Lab Evaporation and Intermolecular Attraction



Lab Evaporation and Intermolecular Attraction

*This lab will be submitted electronically through google classroom. (Times New Roman, size 12, normal margins) You will also need to print a copy and turn it in! (Procrastination on your part does not constitute an emergency on my part. Plan ahead, I am not printing your lab for you and you are not leaving class to print it.) You will be able to copy and paste the following sections from the lab documents on the website: purpose, background, materials, safety, procedure, data table.

Purpose: Investigate the relationship of dispersion forces and hydrogen bonding forces in intermolecular attractions.

Background: In this experiment, temperature probes covered with filter paper are placed in various liquids. Evaporation occurs when the probe is removed from the liquid's container (see figure 1). This evaporation is an endothermic process that results in a temperature decrease. The magnitude of a temperature decrease is, like viscosity and boiling temperature, related to the strength of intermolecular forces of attraction. In this experiment, you will study temperature changes caused by the evaporation of several liquids and relate the temperature changes to the strength of intermolecular forces of attraction. The temperature change is greater if more evaporation occurs (weaker intermolecular forces). You will use the results to predict, and then measure, the temperature change for several other liquids.

You will encounter two types of organic compounds in this experiment — alkanes and alcohols. The two alkanes are pentane, C5H12, and hexane, C6H14. In addition to carbon and hydrogen atoms, alcohols also contain the -OH functional group. Methanol, CH3OH, and ethanol, C2H5OH, are two of the alcohols that we will use in this experiment. You will examine the molecular structure of alkanes and alcohols for the presence and relative strength of two intermolecular forces—hydrogen bonding and dispersion forces. Dispersion forces exist between any two molecules and generally increase as the molecular weight of the molecule increases. A hydrogen bond can occur when, in one molecule, a hydrogen atom is bonded directly to an N, O, or F atom (the donor) and that hydrogen is attracted to a lone pair on an N, O, or F atom in another molecule (the acceptor). Both a donor and an acceptor must be present for a hydrogen bond to occur.

Materials: ethanol, 1-propanol, 1-ethanol, pentane, methanol, hexane, test tubes, temperature probes, filter paper, rubber bands, Vernier platform & computer

Safety Warning:

The chemicals used in this experiment are flammable and poisonous. Avoid inhaling their vapors. Avoid contacting them with your skin or clothing. Be sure there are no open flames in the lab during the experiment. Notify your teacher immediately if an accident occurs.

Procedure:

1. Setup the Vernier platform and computer.

• Plug temperature probes into channels 1 and 2 on the Vernier Platform.

• Using the search icon in the bottom left corner, search for logger pro.

• Go to “Experiment”, “Extend Collection” to 270 seconds.

• Click on the temp 1 title box and change it to “ethanol temp”. Click on the temp 2 title box and change it to “1-propanol” temp”.

*You will need to change the temp title boxes each time you go to a new set of solutions.

2. Wrap probes 1 and 2 with ¼ pieces of filter paper and secure them with a paper clip.

3. Keep the stoppers on the test tubes to prevent evaporation. Only remove stoppers when you are ready to use the solution.

4. Position probe 1 in an upright manner in the ethanol test tube. Position probe 2 in the 1-propanol test tube in the same way.

5. After the probes have been in the liquids for at least 45 seconds, click the green arrow to “begin collecting” data. Monitor the temperature for 15 seconds then simultaneously remove the probes from the liquid and place them so the probe tips extend approximatelyt 5cm over the edge of the table. Set a textbook on top of the probes (black part) to keep them in place.

6. When data collection is complete, go to “Analyze”, “Statistics”, and check both boxes. You should now be able to view the minimum and maximum temperatures for each sample. Record these in the data table. View and record the change in temperature in the data table.

7. Wearing gloves, dispose of the filter paper (unfolded) and the paper clip in the buckets located in the fume hood.

8. Wipe the probes with a paper towel.

9. Predict the line for 1-octanol. Go to “analyze”, “draw prediction” and draw the predicted line for 1-octanol. Label it using the “insert”, “text”.

*After the next pair of solutions “1-octanol” and “pentane”, predict the line for hexane. Using the tools in logger pro, add this to your graph and label it “hexane”.

10. Save your data. All group members will need to have access to the data.

11. Repeat steps 1-10 for the other pairs of liquids.

Data

|Substance |Maximum temperature (oC) |Minimum temperature (oC) |∆T (oC) |

|ethanol | | | |

|1-propanol | | | |

|1-octanol | | | |

|pentane | | | |

|methanol | | | |

|hexane | | | |

*NOTE: no calculations for this lab

Discussion Questions: Answer these in complete sentences in the “discussion” section of your lab report.

1. The change in temperature tells you about how readily a sample evaporates. Choose the appropriate response to each statement below.

|Large ∆T values mean that the sample |DOES |DOES NOT |evaporate readily. |

| | | | |

|Small ∆T values mean that the sample |DOES |DOES NOT |evaporate readily. |

2. Correlate your answers to how readily a sample evaporates to the strength of the intermolecular forces in that molecule. Choose the appropriate response to complete the statement.

If the sample evaporates readily, then the relative strength of the IMFs in the molecule is:

STRONG WEAK

If the sample does not evaporate, then the relative strength of the IMFs in the molecule is: STRONG WEAK

3. Two liquids, an alkane and an alcohol, have similar molecular weights but significantly different ΔT values. Explain the difference in the ΔT values based on their intermolecular forces.

4. Which of the alkanes from the lab has the strongest intermolecular forces of attraction? Explain using the results of your experiment.

Graph

Include your graphs (3) from logger pro.

Using excel or google sheets, create a graph (graph 4) for the four alcohols. Graph (T values versus molecular weight. Plot molecular weight on the horizontal axis and (T on the vertical axis. Identify each alcohol on the graph. Add the answer to this question, in a complete sentence, to the graph. “What is the relationship between mass and intermolecular force?”

Conclusion- See lab report guidelines and rubric for requirements.

*Error analysis is NOT part of your lab report. We will do a group error analysis in class.

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