Raoult's Law - Essential Concepts for Competitive Exams

Raoults Law

Q. For a solution containing 2 components A and B, if the mole fraction of A is 0.6, what is the vapor pressure of the solution if the vapor pressure of pure A is 100 mmHg?

A. 60 mmHg
B. 100 mmHg
C. 40 mmHg
D. 80 mmHg

Solution

According to Raoult's Law, the vapor pressure of the solution is P_A = X_A * P_A^0 = 0.6 * 100 mmHg = 60 mmHg.

Correct Answer: D — 80 mmHg

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Q. For a solution to obey Raoult's Law, the interactions between solute and solvent must be:

A. Stronger than those in the pure components.
B. Weaker than those in the pure components.
C. Similar to those in the pure components.
D. Non-existent.

Solution

For a solution to obey Raoult's Law, the interactions between solute and solvent must be similar to those in the pure components.

Correct Answer: C — Similar to those in the pure components.

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Q. For an ideal solution, if the mole fraction of the solvent is 0.75, what is the vapor pressure of the solution if the vapor pressure of the pure solvent is 100 mmHg?

A. 75 mmHg
B. 100 mmHg
C. 25 mmHg
D. 50 mmHg

Solution

According to Raoult's Law, the vapor pressure of the solution is 0.75 * 100 mmHg = 75 mmHg.

Correct Answer: A — 75 mmHg

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Q. If a solution has a vapor pressure of 80 mmHg and the pure solvent has a vapor pressure of 100 mmHg, what is the mole fraction of the solvent?

A. 0.8
B. 0.75
C. 0.6
D. 0.5

Solution

Using Raoult's Law, the mole fraction of the solvent can be calculated as 80 mmHg / 100 mmHg = 0.8, which corresponds to a mole fraction of 0.75 for the solvent.

Correct Answer: B — 0.75

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Q. If the mole fraction of a solute in a solution is 0.2, what is the mole fraction of the solvent?

A. 0.8
B. 0.2
C. 0.5
D. 0.6

Solution

Mole fraction of solvent = 1 - mole fraction of solute = 1 - 0.2 = 0.8.

Correct Answer: A — 0.8

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Q. If the mole fraction of a solvent in a solution is 0.75, what is the vapor pressure of the solvent if its pure vapor pressure is 100 mmHg?

A. 75 mmHg
B. 100 mmHg
C. 25 mmHg
D. 50 mmHg

Solution

According to Raoult's Law, the vapor pressure of the solvent in the solution is 0.75 * 100 mmHg = 75 mmHg.

Correct Answer: A — 75 mmHg

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Q. If the mole fraction of a solvent in a solution is 0.8, what is the mole fraction of the solute?

A. 0.2
B. 0.8
C. 0.5
D. 0.1

Solution

The mole fraction of the solute is 1 - X_solvent = 1 - 0.8 = 0.2.

Correct Answer: A — 0.2

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Q. If the mole fraction of solute in a solution is 0.2, what is the mole fraction of the solvent?

A. 0.8
B. 0.2
C. 0.5
D. 0.6

Solution

The mole fraction of the solvent is 1 - X_solute = 1 - 0.2 = 0.8.

Correct Answer: A — 0.8

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Q. If the vapor pressure of a pure solvent is 80 mmHg and a non-volatile solute is added, resulting in a vapor pressure of 60 mmHg, what is the mole fraction of the solvent in the solution?

A. 0.75
B. 0.50
C. 0.25
D. 0.80

Solution

Using Raoult's Law, P_solution = X_solvent * P_pure_solvent; 60 mmHg = X_solvent * 80 mmHg; X_solvent = 60/80 = 0.75.

Correct Answer: A — 0.75

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Q. If the vapor pressure of a solution is 80 mmHg and the vapor pressure of the pure solvent is 120 mmHg, what is the mole fraction of the solvent in the solution?

A. 0.67
B. 0.33
C. 0.50
D. 0.75

Solution

Using Raoult's Law, P_solution = X_solvent * P_solvent^0; 80 = X_solvent * 120; X_solvent = 80/120 = 0.67.

Correct Answer: A — 0.67

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Q. If the vapor pressure of pure solvent A is 100 mmHg, and the mole fraction of A in the solution is 0.5, what is the vapor pressure of the solution according to Raoult's Law?

