Here below some basic MCQ’s about “Raoult’s law and Colligative properties” with answer explanation. Let’s check one by one which is given below.
1. Raoult’s Law is applicable to which of the following solutions?
a) Ideal solutions
b) Non-ideal solutions
c) Saturated solutions
d) Supersaturated solutions
Answer: a) Ideal solutions
Explanation:
Raoult’s Law states that the partial vapor pressure of each volatile component in a solution is directly proportional to its mole fraction in the solution. This law is applicable only to ideal solutions where there are no significant interactions between different molecules. In ideal solutions, intermolecular forces between different components are similar to those between molecules of the same component.
2. Which of the following is not a colligative property?
a) Relative lowering of vapor pressure
b) Boiling point elevation
c) Osmotic pressure
d) Viscosity
Answer: d) Viscosity
Explanation:
Colligative properties depend on the number of solute particles in a solution and not on their nature. The four main colligative properties are relative lowering of vapor pressure, boiling point elevation, freezing point depression, and osmotic pressure. Viscosity is a property that depends on the nature of the solute and solvent, and is therefore not a colligative property.
3. Which of the following correctly represents the relative lowering of vapor pressure (RLVP) according to Raoult’s law?
a) RLVP = (P₁ – P₁°) / P₁
b) RLVP = x₂
c) RLVP = P₁° / P₁
d) RLVP = x₁
Answer: b) RLVP = x₂
Explanation:
According to Raoult’s law, the relative lowering of vapor pressure is given by the ratio of the decrease in vapor pressure to the original vapor pressure of the solvent. This is equal to the mole fraction of the solute (x₂) in the solution.
4. Which colligative property is used to determine molar mass of polymers?
a) Relative lowering of vapor pressure
b) Elevation of boiling point
c) Depression in freezing point
d) Osmotic pressure
Answer: d) Osmotic pressure
Explanation:
Osmotic pressure is particularly useful in determining the molar mass of large molecules like polymers because small differences in osmotic pressure are more easily measured than small changes in freezing point or boiling point, especially when dealing with large molecules.
5. Elevation in boiling point is directly proportional to which of the following?
a) Molarity of the solution
b) Molality of the solution
c) Mass of the solute
d) Volume of the solvent
Answer: b) Molality of the solution
Explanation:
The elevation in boiling point is a colligative property and is directly proportional to the molality of the solution (number of moles of solute per kilogram of solvent). The relationship is given by ΔTb=Kb×m, where Kb is the ebullioscopic constant and mm is the molality.
6. The depression in freezing point is given by which formula?
a) ΔTf=Kf×M
b) ΔTf=Kf×m
c) ΔTf=Kb×M
d) ΔTf=Kb×m
Answer: b) ΔTf=Kf×m
Explanation:
Depression in freezing point (ΔTf) is a colligative property that is directly proportional to the molality (m) of the solution, where Kf is the cryoscopic constant. The formula is ΔTf=Kf×m, similar to the boiling point elevation formula but specific to freezing.
7. Which of the following is NOT true for ideal solutions?
a) They follow Raoult’s law at all concentrations
b) They have zero enthalpy change on mixing
c) The volume change on mixing is zero
d) They exhibit positive deviation from Raoult’s law
Answer: d) They exhibit positive deviation from Raoult’s law
Explanation:
Ideal solutions follow Raoult’s law at all concentrations, have no enthalpy change, and exhibit no volume change upon mixing. Solutions that show positive or negative deviation from Raoult’s law are considered non-ideal.
8. In an ideal solution, the total vapor pressure is dependent on which of the following?
a) The mole fractions of both components
b) The vapor pressure of the solute
c) The temperature only
d) The vapor pressure of the solvent only
Answer: a) The mole fractions of both components
Explanation:
In an ideal solution, the total vapor pressure depends on the mole fractions of both the solvent and solute. According to Raoult’s law, the partial vapor pressures of each component are proportional to their mole fractions in the solution.
9. Which colligative property is useful in the preservation of food by adding salt or sugar?
a) Relative lowering of vapor pressure
b) Boiling point elevation
c) Depression of freezing point
d) Osmotic pressure
Answer: d) Osmotic pressure
Explanation:
Osmotic pressure is used to preserve food. The addition of salt or sugar creates a hypertonic environment, drawing water out of microorganisms (via osmosis), thus preventing their growth and prolonging the shelf life of the food.
10. Which of the following factors does NOT affect the colligative properties of a solution?
a) Number of solute particles
b) Nature of the solute particles
c) Molality of the solute
d) Temperature of the solution
Answer: b) Nature of the solute particles
Explanation:
Colligative properties depend only on the number of solute particles (whether ions or molecules) in the solution, not on their nature. The type of solute particles does not affect these properties as long as the number of particles remains constant.
11. Boiling point elevation is dependent on which constant?
a) Cryoscopic constant
b) Osmotic constant
c) Ebullioscopic constant
d) Solubility constant
Answer: c) Ebullioscopic constant
Explanation:
The boiling point elevation is dependent on the ebullioscopic constant (KbKb), which is a property specific to the solvent and represents the increase in boiling point per unit molality of a non-volatile solute.
12. Which of the following statements is true regarding osmotic pressure?
a) It decreases with an increase in temperature
b) It increases with an increase in the number of solute particles
c) It is independent of the molarity of the solution
d) It decreases with an increase in solute concentration
Answer: b) It increases with an increase in the number of solute particles
Explanation:
Osmotic pressure increases as the number of solute particles in the solution increases, which means that the greater the concentration of solute, the higher the osmotic pressure. It also increases with temperature, as predicted by van’t Hoff’s equation for osmotic pressure.
