Q: In a two-component ideal solution at constant temperature, the total vapor pressure is given by which equation?

$$p_{\text{tot}} = x_A p_A^* + x_B p_B^*$$

Q: If the mole fraction of component B in the liquid phase is $$x_B = 0.6$$, $$p_B^* = 80$$ Torr, and $$p_C^* = 40$$ Torr, what is the partial pressure of B in the vapor above the solution according to Raoult's Law?

$$p_B = x_B p_B^* = 0.6 \times 80 = 48$$ Torr

Question 1

Which law describes the relationship between the partial pressure of a component in an ideal solution and its mole fraction in the liquid phase?

Accepted Answer

Raoult's Law

Question 2

In a two-component ideal solution at constant temperature, the total vapor pressure is given by which equation?

Accepted Answer

$$p_{	ext{tot}} = x_A p_A^* + x_B p_B^*$$

Question 3

A mixture of 5.00 mol benzene and 3.25 mol toluene is prepared. At 298 K, $$p^*_{	ext{benzene}} = 96.4$$ Torr and $$p^*_{	ext{toluene}} = 28.9$$ Torr. What is the total vapor pressure when the vapor phase first appears?

Accepted Answer

$$69.8$$ Torr

Question 4

Which of the following best describes an azeotrope?

Accepted Answer

A mixture that cannot be separated into its components by simple distillation

Question 5

In a vapor-liquid equilibrium diagram for an ideal binary mixture, what does the area between the two curves represent?

Accepted Answer

The region where both liquid and vapor phases coexist

Question 6

If the mole fraction of component B in the liquid phase is $$x_B = 0.6$$, $$p_B^* = 80$$ Torr, and $$p_C^* = 40$$ Torr, what is the partial pressure of B in the vapor above the solution according to Raoult's Law?

Accepted Answer

$$p_B = x_B p_B^* = 0.6 	imes 80 = 48$$ Torr

Question 7

Which of the following statements about fractional distillation is correct?

Accepted Answer

Each condensation and vaporization step increases the concentration of the more volatile component in the vapor phase

Question 8

In the lever rule, what does the ratio $$\frac{l_\beta}{l_\alpha}$$ represent in a two-phase region?

Accepted Answer

The ratio of the lengths of the tie line segments from the overall composition to the phase boundaries

Question 9

Which of the following is a real-world application of vapor-liquid equilibrium and distillation?

Accepted Answer

Separation of crude oil into gasoline, kerosene, and diesel in a refinery

Question 10

A solution of ethanol and water forms an azeotrope at 78.2°C. What does this mean for the distillation of ethanol from water?

Accepted Answer

It is impossible to obtain pure ethanol by simple fractional distillation

Question 11

Given a binary mixture at constant pressure, which curve on a temperature-composition diagram represents the boiling point of the liquid?

Accepted Answer

The lower curve

Question 12

Which of the following best explains why the composition of the vapor phase is different from the liquid phase in an ideal solution?

Accepted Answer

The more volatile component has a higher tendency to escape into the vapor phase

Question 13

A mixture of chloroform and methanol forms a low-boiling azeotrope. What is a characteristic of this system?

Accepted Answer

The mixture boils at a temperature lower than either pure component

Question 14

If $$x_B = 0.4$$, $$p_B^* = 100$$ Torr, $$x_C = 0.6$$, $$p_C^* = 50$$ Torr, what is the total vapor pressure above the solution?

Accepted Answer

$$p_{	ext{tot}} = 0.4 	imes 100 + 0.6 	imes 50 = 70$$ Torr

Question 15

Which of the following is NOT a region found in a typical vapor-liquid phase diagram for a binary mixture?

Accepted Answer

Solid only

Question 16

In the context of industrial distillation columns, what is the main purpose of having multiple trays or plates?

Accepted Answer

To allow repeated vaporization and condensation, enriching the more volatile component at each stage

Question 17

Which equation correctly expresses Dalton's Law for a binary vapor mixture?

Accepted Answer

$$p_{	ext{tot}} = p_A + p_B$$

Question 18

A student claims that the lever rule can be used to determine the relative amounts of phases in a two-phase region of a phase diagram. Is this correct?

Accepted Answer

Yes, the lever rule gives the relative amounts of each phase present

Question 19

Which of the following mixtures forms a high-boiling azeotrope?

Accepted Answer

Water and formic acid

Phase Diagrams and Liquid-Vapour Equilibria in Two-Component Systems

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