A. 50 mmHg
B. 100 mmHg
C. 150 mmHg
D. 200 mmHg

Solution

According to Raoult's Law, P_solution = X_A * P_A^0 = 0.5 * 100 mmHg = 50 mmHg.

Correct Answer: A — 50 mmHg

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Q. If the vapor pressure of pure solvent A is 100 mmHg, and the mole fraction of A in the solution is 0.6, what is the vapor pressure of the solution according to Raoult's Law?

A. 60 mmHg
B. 100 mmHg
C. 40 mmHg
D. 80 mmHg

Solution

Using Raoult's Law, P_solution = X_A * P_A^0 = 0.6 * 100 mmHg = 60 mmHg.

Correct Answer: A — 60 mmHg

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Q. If the vapor pressure of pure solvent A is 100 mmHg, what is the vapor pressure of a solution containing 0.5 mole fraction of A?

A. 50 mmHg
B. 100 mmHg
C. 75 mmHg
D. 25 mmHg

Solution

According to Raoult's Law, the vapor pressure of the solution is 0.5 * 100 mmHg = 50 mmHg.

Correct Answer: A — 50 mmHg

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Q. If the vapor pressure of pure solvent is 120 mmHg, what will be the vapor pressure of a solution containing 0.2 moles of solute in 1 mole of solvent?

A. 100 mmHg
B. 110 mmHg
C. 120 mmHg
D. 80 mmHg

Solution

Using Raoult's Law, the vapor pressure of the solution is P_solution = P_solvent * X_solvent = 120 * (1/(1+0.2)) = 120 * (1/1.2) = 100 mmHg.

Correct Answer: B — 110 mmHg

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Q. If the vapor pressure of pure solvent is 80 mmHg and the mole fraction of the solvent in the solution is 0.75, what is the vapor pressure of the solution?

A. 60 mmHg
B. 80 mmHg
C. 75 mmHg
D. 20 mmHg

Solution

Using Raoult's Law, P_solution = X_solvent * P_solvent^0 = 0.75 * 80 mmHg = 60 mmHg.

Correct Answer: A — 60 mmHg

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Q. In a binary solution of A and B, if component A has a higher vapor pressure than component B, what can be inferred about the solution?

A. It will show positive deviation from Raoult's Law.
B. It will show negative deviation from Raoult's Law.
C. It will have a lower boiling point than pure A.
D. It will have a higher boiling point than pure B.

Solution

If component A has a higher vapor pressure than component B, the solution will show positive deviation from Raoult's Law.

Correct Answer: A — It will show positive deviation from Raoult's Law.

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Q. In a binary solution of A and B, if the mole fraction of A is 0.6, what is the mole fraction of B?

A. 0.4
B. 0.6
C. 1.0
D. 0.2

Solution

The mole fraction of B can be calculated as 1 - mole fraction of A = 1 - 0.6 = 0.4.

Correct Answer: A — 0.4

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Q. In a binary solution of A and B, if the vapor pressure of A is 80 mmHg and that of B is 40 mmHg, what is the total vapor pressure when both are present?

A. 40 mmHg
B. 80 mmHg
C. 120 mmHg
D. 100 mmHg

Solution

The total vapor pressure is the sum of the partial pressures: P_total = P_A + P_B = 80 mmHg + 40 mmHg = 120 mmHg.

Correct Answer: D — 100 mmHg

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Q. In a binary solution of A and B, if the vapor pressure of A is 80 mmHg and that of B is 40 mmHg, what is the total vapor pressure of the solution if the mole fraction of A is 0.75?

A. 60 mmHg
B. 70 mmHg
C. 80 mmHg
D. 90 mmHg

Solution

Total vapor pressure = P_A + P_B = (0.75 * 80) + (0.25 * 40) = 60 + 10 = 70 mmHg.

Correct Answer: D — 90 mmHg

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Q. In a binary solution of A and B, if the vapor pressure of pure A is 150 mmHg and pure B is 50 mmHg, what is the total vapor pressure when the mole fraction of A is 0.4?

A. 90 mmHg
B. 120 mmHg
C. 150 mmHg
D. 100 mmHg

Solution

Total vapor pressure = (X_A * P_A^0) + (X_B * P_B^0) = (0.4 * 150) + (0.6 * 50) = 60 + 30 = 90 mmHg.

Correct Answer: B — 120 mmHg

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Q. In a binary solution of A and B, if the vapor pressure of pure A is 80 mmHg and that of pure B is 40 mmHg, what is the vapor pressure of the solution if the mole fraction of A is 0.6?

