Last modified: Wed 12/31/1969 06:00:00 pm
BCE

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Answer all of the questions below. If you do not know an answer enter CNA. However, it will help me the most if you answer each question with your best intuition/idea about what would be a reasonable answer.

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Consider the sketches of four barometers (above).  Barometer i) shows the measurement of atmospheric pressure which is equivalent to the height the column of mercury is sustained (in this case atmospheric pressure is 760 mm Hg).  Barometer ii) depicts the situation of a sample of water having been injected into the tube.  Barometer iii) and iv) depict samples of diethyl ether having been injected into the tubes.  All four barometers are at the same temperature.

1. Briefly describe/define vapor pressure for a liquid. (Check pages 425 and 426 in your textbook.)

2. In barometer i) no liquid has been injected, so only mercury is present. Since the vapor pressure of mercury at 25 degrees Celsius is very low, it is assumed the small volume of space above the mercury liquid contains very few particles. In Barometer ii, a sample of water has been injected, why is the height of the mercury column lower in Barometer ii compared to Barometer i?

3. In the Figure above, what is the equilibrium vapor pressure of water?

mmHg

4. In the Figure above, what is the equilibrium vapor pressure of diethyl ether?

mmHg

5. What would explain the height of the mercury column in Barometer iv? NOTE: A smaller sample of diethyl ether was injected into barometer iv compared to barometer iii.

In the above figure is a plot of vapor pressure versus temperature for three liquids;

diethyl ether (red data points)

ethyl alcohol (blue data points)

water (black data points)

Using the graph answer the following questions;

6. Which liquid (diethyl ether, ethyl alcohol or water) has the highest vapor pressure at 25 °C?

7a. What is the normal boiling point of water?

°C

b) What is the normal boiling point of diethyl ether?

°C

8. Which substance has the strongest intermolecular attractive forces?

Briefly explain your answer.

9a. Using the plot above, what is the vapor pressure of water at 20 °C?

mmHg

b) Using the plot above, what is the vapor pressure of water at 40 °C?

mmHg

10. When you heat a sample of water, why does the vapor pressure increase?

11. Is there anything about the questions that you feel you do not understand? List your concerns/questions.

12. If there is one question you would like to have answered in lecture, what would that question be?