13. The van’t Hoff factor (i) for NaCl in an aqueous solution is approximately:
a) 1
b) 2
c) 3
d) 4
Answer: b) 2
Explanation:
Sodium chloride (NaCl) dissociates completely into two ions (Na⁺ and Cl⁻) in aqueous solution, so the van’t Hoff factor ii is 2, reflecting the number of particles produced per formula unit of solute.
14. If the molality of a solution is doubled, the freezing point depression will:
a) Remain the same
b) Be halved
c) Be doubled
d) Become zero
Answer: c) Be doubled
Explanation:
Freezing point depression (ΔTf) is directly proportional to the molality of the solution. If the molality is doubled, the depression in freezing point will also double.
15. A solution has a freezing point depression of 1.86°C. If the cryoscopic constant (KfKf) for water is 1.86°C/m, what is the molality of the solution?
a) 1 m
b) 2 m
c) 0.5 m
d) 3 m
Answer: a) 1 m
Explanation:
The freezing point depression is given by ΔTf=Kf×m. Here, ΔTf=1.86°C and Kf=1.86°C/m, so the molality m is 1 mol/kg.
16. The osmotic pressure of a solution is directly proportional to the:
a) Volume of the solution
b) Number of solute particles
c) Temperature only
d) Vapor pressure of the solvent
Answer: b) Number of solute particles
Explanation:
Osmotic pressure is directly proportional to the number of solute particles in a given volume of solution, as well as temperature. This is described by van’t Hoff’s law: Π=iMRTΠ=iMRT, where ΠΠ is the osmotic pressure, MM is molarity, RR is the gas constant, and TT is temperature.
17. Which of the following is an example of a solution that shows negative deviation from Raoult’s law?
a) Benzene and toluene
b) Acetone and chloroform
c) Ethanol and water
d) Hexane and heptane
Answer: b) Acetone and chloroform
Explanation:
Solutions that show negative deviation from Raoult’s law have stronger intermolecular interactions between the different components than between the molecules of each component alone. Acetone and chloroform exhibit such strong interactions (e.g., hydrogen bonding), leading to a lower vapor pressure than expected.
18. Which of the following is NOT a characteristic of a non-ideal solution?
a) Positive or negative deviation from Raoult’s law
b) Significant enthalpy change on mixing
c) Follow Raoult’s law at all concentrations
d) Non-zero volume change on mixing
Answer: c) Follow Raoult’s law at all concentrations
Explanation:
Non-ideal solutions do not follow Raoult’s law at all concentrations because they show deviations due to either stronger or weaker intermolecular forces between different components. Ideal solutions follow Raoult’s law under all conditions.
19. Which of the following can cause a solution to show positive deviation from Raoult’s law?
a) Strong attractive forces between solute and solvent
b) Weak attractive forces between solute and solvent
c) Hydrogen bonding between solute and solvent
d) Formation of an azeotrope
Answer: b) Weak attractive forces between solute and solvent
Explanation:
Positive deviation from Raoult’s law occurs when the intermolecular forces between solute and solvent are weaker than those between like molecules. This results in higher vapor pressures than predicted by Raoult’s law.
20. Which of the following terms is used to describe a solution that exhibits zero enthalpy and volume change upon mixing?
a) Ideal solution
b) Azeotropic solution
c) Non-ideal solution
d) Dilute solution
Answer: a) Ideal solution
Explanation:
An ideal solution exhibits no change in enthalpy (ΔHmix=0) and no change in volume (ΔVmix=0) upon mixing, meaning that the intermolecular forces between the solute and solvent are similar to those within each pure substance.
21. Which of the following is the van’t Hoff factor for K₂SO₄ in aqueous solution?
a) 2
b) 3
c) 1
d) 4
Answer: b) 3
Explanation:
Potassium sulfate (K₂SO₄) dissociates in water into 2 potassium ions (K⁺) and 1 sulfate ion (SO₄²⁻), resulting in a total of 3 ions. Therefore, the van’t Hoff factor ii for K₂SO₄ is 3.
22. Which of the following statements about colligative properties is correct?
a) Colligative properties are dependent on the chemical identity of the solute.
b) Colligative properties are dependent on the number of solute particles in the solution.
c) Colligative properties apply only to electrolytes.
d) Colligative properties depend on the molar mass of the solute.
Answer: b) Colligative properties are dependent on the number of solute particles in the solution.
Explanation:
Colligative properties (e.g., boiling point elevation, freezing point depression) depend on the concentration and number of solute particles in the solution, not on their chemical identity.
23. A solution exhibits a boiling point higher than that of the pure solvent. This is due to:
a) Decreased vapor pressure of the solvent in the solution
b) Increased vapor pressure of the solvent in the solution
c) Increased volume of the solution
d) Increased molarity of the solvent
Answer: a) Decreased vapor pressure of the solvent in the solution
Explanation:
Boiling point elevation occurs because the vapor pressure of the solvent decreases when a non-volatile solute is added, requiring a higher temperature for the vapor pressure to equal atmospheric pressure.
24. Which of the following can be used to calculate the molar mass of an unknown solute?
a) Osmotic pressure
b) Freezing point depression
c) Boiling point elevation
d) All of the above
Answer: d) All of the above
Explanation:
Molar mass of an unknown solute can be determined using any of the colligative properties (osmotic pressure, freezing point depression, or boiling point elevation), as all these properties are related to the number of solute particles in the solution.
