Ideal solutions MCQs With Answer

Ideal solutions MCQs With Answer provide B. Pharm students a focused way to master solution thermodynamics, Raoult’s law, colligative properties and activity concepts essential for pharmaceutical formulations. This collection emphasizes key terms like ideal solutions, vapor pressure lowering, boiling point elevation, freezing point depression, osmotic pressure, activity coefficient and partial molar properties to boost exam performance and practical understanding. Clear, targeted multiple-choice questions cover theory, calculations and real-world implications in drug formulation and analytical chemistry. Each question reinforces conceptual links between intermolecular forces, thermodynamic functions and lab measurements. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What defines an ideal solution?

• Solution with zero vapor pressure
• Solution where intermolecular interactions A–B differ greatly from A–A and B–B
• Solution that obeys Raoult’s law at all compositions and has ΔmixH = 0
• Solution that shows azeotropy

Correct Answer: Solution that obeys Raoult’s law at all compositions and has ΔmixH = 0

Q2. According to Raoult’s law, the partial vapor pressure of component A in an ideal solution is:

• pA = PA° + xA
• pA = xA · PA°
• pA = xB · PB°
• pA = PA° / xA

Correct Answer: pA = xA · PA°

Q3. Which thermodynamic change is zero for an ideal solution on mixing?

• ΔmixG
• ΔmixS
• ΔmixH
• ΔmixT

Correct Answer: ΔmixH

Q4. The activity of a solvent in an ideal solution equals:

• Its mole fraction
• Its molarity
• Its vapor pressure
• Its mass fraction

Correct Answer: Its mole fraction

Q5. Relative lowering of vapor pressure for a non-volatile solute is equal to:

• x_solvent
• x_solute
• Psolution / P°
• ΔHvap

Correct Answer: x_solute

Q6. Which property is considered colligative?

• Viscosity
• Boiling point elevation
• Color
• Optical rotation

Correct Answer: Boiling point elevation

Q7. For an ideal solution, the Gibbs-Duhem equation implies:

• Sum of chemical potentials equals zero
• Sum of xi dμi = 0
• dG = 0 for all processes
• Cp is constant

Correct Answer: Sum of xi dμi = 0

Q8. Positive deviation from Raoult’s law indicates:

• Stronger A–B interactions than A–A or B–B
• Weaker A–B interactions than A–A and B–B
• ΔmixH = 0
• Ideal mixing

Correct Answer: Weaker A–B interactions than A–A and B–B

Q9. Negative deviation from Raoult’s law typically leads to:

• Lower boiling point than ideal prediction
• Formation of minimum-boiling azeotrope
• Higher vapor pressure than predicted
• No change in colligative properties

Correct Answer: Formation of minimum-boiling azeotrope

Q10. In dilute ideal solutions, osmotic pressure (π) is given by:

• π = iMRT
• π = Kb · m
• π = ΔTf · Kf
• π = xsolute · P°

Correct Answer: π = iMRT

Q11. Freezing point depression (ΔTf) is proportional to:

• Molality of solute
• Mole fraction of solvent only
• Volume percent of solution
• Density difference

Correct Answer: Molality of solute

Q12. For an ideal binary liquid mixture of two volatile components, total vapor pressure Ptot equals:

• Ptot = PA° + PB°
• Ptot = xA · PA° + xB · PB°
• Ptot = xA / PA° + xB / PB°
• Ptot = PA° · PB°

Correct Answer: Ptot = xA · PA° + xB · PB°

Q13. Which statement about excess properties in an ideal solution is true?

• Excess Gibbs energy is positive
• Excess enthalpy is zero
• Excess volume is large and positive
• Excess entropy is negative

Correct Answer: Excess enthalpy is zero

Q14. Activity coefficient (γ) in an ideal solution equals:

• ∞
• 0
• 1
• Depends on temperature only

Correct Answer: 1

Q15. Which equation links chemical potential of component i in an ideal solution to its mole fraction?

• μi = μi° + RT ln xi
• μi = μi° + RT xi
• μi = μi° – RT / xi
• μi = μi° · xi

Correct Answer: μi = μi° + RT ln xi

Q16. Azeotropes are generally absent in:

• Strongly nonideal mixtures
• Ideal solutions
• Electrolyte solutions
• Polymeric solutions

Correct Answer: Ideal solutions

Q17. For a volatile solute at infinite dilution, which law is more appropriate?

