemical change
Correct Answer: Observed solubility much higher than predicted and time-dependent consumption
Q42. Which mathematical relationship can estimate the change in Henry’s constant with temperature if enthalpy of dissolution is known?
- Integrated van ‘t Hoff equation
- Beer-Lambert law
- Raoult’s law
- Fick’s second law
Correct Answer: Integrated van ‘t Hoff equation
Q43. In carbonated beverages, CO2 solubility is increased by:
- Higher temperature
- Higher pressure during bottling
- Long storage at room temperature
- Adding alcohol
Correct Answer: Higher pressure during bottling
Q44. Which property correlates with the tendency of a gas to dissolve in organic solvents compared with water?
- Polarity and Henry’s law constant differences
- Only molecular weight
- Only color of gas
- Boiling point of solvent exclusively
Correct Answer: Polarity and Henry’s law constant differences
Q45. Which factor would most likely produce faster equilibration of anesthetic gas between alveolar air and blood?
- High blood–gas partition coefficient
- Low blood flow to lungs
- High alveolar ventilation
- Very low cardiac output
Correct Answer: High alveolar ventilation
Q46. The presence of organic co-solvents (e.g., ethanol) typically affects gas solubility by:
- Always decreasing solubility of all gases
- Altering solvent polarity and often increasing solubility of nonpolar gases
- Eliminating all dissolved gases
- Making Henry’s law invalid at any concentration
Correct Answer: Altering solvent polarity and often increasing solubility of nonpolar gases
Q47. Which parameter is directly useful for predicting oxygen transfer into a liquid during mixing?
- Oxygen mass transfer coefficient (kLa)
- Bunsen coefficient only
- Ostwald coefficient only
- pH of the solution exclusively
Correct Answer: Oxygen mass transfer coefficient (kLa)
Q48. In pharmaceutical packaging, choosing materials with low oxygen permeability helps because:
- It increases dissolved oxygen concentration
- It reduces ingress of oxygen and protects product from oxidation
- It raises headspace pressure over time
- It accelerates chemical reactions
Correct Answer: It reduces ingress of oxygen and protects product from oxidation
Q49. Which experimental change would increase measured gas solubility according to Henry’s law?
- Decrease gas partial pressure
- Increase gas partial pressure
- Raise temperature for most gases
- Add salting-out salts
Correct Answer: Increase gas partial pressure
Q50. Why is understanding gas solubility critical for B. Pharm students?
- It only matters for non-pharmaceutical industries
- It informs formulation stability, packaging, sterilization, and inhalation therapy design
- It replaces the need to study pharmacokinetics
- It is irrelevant for laboratory practice
Correct Answer: It informs formulation stability, packaging, sterilization, and inhalation therapy design
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