25. When a non-volatile solute is added to a solvent, which of the following properties decreases?
a) Boiling point
b) Freezing point
c) Osmotic pressure
d) Vapor pressure
Answer: d) Vapor pressure
Explanation:
The addition of a non-volatile solute lowers the vapor pressure of the solvent because fewer solvent molecules are available to escape into the vapor phase. As a result, the vapor pressure of the solution is lower than that of the pure solvent.
26. Which of the following represents the correct relationship between boiling point elevation and the molality of a solution?
a) ΔTb=Kf×m
b) ΔTb=Kb×m
c) ΔTb=Kb×M
d) ΔTb=Kf×M
Answer: b) ΔTb=Kb×m
Explanation:
Boiling point elevation is directly proportional to the molality of the solution (mm) and the ebullioscopic constant (Kb). The formula is ΔTb=Kb×m, where ΔTb is the boiling point elevation.
27. If the freezing point of a solution decreases by 5°C when a non-volatile solute is added, what would happen to the boiling point of the same solution?
a) It would decrease
b) It would increase
c) It would remain the same
d) It would depend on the nature of the solute
Answer: b) It would increase
Explanation:
The addition of a non-volatile solute causes a depression in the freezing point and an elevation in the boiling point. Both effects are colligative properties that depend on the number of solute particles in the solution.
28. Which of the following equations represents osmotic pressure (Π) for a dilute solution?
a) Π=iMRT
b) Π=nRT/V
c) Π=P1−P2
d) Π=iKf×m
Answer: a) Π=iMRT
Explanation:
Osmotic pressure (Π) is given by the equation Π=iMRT where i is the van’t Hoff factor, M is the molarity of the solution, R is the gas constant, and T is the absolute temperature.
29. Which of the following solutions will have the highest boiling point?
a) 1 M NaCl
b) 1 M glucose
c) 1 M BaCl₂
d) 1 M urea
Answer: c) 1 M BaCl₂
Explanation:
The boiling point elevation is higher for solutions with more solute particles. BaCl₂ dissociates into 3 ions (Ba²⁺ and 2 Cl⁻), leading to a higher number of particles in solution compared to NaCl (2 ions), glucose (no dissociation), and urea (no dissociation). Hence, 1 M BaCl₂ will have the highest boiling point.
30. Which of the following solutions will exhibit the highest freezing point depression?
a) 0.1 M KCl
b) 0.1 M glucose
c) 0.1 M CaCl₂
d) 0.1 M urea
Answer: c) 0.1 M CaCl₂
Explanation:
Freezing point depression is greater for solutions with more solute particles. CaCl₂ dissociates into 3 ions (Ca²⁺ and 2 Cl⁻), which means it produces more particles than KCl (2 ions), glucose, or urea (no dissociation). Thus, 0.1 M CaCl₂ will show the highest freezing point depression.
31. The cryoscopic constant (Kf) of water is 1.86°C·kg/mol. If 0.5 mol of NaCl is dissolved in 1 kg of water, what is the freezing point depression of the solution? (Assume complete dissociation of NaCl, i=2)
a) 1.86°C
b) 2.79°C
c) 3.72°C
d) 5.58°C
Answer: c) 3.72°C
Explanation:
Freezing point depression is calculated using ΔTf=i×Kf×m
32. Which of the following represents an ideal solution?
a) Benzene and methanol
b) Acetone and chloroform
c) Benzene and toluene
d) Ethanol and water
Answer: c) Benzene and toluene
Explanation:
Ideal solutions follow Raoult’s law at all concentrations. Benzene and toluene have similar structures and intermolecular forces, making them behave ideally when mixed. Other combinations like ethanol and water or acetone and chloroform show deviations due to hydrogen bonding or strong interactions.
33. Which colligative property is used to determine the molar mass of biomolecules like proteins?
a) Boiling point elevation
b) Freezing point depression
c) Relative lowering of vapor pressure
d) Osmotic pressure
Answer: d) Osmotic pressure
Explanation:
Osmotic pressure is commonly used to determine the molar mass of large biomolecules like proteins, as small changes in osmotic pressure are easier to measure than other colligative properties for such large molecules.
34. In an aqueous solution, which of the following solutes will have the greatest impact on the colligative properties of the solution?
a) 1 M glucose
b) 1 M NaCl
c) 1 M urea
d) 1 M K₃[Fe(CN)₆]
Answer: d) 1 M K₃[Fe(CN)₆]
Explanation:
The more particles a solute dissociates into, the greater its impact on colligative properties. K₃[Fe(CN)₆] dissociates into 4 ions (3 K⁺ and 1 Fe(CN)₆³⁻), which affects colligative properties more significantly than NaCl (2 ions), glucose, and urea (no dissociation).
35. What is the van’t Hoff factor (i) for aluminum chloride (AlCl₃) in an aqueous solution?
a) 1
b) 2
c) 3
d) 4
Answer: d) 4
Explanation:
Aluminum chloride (AlCl₃) dissociates completely in water into one Al³⁺ ion and three Cl⁻ ions, giving a total of 4 particles. Therefore, the van’t Hoff factor for AlCl₃ is 4.
