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LAB in Observations, Physical Properties, Mixtures, Solubility, Intermolecular Forces, Polarity, Identifying an Unknown, Intermolecular Forces, Chemical Properties, Intramolecular Forces, Mixtures. Last updated January 27, 2021.

Summary

In this lesson, students determine whether unknown substances are polar, nonpolar, or ionic by testing their solubilities.

Grade Level

High school

Objectives

By the end of this lesson, students should be able to

Use known solutions to determine whether an unknown is polar, nonpolar, or ionic.
Exhibit their understanding of the differences between polar, nonpolar, and ionic substances.
Apply their understanding of “like dissolves like.”
Recognize how intermolecular forces can help identify intramolecular forces within a compound.

Chemistry Topics

This lesson supports students’ understanding of

Solubility
Polarity
Intermolecular forces
Intramolecular forces

Time

Teacher Preparation: 45 minutes

Lesson: one class period

Materials

Distilled water
95% isopropyl alcohol
Vegetable oil
Iodine – Compound A
Naphthalene – Compound B
Sodium chloride – Compound C
Acetic acid (vinegar) – Solution A
Ethanol – Solution B
Acetone – Solution C
Test tubes
Test tube rack
Stirring rods

Safety

Always wear safety goggles when handling chemicals in the lab.
Students should wash their hands thoroughly before leaving the lab.
When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

Suggested unknowns for solids and solutions are given in the materials section. Do not tell students the identity of these substances until after they’ve completed the investigation. They should figure out using what they know about solubility and intramolecular forces what type of compound each sample is.
The substances are as follows:

Water	Polar
Isopropyl alcohol	Polar
Vegetable oil	Nonpolar
Acetic acid	Polar
Ethanol	Polar (with a nonpolar portion)
Acetone	Nonpolar (with a polarizable portion)
Iodine	Nonpolar
Naphthalene	Nonpolar
Sodium chloride	Ionic

All possible combinations and expected results:

Water	Isopropyl alcohol	Soluble
Water	Vegetable oil	Insoluble
Water	Acetic acid	Soluble
Water	Ethanol	Soluble
Water	Acetone	Soluble – probably an unexpected result. The water encourages the dipole in acetone.
Water	Iodine	Insoluble
Water	Naphthalene	Insoluble
Water	Sodium chloride	Soluble
Isopropyl alcohol	Vegetable oil	Insoluble
Isopropyl alcohol	Acetic acid	Soluble (if you add H₂SO₄ as a catalyst, they react and form isopropyl acetate, which smells fruity)
Isopropyl alcohol	Ethanol	Soluble
Isopropyl alcohol	Acetone	Soluble
Isopropyl alcohol	Iodine	Soluble
Isopropyl alcohol	Naphthalene	Insoluble
Isopropyl alcohol	Sodium chloride	Insoluble
Vegetable oil	Acetic acid	Insoluble
Vegetable oil	Ethanol	Insoluble
Vegetable oil	Acetone	Soluble –in oil, the nonpolar properties of acetone allow for it to be soluble.
Vegetable oil	Iodine	Soluble
Vegetable oil	Naphthalene	Soluble
Vegetable oil	Sodium chloride	Insoluble
Acetic acid	Ethanol	Soluble
Acetic acid	Acetone	Insoluble
Acetic acid	Iodine	Insoluble
Acetic acid	Naphthalene	Insoluble
Acetic acid	Sodium chloride	Soluble
Ethanol	Acetone	Insoluble
Ethanol	Iodine	Soluble (unexpected – the I₂ interacts with the nonpolar portion of ethanol)
Ethanol	Naphthalene	Insoluble
Ethanol	Sodium chloride	Soluble
Acetone	Iodine	Soluble
Acetone	Naphthalene	Soluble
Acetone	Sodium chloride	Insoluble

For the Student

Lesson

Prelab Questions

You’ve been investigating intermolecular forces in a variety of ways so far. This activity will help you better understand how polarity relates to this idea. Here are some questions to consider. Don’t answer them individually; craft a paragraph that discusses these ideas. If there are other aspects of intermolecular forces that you’d like to include, please do.

What are the differences between physical and chemical properties?
Are there any connections between intermolecular and intramolecular forces? Explain.
Explain whether intermolecular or intramolecular forces are more important when determining whether two compounds will be soluble in each other.
When a compound of your choice is put in water, draw a picture describing why they are soluble with each other. Label any forces (intra and inter).
When oil and vinegar are mixed, explain why they separate. You can draw a picture to help with your explanation if you would like.
At room temperature, would you expect a polar, nonpolar, or ionic substance to be solid? Why? How about liquid? Why?

Problem

What affects physical properties? How can physical properties help predict solubility?

Procedure & Data

You have to come up with some rules for solubility without knowing the chemical makeup of various substances. Come up with a list of trials to conduct. You will carry out seven test trials. Before mixing, predict the outcome. Carry out each experiment observing carefully, so you can accurately record the data.

Substances to test for solubility: Water, Isopropyl alcohol, Vegetable oil, Compound A, Compound B

Substances (test trials)	Predict	Actual

Using your data, determine whether each substance is polar, nonpolar, or ionic.

Substance	Polar, nonpolar, ionic
Water
Isopropyl alcohol
Vegetable oil
Compound A
Compound B
Compound C
Solution A
Solution B
Solution C

If you need more data to support your conclusions, come up with two more tests to help you obtain enough data. Follow the same procedure for mixing and taking observations.

Substances (extra trials)	Predict	Actual

Analysis

Pick three other combinations of compounds you did not test – determine if they would be soluble or insoluble with each other. Explain how you made each prediction.
Explain your thought process of how you determined the properties of your unknown compounds and your unknown solutions. Did you consider only the intermolecular forces, or did intramolecular forces play a part in determining their properties?
Were any of your substances tough to identify as polar or nonpolar? Explain.
Sometimes it’s useful in real life to mix things together that dissolve. Sometimes things are mixed together because they don’t dissolve. Give an example of each scenario and determine why the substances do or do not dissolve.

Conclusion

Now that you’ve collected data and analyzed it, answer the problem.

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