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.
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