36. Which of the following explains why a non-volatile solute lowers the vapor pressure of a solvent?
a) The solute occupies the surface area, reducing the number of solvent molecules that can escape into vapor
b) The solute decreases the temperature of the solvent
c) The solute increases the molecular interactions between solvent particles
d) The solute increases the vapor pressure of the solvent
Answer: a) The solute occupies the surface area, reducing the number of solvent molecules that can escape into vapor
Explanation:
When a non-volatile solute is added to a solvent, it occupies some of the surface area, reducing the number of solvent molecules that can escape into the vapor phase, which lowers the vapor pressure of the solvent.
37. What is the effect of adding a non-volatile solute to a solvent on the boiling point of the solution?
a) It lowers the boiling point
b) It raises the boiling point
c) It has no effect on the boiling point
d) It lowers the vapor pressure but not the boiling point
Answer: b) It raises the boiling point
Explanation:
Adding a non-volatile solute to a solvent raises the boiling point of the solution. This phenomenon, known as boiling point elevation, occurs because the solute reduces the vapor pressure of the solvent, requiring a higher temperature for the vapor pressure to reach atmospheric pressure.
38. Which property remains unchanged when a solute is added to a solvent?
a) Boiling point
b) Freezing point
c) Vapor pressure
d) Molar mass of the solvent
Answer: d) Molar mass of the solvent
Explanation:
Adding a solute to a solvent changes properties like boiling point, freezing point, and vapor pressure (colligative properties), but the molar mass of the solvent remains unchanged as it is an intrinsic property of the solvent.
39. If the boiling point of a solution is 101°C and the solvent is water, what is the approximate molality of the solution if the ebullioscopic constant (Kb) of water is 0.52°C/m?
a) 1 m
b) 2 m
c) 0.5 m
d) 0.96 m
Answer: d) 0.96 m
40. For a solution exhibiting positive deviation from Raoult’s law, which of the following statements is correct?
a) The vapor pressure of the solution is higher than expected
b) The vapor pressure of the solution is lower than expected
c) The solution exhibits a freezing point lower than expected
d) The solute and solvent exhibit strong attractive forces
Answer: a) The vapor pressure of the solution is higher than expected
Explanation:
Positive deviation from Raoult’s law occurs when the vapor pressure of the solution is higher than expected because the interactions between solute and solvent molecules are weaker than those between the solvent molecules in the pure state.
41. Which of the following factors can affect osmotic pressure?
a) Temperature
b) Solute concentration
c) Nature of the solute particles
d) Both a and b
Answer: d) Both a and b
Explanation:
Osmotic pressure depends on both temperature and the concentration of solute particles. According to the van’t Hoff equation (Π=iMRT), osmotic pressure increases with an increase in solute concentration or temperature.
42. The cryoscopic constant (KfKf) of a solvent is:
a) The freezing point of the solvent
b) The increase in boiling point per molality of the solute
c) The depression in freezing point per molality of the solute
d) The vapor pressure lowering per mole fraction of solute
Answer: c) The depression in freezing point per molality of the solute
Explanation:
The cryoscopic constant (KfKf) represents the freezing point depression per molality of solute added to the solvent. It is specific to each solvent and is used to calculate the change in freezing point when a solute is dissolved.
43. The molar mass of a solute can be determined from which of the following properties?
a) Boiling point of the solution
b) Freezing point of the solution
c) Osmotic pressure of the solution
d) All of the above
Answer: d) All of the above
Explanation:
The molar mass of a solute can be determined from colligative properties such as boiling point elevation, freezing point depression, or osmotic pressure, as these depend on the number of solute particles in the solution.
44. What is the van’t Hoff factor (ii) for sucrose in an aqueous solution?
a) 1
b) 2
c) 3
d) 4
Answer: a) 1
Explanation:
Sucrose is a non-electrolyte and does not dissociate into ions in solution. Therefore, the van’t Hoff factor (ii) for sucrose is 1.
45. In an aqueous solution, which of the following will produce the lowest freezing point?
a) 0.1 M NaCl
b) 0.1 M CaCl₂
c) 0.1 M glucose
d) 0.1 M urea
Answer: b) 0.1 M CaCl₂
Explanation:
Freezing point depression depends on the number of solute particles. CaCl₂ dissociates into 3 ions (1 Ca²⁺ and 2 Cl⁻), producing more particles than NaCl (2 ions), glucose, or urea (no dissociation). Hence, 0.1 M CaCl₂ will have the greatest effect on freezing point depression.
46. Which of the following solutions will have the highest vapor pressure?
a) 1 M NaCl
b) 1 M glucose
c) 1 M K₂SO₄
d) 1 M CaCl₂
Answer: b) 1 M glucose
Explanation:
Vapor pressure lowering is a colligative property and depends on the number of solute particles. Glucose is a non-electrolyte and does not dissociate, so it will have the fewest solute particles in solution, resulting in the highest vapor pressure compared to the dissociating electrolytes (NaCl, K₂SO₄, and CaCl₂).
47. Which of the following factors increases the magnitude of colligative properties?
a) Lower solute concentration
b) Non-electrolyte solutes
c) Electrolytes that dissociate completely
d) Decrease in temperature
Answer: c) Electrolytes that dissociate completely
Explanation:
Colligative properties are directly related to the number of particles in solution. Electrolytes that dissociate completely produce more ions, increasing the magnitude of colligative properties like boiling point elevation, freezing point depression, and osmotic pressure.
48. Which of the following is a colligative property?
a) Surface tension
b) Viscosity
c) Freezing point depression
d) Density
Answer: c) Freezing point depression
Explanation:
Colligative properties are those that depend on the number of solute particles but not on their identity. Freezing point depression is a classic example of a colligative property.
