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.
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