Here below some basic MCQ’s about “Raoult’s law and colligative properties” with answer which is well explained. Let’s check one by one.
1. Raoult’s law is applicable to which type of solutions?
A. Ideal solutions
B. Non-ideal solutions
C. Dilute solutions only
D. Colloidal solutions
Answer: A. Ideal solutions
Explanation:
Raoult’s Law states that the vapor pressure of a volatile component in a solution is directly proportional to its mole fraction. This law is strictly applicable to ideal solutions, where the interactions between solute-solute, solvent-solvent, and solute-solvent molecules are similar.
2. Colligative properties depend on:
A. Nature of solute
B. Type of solvent
C. Number of solute particles
D. Pressure of the system
Answer: C. Number of solute particles
Explanation:
Colligative properties (like boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure) depend only on the number of solute particles in a solution, not on their nature or type. These properties arise because the addition of solute particles disrupts the physical properties of the solvent.
3. Which of the following is NOT a colligative property?
A. Vapor pressure lowering
B. Boiling point elevation
C. Osmotic pressure
D. Surface tension
Answer: D. Surface tension
Explanation:
Colligative properties include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. Surface tension is a physical property that depends on the nature of the solvent and is not a colligative property.
4. According to Raoult’s Law, the relative lowering of vapor pressure is equal to:
A. The mole fraction of the solute
B. The mole fraction of the solvent
C. The number of solute particles
D. The total pressure of the system
Answer: A. The mole fraction of the solute
Explanation:
Raoult’s Law states that the relative lowering of vapor pressure of a solvent in a solution is directly proportional to the mole fraction of the solute. The equation is:
Relative lowering of vapor pressure=ΔPP0=xsoluteRelative lowering of vapor pressure=P0ΔP=xsolute
Where xsolutexsolute is the mole fraction of the solute.
5. Which colligative property can be used to determine molar mass of a solute?
A. Vapor pressure lowering
B. Surface tension
C. Boiling point elevation
D. Refractive index
Answer: C. Boiling point elevation
Explanation:
Boiling point elevation can be used to determine the molar mass of a solute. When a non-volatile solute is added to a solvent, the boiling point of the solution increases. This elevation is related to the molal concentration of the solute, which can be used to calculate its molar mass.
6. What happens to the freezing point of a solution when a solute is added to a solvent?
A. It increases
B. It decreases
C. It remains unchanged
D. It depends on the type of solute
Answer: B. It decreases
Explanation:
When a non-volatile solute is added to a solvent, the freezing point of the solution decreases. This is known as freezing point depression, a colligative property. The presence of solute particles interferes with the crystallization process of the solvent, lowering its freezing point.
7. Which statement about osmotic pressure is true?
A. It decreases with an increase in solute concentration
B. It is not affected by temperature
C. It is a colligative property
D. It is always zero in ideal solutions
Answer: C. It is a colligative property
Explanation:
Osmotic pressure is a colligative property because it depends on the number of solute particles in a solution. It increases with an increase in solute concentration and is directly proportional to temperature.
8. In an ideal solution, the total vapor pressure is:
A. Lower than predicted by Raoult’s Law
B. Higher than predicted by Raoult’s Law
C. Equal to the sum of the partial vapor pressures
D. Independent of the composition
Answer: C. Equal to the sum of the partial vapor pressures
Explanation:
In an ideal solution, the total vapor pressure is equal to the sum of the partial vapor pressures of the components, as described by Raoult’s Law. Each component’s partial vapor pressure is proportional to its mole fraction in the solution.
9. Which of the following statements is true regarding an ideal solution?
A. The enthalpy of mixing is zero
B. There is a large volume change during mixing
C. Raoult’s law is not applicable
D. The solution forms only at low temperatures
Answer: A. The enthalpy of mixing is zero
Explanation:
For an ideal solution, the enthalpy of mixing is zero, meaning no heat is absorbed or evolved during the mixing process. Additionally, the volume of the solution is the sum of the volumes of the components, with no expansion or contraction.
10. The depression in freezing point is proportional to:
A. The molality of the solution
B. The molarity of the solution
C. The mole fraction of the solute
D. The volume of the solution
Answer: A. The molality of the solution
Explanation:
The depression in freezing point is directly proportional to the molality (moles of solute per kilogram of solvent) of the solution. This is expressed as:
ΔTf=Kf⋅m
Where KfKf is the cryoscopic constant and mm is the molality.
Leave a comment