50. Which of the following will exhibit negative deviation from Raoult’s law?
a) Benzene and toluene
b) Ethanol and water
c) Acetone and chloroform
d) Methanol and hexane
Answer: c) Acetone and chloroform
Explanation:
Negative deviation from Raoult’s law occurs when the intermolecular forces between the solute and solvent are stronger than those in the pure components. Acetone and chloroform form hydrogen bonds, leading to negative deviation.
51. If 1 mole of a non-electrolyte solute is dissolved in 1 kg of water, what is the freezing point depression of the solution? (Cryoscopic constant of water, Kf=1.86°C⋅kg/mol)
a) 1.86°C
b) 3.72°C
c) 5.58°C
d) 0.93°C
Answer: a) 1.86°C
Explanation:
The freezing point depression is calculated using ΔTf=Kf×m
52. Which of the following solutions will have the lowest freezing point?
a) 0.1 M glucose
b) 0.1 M NaCl
c) 0.1 M K₂SO₄
d) 0.1 M urea
Answer: c) 0.1 M K₂SO₄
Explanation:
The freezing point depression depends on the number of particles in solution. K₂SO₄ dissociates into 3 ions (2 K⁺ and 1 SO₄²⁻), producing more particles than NaCl (2 ions) and glucose or urea (which do not dissociate). Therefore, 0.1 M K₂SO₄ will have the lowest freezing point.
53. In a solution that follows Raoult’s law, the vapor pressure of a solvent is:
a) Higher than in the pure solvent
b) Lower than in the pure solvent
c) Equal to that of the solute
d) Independent of the solvent’s mole fraction
Answer: b) Lower than in the pure solvent
Explanation:
According to Raoult’s law, the vapor pressure of a solvent in a solution is proportional to its mole fraction. Since the mole fraction of the solvent in a solution is always less than 1, the vapor pressure in a solution is lower than that of the pure solvent.
54. Which colligative property is most effective for determining the molar mass of polymers?
a) Boiling point elevation
b) Freezing point depression
c) Osmotic pressure
d) Vapor pressure lowering
Answer: c) Osmotic pressure
Explanation:
Osmotic pressure is the most sensitive colligative property for determining the molar mass of large molecules like polymers. Small changes in concentration lead to significant changes in osmotic pressure, making it easier to measure for high molar mass substances.
55. What is the freezing point depression if 2 mol of NaCl is dissolved in 1 kg of water? (Assume complete dissociation, i=2, Kf=1.86°C⋅kg/mol)
a) 1.86°C
b) 3.72°C
c) 7.44°C
d) 9.30°C
Answer: c) 7.44°C
Explanation:
The freezing point depression is calculated using ΔTf=i×Kf×m
56. Which of the following solutions will have the lowest vapor pressure?
a) 1 M NaCl
b) 1 M glucose
c) 1 M BaCl₂
d) 1 M urea
Answer: c) 1 M BaCl₂
Explanation:
Vapor pressure lowering depends on the number of solute particles. BaCl₂ dissociates into 3 ions (Ba²⁺ and 2 Cl⁻), producing more particles than NaCl (2 ions), glucose, and urea (which do not dissociate). Therefore, 1 M BaCl₂ will have the lowest vapor pressure.
57. Which of the following statements about ideal solutions is correct?
a) Ideal solutions show positive deviation from Raoult’s law
b) Ideal solutions follow Raoult’s law at all concentrations
c) Ideal solutions have strong intermolecular forces between solute and solvent
d) Ideal solutions exhibit changes in enthalpy upon mixing
Answer: b) Ideal solutions follow Raoult’s law at all concentrations
Explanation:
An ideal solution obeys Raoult’s law over the entire range of concentrations. The intermolecular forces between the solute and solvent are similar to those in the pure components, so there is no enthalpy change upon mixing.
58. A solution of a non-volatile solute in a volatile solvent has a vapor pressure:
a) Equal to that of the pure solvent
b) Higher than that of the pure solvent
c) Lower than that of the pure solvent
d) Equal to that of the solute
Answer: c) Lower than that of the pure solvent
Explanation:
The vapor pressure of a solution containing a non-volatile solute is lower than that of the pure solvent. This is because the non-volatile solute reduces the number of solvent molecules that can escape into the vapor phase, thus lowering the vapor pressure.
59. Which of the following can be used to calculate the van’t Hoff factor (ii)?
a) Freezing point depression
b) Boiling point elevation
c) Osmotic pressure
d) All of the above
Answer: d) All of the above
Explanation:
The van’t Hoff factor (ii) can be calculated using any colligative property, such as freezing point depression, boiling point elevation, or osmotic pressure, as all of these properties depend on the number of particles in the solution.
60. Which of the following solutions will have the highest boiling point?
a) 1 M NaCl
b) 1 M glucose
c) 1 M BaCl₂
d) 1 M urea
Answer: c) 1 M BaCl₂
Explanation:
The boiling point elevation depends on the number of particles in solution. BaCl₂ dissociates into 3 ions, producing more particles than NaCl (2 ions), glucose, and urea (which do not dissociate), resulting in a higher boiling point for the BaCl₂ solution.
61. Which of the following mixtures shows positive deviation from Raoult’s law?
a) Acetone and chloroform
b) Ethanol and water
c) Carbon disulfide and acetone
d) Benzene and toluene
Answer: c) Carbon disulfide and acetone
Explanation:
Positive deviation from Raoult’s law occurs when the interactions between the solute and solvent molecules are weaker than those in the pure components, resulting in higher vapor pressure than expected. Carbon disulfide and acetone show this behavior.