• Raoult’s law for the solute
• Henry’s law for the solute
• Dalton’s law of partial pressures only
• Van’t Hoff law

Correct Answer: Henry’s law for the solute

Q18. The number of particles effect in colligative properties is described by:

• Molar mass only
• Van’t Hoff factor (i)
• Dielectric constant
• Surface tension

Correct Answer: Van’t Hoff factor (i)

Q19. Which of the following is true for ideal solutions regarding volume on mixing?

• Total volume equals sum of partial molar volumes unchanged (no volume change)
• Volume always decreases
• Volume always increases
• Volume behaves unpredictably

Correct Answer: Total volume equals sum of partial molar volumes unchanged (no volume change)

Q20. Relative lowering of vapor pressure is often used to determine:

• Boiling point of pure solvent
• Molar mass of solute
• Surface tension of solution
• Density of solute

Correct Answer: Molar mass of solute

Q21. In pharmaceutical formulations, why are ideal solution concepts useful?

• They exactly predict behavior for all mixtures
• They offer a first approximation to design and estimate colligative effects
• They replace the need for experimental data
• They are only used for gases

Correct Answer: They offer a first approximation to design and estimate colligative effects

Q22. Which quantity is zero for an ideal solution at a given temperature and pressure when components are mixed?

• ΔmixG
• ΔmixS
• ΔmixH
• Chemical potential of each component

Correct Answer: ΔmixH

Q23. For a dilute solution of nonvolatile solute, boiling point elevation ΔTb is given by:

• ΔTb = Kb · m
• ΔTb = Kf · m
• ΔTb = π / RT
• ΔTb = xsolute · Tb°

Correct Answer: ΔTb = Kb · m

Q24. If xA = 0.70 and PA° = 200 torr, what is pA in an ideal solution?

• 140 torr
• 70 torr
• 200 torr
• 260 torr

Correct Answer: 140 torr

Q25. Which statement is correct about vapor and liquid composition in ideal binary mixtures?

• Vapor composition equals liquid composition always
• Vapor composition is richer in the more volatile component
• Liquid composition is richer in the more volatile component
• No relationship exists between them

Correct Answer: Vapor composition is richer in the more volatile component

Q26. Which is a necessary condition for ideal solution behavior at molecular level?

• A–B interactions much stronger than A–A and B–B
• A–B interactions similar to A–A and B–B
• A and B must be ionic
• One component must be polymeric

Correct Answer: A–B interactions similar to A–A and B–B

Q27. The standard state chemical potential μi° used in ideal solution expressions refers to:

• Pure component i at the same T and P
• Infinite dilution reference
• Gas phase at 1 atm only
• Zero concentration

Correct Answer: Pure component i at the same T and P

Q28. Which is true about entropy of mixing for ideal solutions?

• It is zero
• It is negative
• It is positive and given by −R Σ xi ln xi
• It equals ΔmixH

Correct Answer: It is positive and given by −R Σ xi ln xi

Q29. In an ideal binary solution, fugacity of component i in the liquid is related to its pure-component fugacity by:

• fi = xi · fi°
• fi = fi° / xi
• fi = fi° + xi
• fi = xi² · fi°

Correct Answer: fi = xi · fi°

Q30. Which experimental observation suggests ideal behavior?

• Significant excess volume on mixing
• Measured vapor pressures follow linear x dependence with composition
• Large deviation of activity coefficients from unity
• Formation of azeotrope

Correct Answer: Measured vapor pressures follow linear x dependence with composition

Q31. For a solution obeying Raoult’s law, the vapor pressure of pure component A at temperature T is 300 mmHg. If xA = 0.4, what is pA?

• 120 mmHg
• 300 mmHg
• 750 mmHg
• 0 mmHg

Correct Answer: 120 mmHg

Q32. Which property is NOT colligative?

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

Correct Answer: Refractive index change

Q33. The van’t Hoff factor (i) accounts for:

• Nonideality of solvents only
• Degree of dissociation or association of solute particles
• Temperature dependence of vapor pressure
• Change in surface tension

Correct Answer: Degree of dissociation or association of solute particles

Q34. In an ideal solution, which of the following is true for excess Gibbs energy (G^E)?

• G^E > 0 for all mixtures
• G^E < 0 for all mixtures
• G^E = 0 at all compositions
• G^E equals ΔmixH

Correct Answer: G^E = 0 at all compositions

Q35. When applying Raoult’s law to both components in a binary mixture, what assumption is made about the vapor phase?

• Vapor behaves as an ideal gas mixture
• Vapor pressure is independent of composition
• Vapor is a perfect liquid
• Vapor composition is identical to liquid composition

Correct Answer: Vapor behaves as an ideal gas mixture

Q36. Which measurement can help determine whether a pharmaceutical binary mixture is ideal?