A. 64 mmHg
B. 72 mmHg
C. 80 mmHg
D. 56 mmHg

Solution

Using Raoult's Law, the vapor pressure of the solution = (0.6 * 80 mmHg) + (0.4 * 40 mmHg) = 64 mmHg.

Correct Answer: B — 72 mmHg

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Q. In a binary solution of A and B, if the vapor pressure of pure A is 80 mmHg and pure B is 40 mmHg, what is the vapor pressure of the solution if the mole fraction of A is 0.6?

A. 64 mmHg
B. 72 mmHg
C. 80 mmHg
D. 56 mmHg

Solution

Using Raoult's Law, the vapor pressure of the solution = (0.6 * 80 mmHg) + (0.4 * 40 mmHg) = 64 mmHg.

Correct Answer: B — 72 mmHg

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Q. In a binary solution of A and B, if the vapor pressure of pure A is 80 mmHg and pure B is 40 mmHg, what is the vapor pressure of component A if the mole fraction of A is 0.6?

A. 48 mmHg
B. 64 mmHg
C. 80 mmHg
D. 32 mmHg

Solution

Using Raoult's Law, the vapor pressure of A in the solution is 0.6 * 80 mmHg = 48 mmHg.

Correct Answer: B — 64 mmHg

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Q. In a binary solution of A and B, if the vapor pressure of pure A is 80 mmHg and that of pure B is 40 mmHg, what is the total vapor pressure when the mole fraction of A is 0.6?

A. 64 mmHg
B. 72 mmHg
C. 80 mmHg
D. 88 mmHg

Solution

Using Raoult's Law, the total vapor pressure = (0.6 * 80 mmHg) + (0.4 * 40 mmHg) = 48 mmHg + 16 mmHg = 64 mmHg.

Correct Answer: B — 72 mmHg

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Q. In a binary solution of A and B, if the vapor pressure of pure A is 80 mmHg and pure B is 40 mmHg, what is the total vapor pressure when the mole fraction of A is 0.5?

A. 60 mmHg
B. 70 mmHg
C. 80 mmHg
D. 50 mmHg

Solution

Total vapor pressure = P_A + P_B = (0.5 * 80) + (0.5 * 40) = 40 + 20 = 60 mmHg.

Correct Answer: B — 70 mmHg

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Q. In a solution of 1 mol of solute in 9 mol of solvent, what is the mole fraction of the solute?

A. 0.1
B. 0.2
C. 0.5
D. 0.9

Solution

Mole fraction of solute = moles of solute / (moles of solute + moles of solvent) = 1 / (1 + 9) = 0.1.

Correct Answer: A — 0.1

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Q. In a solution of 1 mole of solute B in 3 moles of solvent A, what is the mole fraction of solvent A?

A. 0.25
B. 0.75
C. 0.33
D. 0.67

Solution

Mole fraction of A = moles of A / (moles of A + moles of B) = 3 / (3 + 1) = 0.75.

Correct Answer: B — 0.75

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Q. In a solution of a non-volatile solute, how does the addition of solute affect the boiling point of the solvent?

A. It decreases the boiling point
B. It has no effect on the boiling point
C. It increases the boiling point
D. It depends on the nature of the solute

Solution

The addition of a non-volatile solute raises the boiling point of the solvent, a phenomenon known as boiling point elevation.

Correct Answer: C — It increases the boiling point

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Q. In a solution of a non-volatile solute, how does the vapor pressure compare to that of the pure solvent?

A. Higher than the pure solvent
B. Lower than the pure solvent
C. Equal to the pure solvent
D. Depends on the temperature

Solution

The presence of a non-volatile solute lowers the vapor pressure of the solvent compared to that of the pure solvent.

Correct Answer: B — Lower than the pure solvent

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Q. In a solution of two volatile components A and B, if the mole fraction of A is 0.6, what is the vapor pressure of the solution if the vapor pressure of pure A is 100 mmHg and that of pure B is 50 mmHg?

A. 80 mmHg
B. 90 mmHg
C. 70 mmHg
D. 60 mmHg

Solution

Using Raoult's Law, the vapor pressure of the solution is P_total = (0.6 * 100) + (0.4 * 50) = 60 + 20 = 80 mmHg.

Correct Answer: B — 90 mmHg

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Raoults Law

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