63. What is the van’t Hoff factor (ii) for Na₂SO₄ in aqueous solution?
a) 2
b) 3
c) 1
d) 4
Answer: b) 3
Explanation:
Sodium sulfate (Na₂SO₄) dissociates into 2 Na⁺ ions and 1 SO₄²⁻ ion in aqueous solution, giving a total of 3 ions. Therefore, the van’t Hoff factor (ii) for Na₂SO₄ is 3.
64. The colligative property of freezing point depression is most pronounced for which of the following?
a) 1 M glucose
b) 1 M NaCl
c) 1 M BaCl₂
d) 1 M K₃PO₄
Answer: d) 1 M K₃PO₄
Explanation:
The freezing point depression is more significant when there are more particles in solution. K₃PO₄ dissociates into 4 ions (3 K⁺ and 1 PO₄³⁻), making its effect on freezing point depression greater than the other solutes.
65. Which of the following statements is true for a solution of a non-volatile solute in a volatile solvent?
a) The vapor pressure of the solution is equal to that of the solvent
b) The freezing point of the solution is higher than that of the pure solvent
c) The boiling point of the solution is lower than that of the pure solvent
d) The vapor pressure of the solution is lower than that of the pure solvent
Answer: d) The vapor pressure of the solution is lower than that of the pure solvent
Explanation:
Adding a non-volatile solute to a volatile solvent lowers the vapor pressure of the solution. The solute particles reduce the number of solvent molecules escaping into the vapor phase, resulting in a lower vapor pressure.
66. What will be the boiling point elevation of a solution of 1 molal NaCl in water? (Assume complete dissociation, i=2, Kb=0.52°C⋅kg/mol)
a) 0.52°C
b) 1.04°C
c) 0.26°C
d) 2.08°C
Answer: b) 1.04°C
Explanation:
The boiling point elevation is calculated using ΔTb=i×Kb×m
67. Which of the following represents the relationship between vapor pressure lowering and mole fraction of solute?
a) ΔP=PA0×xB
b) ΔP=PA0×xA
c) ΔP=PB0×xA
d) ΔP=PB0×xB
Answer: a) ΔP=PA0×xB
Explanation:
Raoult’s law for vapor pressure lowering states that the lowering in vapor pressure (ΔP) is proportional to the vapor pressure of the pure solvent (PA0) and the mole fraction of the solute (xB).
68. In an ideal solution, the enthalpy of mixing is:
a) Positive
b) Negative
c) Zero
d) Infinite
Answer: c) Zero
Explanation:
In an ideal solution, the enthalpy of mixing is zero because the interactions between the solute and solvent molecules are similar to those in the pure components, resulting in no heat being absorbed or released during mixing.
69. Which of the following solutions shows negative deviation from Raoult’s law?
a) Acetone and carbon tetrachloride
b) Ethanol and benzene
c) Acetone and chloroform
d) Water and urea
Answer: c) Acetone and chloroform
Explanation:
Negative deviation occurs when the interactions between solute and solvent are stronger than those in the pure components. Acetone and chloroform exhibit hydrogen bonding, leading to stronger interactions and negative deviation from Raoult’s law.
70. The relative lowering of vapor pressure for a solution is directly proportional to:
a) The temperature of the solution
b) The mole fraction of the solute
c) The molality of the solute
d) The vapor pressure of the solute
Answer: b) The mole fraction of the solute
Explanation:
According to Raoult’s law, the relative lowering of vapor pressure is directly proportional to the mole fraction of the solute in the solution. This relationship is key to understanding how solutes affect the vapor pressure of solvents.
71. Which of the following solutions will have the highest boiling point?
a) 0.1 M NaCl
b) 0.1 M glucose
c) 0.1 M urea
d) 0.1 M BaCl₂
Answer: d) 0.1 M BaCl₂
Explanation:
The boiling point elevation depends on the number of particles in the solution. BaCl₂ dissociates into 3 ions (Ba²⁺ and 2 Cl⁻), producing more particles than NaCl (2 ions), glucose, and urea (no dissociation), resulting in a higher boiling point for BaCl₂.
72. Which of the following factors does not affect the freezing point depression?
a) The number of solute particles
b) The identity of the solute particles
c) The molality of the solution
d) The van’t Hoff factor
Answer: b) The identity of the solute particles
Explanation:
Freezing point depression is a colligative property, meaning it depends on the number of solute particles, not their identity. Factors like molality and the van’t Hoff factor, which reflect the number of particles in the solution, do affect freezing point depression.
73. Which of the following mixtures forms an ideal solution?
a) Benzene and toluene
b) Acetone and water
c) Ethanol and water
d) Hexane and ethanol
Answer: a) Benzene and toluene
Explanation:
Ideal solutions follow Raoult’s law and have similar intermolecular forces between solute and solvent. Benzene and toluene have similar structures and interact similarly, making them form an ideal solution.
74. What is the freezing point of a 2 molal solution of NaCl in water? (Assume complete dissociation, i=2, and Kf=1.86°C⋅kg/mol)
a) -1.86°C
b) -3.72°C
c) -7.44°C
d) -5.58°C
Answer: d) -7.44°C
74. What is the freezing point of a 2 molal solution of NaCl in water?
a) -1.86°C
b) -3.72°C
c) -7.44°C
d) -5.58°C
Answer: c) -7.44°C
.
