Q: If the boiling point of a liquid at 760 mm Hg is 150°C, what would be its approximate boiling point at 10 mm Hg, assuming a drop of 0.5°C for each 10 mm Hg decrease in pressure?

$$125$$°C$$ - (75 \times 0.5)$$°C $$= 112.5$$°C

Question 1

Which of the following statements best describes the principle behind fractional distillation?

Accepted Answer

It separates liquids whose boiling point difference is less than 100°C by repeated vaporization-condensation cycles.

Question 2

A mixture of ethanol and water is distilled. At a certain composition, the mixture boils at a constant temperature and the vapor has the same composition as the liquid. What is this phenomenon called?

Accepted Answer

Azeotrope

Question 3

According to Raoult’s Law, what is the partial vapor pressure of component A in a solution if the mole fraction of A is $$N_A = 0.4$$ and the vapor pressure of pure A is $$P_A^0$ = 800 mm Hg$$?

Accepted Answer

$$P_A = 320 mm Hg$$

Question 4

Which type of distillation is most appropriate for purifying a liquid that decomposes at its normal boiling point above 200°C?

Accepted Answer

Vacuum distillation

Question 5

During a simple distillation of a mixture of two liquids with very similar boiling points, what is the expected outcome?

Accepted Answer

Poor separation; the distillate will contain significant amounts of both components.

Question 6

A solution contains 0.5 mole fraction of A and 0.5 mole fraction of B. The vapor pressure of pure A is 1020 mm Hg and pure B is 500 mm Hg. What is the total vapor pressure above the solution according to Raoult’s Law?

Accepted Answer

$$760 mm Hg$$

Question 7

Which of the following best explains why it is impossible to obtain pure ethanol by distillation of an ethanol-water mixture?

Accepted Answer

Ethanol and water form a minimum boiling point azeotrope.

Question 8

In a fractional distillation column, what does the term 'theoretical plate' refer to?

Accepted Answer

A single vaporization-condensation cycle equivalent to one simple distillation.

Question 9

If the boiling point of a liquid at 760 mm Hg is 150°C, what would be its approximate boiling point at 10 mm Hg, assuming a drop of 0.5°C for each 10 mm Hg decrease in pressure?

Accepted Answer

$$125$$°C$$ - (75 	imes 0.5)$$°C $$= 112.5$$°C

Question 10

Which of the following is a correct application of Dalton’s Law in the context of distillation?

Accepted Answer

The total vapor pressure above a solution is the sum of the partial vapor pressures of each component.

Question 11

A mixture of benzene and toluene is distilled. The first distillate is enriched in benzene. What is the best way to obtain nearly pure benzene from this mixture?

Accepted Answer

Redistill the first distillate and collect the initial fraction.

Question 12

Which of the following statements about azeotropes is FALSE?

Accepted Answer

Azeotropes always have a boiling point between those of the pure components.

Question 13

In the Fischer esterification reaction, why is azeotropic distillation often used?

Accepted Answer

To remove water and drive the reaction toward ester formation.

Question 14

Which of the following best describes the behavior of a maximum boiling point azeotrope?

Accepted Answer

The azeotrope boils at a temperature higher than either pure component.

Question 15

What is the effect of increasing the number of theoretical plates in a fractional distillation column?

Accepted Answer

It increases the efficiency and purity of the separated components.

Question 16

A solution at 100°C contains 0.5 mole fraction of A and 0.5 mole fraction of B. The vapor pressure of pure A is 1020 mm Hg and pure B is 500 mm Hg. What is the mole fraction of A in the vapor phase at the boiling point?

Accepted Answer

$$0.67$$

Question 17

Which of the following is a key advantage of using a diaphragm vacuum pump over a mechanical vacuum pump in organic distillation?

Accepted Answer

It avoids contamination by oil and is more solvent-friendly.

Question 18

In a distillation experiment, why is it important to record both temperature and volume of distillate at regular intervals?

Accepted Answer

To monitor the progress of separation and identify the composition of the distillate.

Question 19

Which of the following statements about steam distillation is correct?

Accepted Answer

It is used to distill substances that decompose at their boiling points and are immiscible with water.

Distillation in Organic Chemistry: Principles, Methods, and Applications

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