2) Evaporation and Polarity Lab -- PART I
(Lab Guidelines: 1,2,3,4,5&6[attach handout],8,10,12)
3) Purposes:
To use the relative rates of evaporation to differentiate between liquids which
possess varying degrees of molecular polarity.
To understand how molecular polarity affects the rate at which a substance will evaporate.
4) Introductory Information:
Review bond polarity and molecular polarity.
Complete the following statements in the Intro Section of your report:
A bond is polar if…
A bond is non-polar if…
A molecule is polar if…
A molecule is non-polar if…
Are my fingers really cold when I use fingernail polish remover??
5) Materials: 2-propanol (C3H8O), acetone (C3H6O), water, paper towels, rubber bands,
temperature probe.
6) Procedure:
1. Wrap paper towel around the end of a temperature probe, and secure with a rubber band.
2. Dip the probe into one of the three liquids to be tested. Do not remove it.
3. Press collect to begin collecting temperature data. Leave the probe in the liquid for a few seconds.
4. Now remove the probe from the liquid. The paper should be saturated with the liquid.
5. Allow computer to collect data for 150 seconds at which time the temperature should begin to level off.
Click the stop button. Store this run as shown in class.
6. Remove the paper. Throw it away. Retrieve the rubber band for re-use.
7. Allow the thermometer to come back to room temperature.
8. Repeat steps 1-7 for the other two liquids, using a new piece of filter paper each time.
7) Data: Computer will take care of this for you.
8) Graph: Use text annotation to label substances at the 150 second mark. Print out your graph with all three runs.
Title the graph as well!
10) Questions: Use complete sentences where appropriate.
1. Draw the Lewis Structure for each of the 3 liquids used today (see materials for formulas).
(Hint: in 2-propanol all 3 carbon atoms are sp3 hybridized [have 4 bonding domains];
in acetone the 2 “end” carbon atoms are sp3 hybridized [have 4 bonding domains],
while the 1 “center” carbon atom is sp2 hybridized [has 3 bonding domains].)
2. Which molecules have polar bonds?
3. Classify each molecule as polar or non-polar (this is a reference to molecular polarity, not bond polarity).
4. Rank these molecules from least polar to most polar.
5. Which substance absorbed heat from the thermometer at the highest rate?
6. Which substance absorbed heat from the thermometer at the slowest rate?
7. Which substance evaporated the fastest?
8. Which substance evaporated the slowest?
9. Rank the three substances from slowest evaporation rate to fastest evaporation rate
10. Explain what you notice about how molecular polarity and evaporation rate are related to one another?
11. Do your best to explain why this is the case.
12) Conclusion: Write an awesome conclusion which sums up the lab
(Note: You can combine conclusions for parts I and II together into one conclusion).
2) Evaporation and Polarity Lab -- PART II
(Lab Guidelines: 1,2,3,4,5&6[attach handout],8,10,12)
3) Purpose: To predict the relative evaporation rates of cyclohexane, ethanol, and methanol.
To test our predictions by observing the cooling curve of each.
4) Introduction:
Draw the Lewis Structure for each of the 3 liquids used today (see materials for formulas).
Make a prediction, by sketching cooling curves for each of these three substances,
showing the relative rates of evaporation for each.
5) Materials: cyclohexane (C6H12), ethanol (C2H5OH), methanol (CH3OH), paper towels, rubber bands,
temperature probe.
6) Procedure: Follow the same procedure from Part I for these 3 substances
7) Data: Computer will take care of this for you.
8) Graph: Annotate each substance as in Part I. Print out your graph with all three runs. Title it too.
10) Questions: Use complete sentences where appropriate.
1. Which molecules have polar bonds?
2. Classify each molecule as polar or non-polar (this is a reference to molecular polarity, not bond
polarity).
3. Rank these molecules from least polar to most polar.
4. Which substance absorbed heat from the thermometer at the highest rate?
5. Which substance absorbed heat from the thermometer at the slowest rate?
6. Which substance evaporated the fastest?
7. Which substance evaporated the slowest?
8. Rank the three substances from slowest evaporation rate to fastest evaporation rate
9. Did the results match your predictions? If not, then explain how the results differ from
your predictions.
10. Do your best to explain why you obtained the results you did.
11. Which of these three substances would have the highest boiling point? Lowest boiling point?
Explain how you know.
12) Conclusion: Write an awesome conclusion which sums up the lab.
(Note: You can combine conclusions for parts I and II together into one conclusion).
Write a conclusion which demonstrates that you understand what you did. How did you accomplish the purposes?
Remember, here is a great guide for writing your conclusion:
1) Restate the purpose
2) Summarize the procedure and data collection
3) Discuss any important principles / equations used
4) Explain the graphs and/or math
5) Report your results
Also, please include any other interesting information you would like to add.