75. Which of the following colligative properties is used in the determination of molar mass of macromolecules such as proteins?
a) Boiling point elevation
b) Freezing point depression
c) Osmotic pressure
d) Vapor pressure lowering
Answer: c) Osmotic pressure
Explanation:
Osmotic pressure is the most sensitive colligative property for determining the molar mass of large molecules, such as proteins. Small concentrations of macromolecules can cause significant changes in osmotic pressure.
76. Which of the following will exhibit the largest freezing point depression for a 1 molal aqueous solution?
a) NaCl
b) K₂SO₄
c) Glucose
d) MgCl₂
Answer: b) K₂SO₄
Explanation:
K₂SO₄ dissociates into 3 ions (2 K⁺ and 1 SO₄²⁻), whereas NaCl dissociates into 2 ions and glucose does not dissociate at all. The freezing point depression depends on the number of particles in the solution, so K₂SO₄ will exhibit the largest depression.
77. Which of the following solutions will have the highest vapor pressure at a given temperature?
a) 0.5 M NaCl
b) 0.5 M urea
c) 0.5 M KNO₃
d) 0.5 M MgCl₂
Answer: b) 0.5 M urea
Explanation:
Urea is a non-electrolyte and does not dissociate, so it contributes fewer solute particles to the solution compared to the electrolytes (NaCl, KNO₃, and MgCl₂), which dissociate into ions. As a result, the solution of urea will have the highest vapor pressure.
78. Which of the following statements about Raoult’s law is correct?
a) It applies only to non-volatile solutes
b) It applies to all types of solutions
c) It is applicable to ideal solutions
d) It is applicable only at high pressures
Answer: c) It is applicable to ideal solutions
Explanation:
Raoult’s law is valid for ideal solutions, where the intermolecular forces between solute and solvent are similar to those in the pure substances. It is not applicable to non-ideal solutions or at high pressures where deviations may occur.
79. For a solution of a non-volatile solute in water, the vapor pressure:
a) Remains the same as pure water
b) Is higher than pure water
c) Is lower than pure water
d) Is independent of the concentration of the solute
Answer: c) Is lower than pure water
Explanation:
When a non-volatile solute is dissolved in a solvent, the vapor pressure of the solution decreases compared to the pure solvent. This occurs because fewer solvent molecules can escape into the vapor phase due to the presence of solute particles.
80. What is the expected van’t Hoff factor (ii) for BaCl₂ in an aqueous solution?
a) 2
b) 3
c) 4
d) 1
Answer: b) 3
Explanation:
BaCl₂ dissociates into 3 ions in solution: one Ba²⁺ ion and two Cl⁻ ions. Therefore, the van’t Hoff factor (i) for BaCl₂ is 3.
81. Which of the following is not a colligative property?
a) Boiling point elevation
b) Osmotic pressure
c) Freezing point depression
d) Surface tension
Answer: d) Surface tension
Explanation:
Surface tension is a property that depends on the nature of the liquid molecules and their interactions, not on the number of solute particles in solution. Therefore, it is not a colligative property.
82. Which of the following solutions will have the highest boiling point?
a) 1 M glucose
b) 1 M NaCl
c) 1 M K₂SO₄
d) 1 M urea
Answer: c) 1 M K₂SO₄
Explanation:
The boiling point elevation depends on the number of solute particles in the solution. K₂SO₄ dissociates into 3 ions (2 K⁺ and 1 SO₄²⁻), producing more particles than NaCl (2 ions), glucose, and urea (which do not dissociate), resulting in a higher boiling point for K₂SO₄.
83. In which of the following solutions will the van’t Hoff factor be 1?
a) NaCl
b) KNO₃
c) Glucose
d) MgCl₂
Answer: c) Glucose
Explanation:
Glucose is a non-electrolyte and does not dissociate in solution, so its van’t Hoff factor (i) is 1. The other compounds are electrolytes and dissociate into ions, leading to i>1.
84. Which of the following solutions will show the least depression in freezing point?
a) 0.1 M NaCl
b) 0.1 M glucose
c) 0.1 M BaCl₂
d) 0.1 M urea
Answer: b) 0.1 M glucose
Explanation:
Glucose is a non-electrolyte and does not dissociate, so it produces fewer particles in solution compared to the electrolytes, resulting in the least depression in freezing point.
85. Raoult’s law is valid for which type of solution?
a) Non-ideal solutions
b) Ideal solutions
c) Concentrated solutions
d) Solutions with strong intermolecular forces
Answer: b) Ideal solutions
Explanation:
Raoult’s law is valid for ideal solutions, where the intermolecular forces between the solute and solvent molecules are similar to those in the pure substances, leading to no enthalpy change on mixing.
86. Which of the following will not cause a deviation from Raoult’s law?
a) Hydrogen bonding between solute and solvent
b) Weak intermolecular forces between solute and solvent
c) Strong solute-solvent interactions
d) Identical solute and solvent molecules
Answer: d) Identical solute and solvent molecules
Explanation:
If the solute and solvent molecules are identical, the solution behaves ideally, and Raoult’s law will hold without any deviation. Deviation occurs when the interactions between solute and solvent are significantly different from those in the pure substances.
87. The van’t Hoff factor (ii) for an electrolyte is:
a) Always less than 1
b) Always equal to 1
c) Always greater than 1
d) Independent of the number of ions
Answer: c) Always greater than 1
Explanation:
For electrolytes, the van’t Hoff factor (ii) is always greater than 1 because they dissociate into more than one ion in solution. The factor reflects the total number of particles produced by dissociation.