• Boiling point vs composition curve and comparison with Raoult’s law predictions
• Colorimetric assay alone
• pH measurement only
• Optical rotation only

Correct Answer: Boiling point vs composition curve and comparison with Raoult’s law predictions

Q37. For a nonvolatile solute in an ideal solvent, the vapor pressure above the solution equals:

• xsolute · P°solvent
• xsolvent · P°solvent
• P°solvent / xsolvent
• P°solute

Correct Answer: xsolvent · P°solvent

Q38. Which of the following indicates stronger A–B attraction relative to A–A and B–B?

• Positive deviation from Raoult’s law
• Negative deviation from Raoult’s law
• Zero vapor pressure
• Infinite boiling point

Correct Answer: Negative deviation from Raoult’s law

Q39. In pharmaceutical freezing point depression experiments, using an ideal solution approximation helps to:

• Exact determination of ionic strength regardless of dissociation
• Estimate molar mass of unknown non-electrolyte solute from ΔTf
• Measure viscosity changes precisely
• Predict drug stability at any pH

Correct Answer: Estimate molar mass of unknown non-electrolyte solute from ΔTf

Q40. Which expression gives mole fraction of solute for very dilute nonvolatile solute when using relative lowering of vapor pressure?

• ΔP / P° ≈ xsolute
• ΔP / P° ≈ xsolvent
• P / P° ≈ xsolute
• ΔP ≈ xsolute · P

Correct Answer: ΔP / P° ≈ xsolute

Q41. Partial molar volume of component i is defined as:

• Vi = total volume / number of moles
• ∂V/∂ni at constant T, P and other nj
• Volume of pure component at STP
• Vapor volume of i

Correct Answer: ∂V/∂ni at constant T, P and other nj

Q42. Which of the following is an experimental signature of ideal behavior in vapour-liquid equilibrium?

• Constant boiling mixture (azeotrope)
• Linear relationship between partial pressure and mole fraction across range
• Large curvature in P–x plot
• Activity coefficients far from unity

Correct Answer: Linear relationship between partial pressure and mole fraction across range

Q43. In dilute solutions, which concentration unit is used in the van’t Hoff osmotic pressure equation π = iMRT?

• Molality (m)
• Molarity (M)
• Mole fraction (x)
• Mass percent

Correct Answer: Molarity (M)

Q44. If an ideal binary mixture has components with vapor pressures PA° = 400 mmHg and PB° = 200 mmHg and xA = 0.25, what is Ptot?

• 300 mmHg
• 250 mmHg
• 150 mmHg
• 50 mmHg

Correct Answer: 250 mmHg

Q45. Which statement best describes how colligative properties aid drug formulation?

• They depend on chemical identity of solute, useful for active ingredient selection
• They depend on number of solute particles, helping control osmolarity and stability
• They only affect color and odor of formulations
• They are irrelevant for intravenous solutions

Correct Answer: They depend on number of solute particles, helping control osmolarity and stability

Q46. Which law merges with Raoult’s law for solvent at high concentrations of solute approaching pure solvent?

• Henry’s law for solute at infinite dilution
• Dalton’s law for gases
• Fick’s law for diffusion
• Arrhenius equation

Correct Answer: Henry’s law for solute at infinite dilution

Q47. In terms of intermolecular forces, ideal solution behavior most closely requires:

• Hydrogen bonding between unlike molecules only
• Similar magnitude of cohesive forces within and between components
• Only ionic interactions
• Complete immiscibility

Correct Answer: Similar magnitude of cohesive forces within and between components

Q48. Which expression correctly gives mole fraction of solvent in terms of solute mole fraction?

• xsolvent = 1 − xsolute
• xsolvent = xsolute / 2
• xsolvent = 1 + xsolute
• xsolvent = xsolute²

Correct Answer: xsolvent = 1 − xsolute

Q49. In practice, why might an assumed ideal solution model fail for a pharmaceutical binary mixture?

• Because temperature is always constant
• Because specific solute–solvent interactions (hydrogen bonding, ion-dipole) create nonideality
• Because Raoult’s law never applies to liquids
• Because ideal models ignore gravity

Correct Answer: Because specific solute–solvent interactions (hydrogen bonding, ion-dipole) create nonideality

Q50. For an ideal solution, which treatment allows calculation of vapor composition yi from partial pressures?

• yi = xi / (xA + xB)
• yi = pi / Ptot
• yi = xi · Ptot
• yi = Ptot / pi

Correct Answer: yi = pi / Ptot

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