21. The colligative property that is most useful for determining the molar mass of polymers is:
A. Osmotic pressure
B. Boiling point elevation
C. Freezing point depression
D. Vapor pressure lowering
Answer: A. Osmotic pressure
Explanation:
Osmotic pressure is particularly useful in determining the molar mass of polymers because it is more sensitive for solutions with large molar masses, like polymers, where small changes in concentration affect the osmotic pressure significantly.
22. The relative lowering of vapor pressure of a solvent is equal to:
A. Mole fraction of solute
B. Mole fraction of solvent
C. Molality of solution
D. Molarity of solution
Answer: A. Mole fraction of solute
Explanation:
Raoult’s law states that the relative lowering of vapor pressure is directly proportional to the mole fraction of the solute in the solution.
23. A solution that shows positive deviation from Raoult’s law will have:
A. Strong solute-solvent interactions
B. Weak solute-solvent interactions
C. No interactions between solute and solvent
D. Equal solute-solvent and solvent-solvent interactions
Answer: B. Weak solute-solvent interactions
Explanation:
A solution that shows positive deviation from Raoult’s law has weaker solute-solvent interactions than solvent-solvent or solute-solute interactions, resulting in a higher vapor pressure than expected.
24. Colligative properties are applicable to which type of solutes?
A. Non-electrolytes only
B. Electrolytes only
C. Both electrolytes and non-electrolytes
D. Colloidal solutions
Answer: C. Both electrolytes and non-electrolytes
Explanation:
Colligative properties apply to both electrolytes and non-electrolytes, as they depend on the number of solute particles, whether they are molecules (non-electrolytes) or ions (electrolytes).
25. In an aqueous solution, the freezing point is lowered by 1.86°C when 1 mol of solute is dissolved in 1 kg of water. This constant is called:
A. Freezing point depression constant
B. Boiling point elevation constant
C. Osmotic constant
D. Van’t Hoff factor
Answer: A. Freezing point depression constant
Explanation:
The constant that represents the freezing point depression per molal concentration of a solute in a solvent is called the freezing point depression constant (K_f). For water, it is approximately 1.86°C·kg/mol.
26. Raoult’s law is applicable only to:
A. Electrolytic solutions
B. Nonelectrolytic solutions
C. Both electrolytic and nonelectrolytic solutions
D. Ideal solutions
Answer: D. Ideal solutions
Explanation:
Raoult’s law is strictly applicable to ideal solutions, where solute-solvent, solvent-solvent, and solute-solute interactions are similar. Non-ideal solutions show deviations from Raoult’s law.
27. Which of the following is not affected by the presence of a solute in a solution?
A. Freezing point
B. Boiling point
C. Vapour pressure
D. Density
Answer: D. Density
Explanation:
Colligative properties such as freezing point, boiling point, and vapor pressure are affected by the presence of a solute, whereas density is not directly a colligative property.
28. When a non-volatile solute is added to a volatile solvent, the vapor pressure of the solution:
A. Increases
B. Decreases
C. Remains the same
D. First increases, then decreases
Answer: B. Decreases
Explanation:
The addition of a non-volatile solute to a volatile solvent lowers the vapor pressure of the solvent. This happens because the solute particles occupy some of the surface area, reducing the number of solvent molecules that can escape into the vapor phase.
29. Which of the following is a colligative property?
A. Refractive index
B. Surface tension
C. Osmotic pressure
D. Viscosity
Answer: C. Osmotic pressure
Explanation:
Osmotic pressure is a colligative property, which depends only on the number of solute particles in a solution and not on their nature.
30. The colligative property used in desalination of water by reverse osmosis is:
A. Freezing point depression
B. Boiling point elevation
C. Vapor pressure lowering
D. Osmotic pressure
Answer: D. Osmotic pressure
Explanation:
Osmotic pressure is utilized in the process of reverse osmosis to desalinate water. By applying pressure greater than the osmotic pressure, pure water is forced through a semi-permeable membrane, leaving the solutes behind.
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