88. Which of the following shows positive deviation from Raoult’s law?
a) Water and ethanol
b) Acetone and chloroform
c) Benzene and toluene
d) Ethanol and hexane
Answer: d) Ethanol and hexane
Explanation:
Positive deviation from Raoult’s law occurs when the solute-solvent interactions are weaker than those between the pure components. Ethanol and hexane have weak interactions, leading to higher vapor pressure and positive deviation.
89. Which of the following is an example of a non-ideal solution with negative deviation?
a) Benzene and toluene
b) Ethanol and water
c) Acetone and chloroform
d) Hexane and heptane
Answer: c) Acetone and chloroform
Explanation:
Acetone and chloroform form hydrogen bonds, which are stronger than the interactions in the pure components, leading to a negative deviation from Raoult’s law.
90. Which of the following can be used to calculate molecular weight based on freezing point depression?
a) Raoult’s law
b) van’t Hoff factor
c) Osmotic pressure
d) Cryoscopic constant
Answer: d) Cryoscopic constant
Explanation:
The cryoscopic constant (Kf) is used in the calculation of molecular weight through freezing point depression. By measuring the freezing point depression and knowing Kf, the molar mass of the solute can be determined.
91. Which of the following mixtures is most likely to show a negative deviation from Raoult’s law?
a) Water and ethanol
b) Acetone and benzene
c) Chloroform and acetone
d) Carbon disulfide and acetone
Answer: c) Chloroform and acetone
Explanation:
Chloroform and acetone form strong hydrogen bonds between their molecules, which are stronger than the interactions in the pure components. This leads to a negative deviation from Raoult’s law, where the vapor pressure is lower than expected.
92. For which of the following compounds will the van’t Hoff factor (ii) be greater than 1?
a) Glucose
b) Sucrose
c) NaCl
d) Urea
Answer: c) NaCl
Explanation:
NaCl is an electrolyte and dissociates into Na⁺ and Cl⁻ ions in solution, which results in a van’t Hoff factor greater than 1. Glucose, sucrose, and urea are non-electrolytes and do not dissociate in solution, so their i is 1.
93. The elevation in boiling point of a solution is directly proportional to:
a) The vapor pressure of the solution
b) The molality of the solution
c) The molecular weight of the solute
d) The volume of the solvent
Answer: b) The molality of the solution
Explanation:
The elevation in boiling point (ΔTb) is directly proportional to the molality (m) of the solution according to the equation ΔTb=i×Kb×m, where Kb is the ebullioscopic constant and i is the van’t Hoff factor.
94. Which of the following solutions will have the lowest freezing point?
a) 0.1 M NaCl
b) 0.1 M urea
c) 0.1 M K₂SO₄
d) 0.1 M glucose
Answer: c) 0.1 M K₂SO₄
Explanation:
K₂SO₄ dissociates into 3 ions (2 K⁺ and 1 SO₄²⁻), producing more particles in solution than NaCl (2 ions) and urea and glucose (which do not dissociate). The larger the number of particles, the greater the freezing point depression.
95. Which of the following colligative properties is most useful for determining the molar mass of polymers?
a) Boiling point elevation
b) Freezing point depression
c) Osmotic pressure
d) Vapor pressure lowering
Answer: c) Osmotic pressure
Explanation:
Osmotic pressure is the most sensitive colligative property for determining the molar mass of large molecules like polymers. Small concentrations of these molecules can cause significant osmotic pressure changes.
96. Which of the following compounds would have the highest van’t Hoff factor (ii) in an aqueous solution?
a) NaCl
b) CaCl₂
c) Glucose
d) KNO₃
Answer: b) CaCl₂
Explanation:
CaCl₂ dissociates into 3 ions (1 Ca²⁺ and 2 Cl⁻), whereas NaCl and KNO₃ dissociate into 2 ions each. Glucose does not dissociate. Therefore, CaCl₂ has the highest van’t Hoff factor.
97. Raoult’s law is not obeyed by solutions that exhibit:
a) Ideal behavior
b) Negative deviations
c) Positive deviations
d) Both b and c
Answer: d) Both b and c
Explanation:
Raoult’s law is valid for ideal solutions. Non-ideal solutions that exhibit positive or negative deviations from Raoult’s law do not obey it due to the differing strength of solute-solvent interactions compared to the pure components.
98. Which of the following colligative properties does not depend on temperature?
a) Boiling point elevation
b) Osmotic pressure
c) Freezing point depression
d) Relative lowering of vapor pressure
Answer: d) Relative lowering of vapor pressure
Explanation:
Relative lowering of vapor pressure depends only on the mole fraction of the solute and is independent of temperature. Boiling point elevation, freezing point depression, and osmotic pressure are temperature-dependent.
99. What happens to the boiling point of a solvent when a non-volatile solute is added?
a) It increases
b) It decreases
c) It remains the same
d) It becomes equal to the freezing point
Answer: a) It increases
Explanation:
The addition of a non-volatile solute to a solvent increases the boiling point of the solution, a phenomenon known as boiling point elevation. This occurs because the presence of solute particles lowers the vapor pressure of the solution.
100. Which of the following explains the colligative property of freezing point depression?
a) Lowering of vapor pressure
b) Increase in solute-solvent interactions
c) Increase in boiling point
d) None of the above
Answer: a) Lowering of vapor pressure
Explanation:
Freezing point depression occurs because the addition of a solute lowers the vapor pressure of the solution, making it harder for the solvent to freeze. The temperature must be lowered further to reach the freezing point.
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