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Lesson 2.4 What is The Best Solvent?

You learned that substances such as oil will not dissolve in water. Similarly, petroleum jelly and other oil-based products will not dissolve in water. This investigation will determine what is the best solvent for petroleum jelly and salt.

Read the investigation on page 48 of your textbook. Perform the investigation. If you do not have access to a supervised laboratory make the following modifications.

Materials and Apparatus Modifications:

路 Use a stove element instead of a hot plate.
路 Use a pot rather than the 100mL beaker.
路 Use a glass measuring cup instead of the test tubes and the graduated cylinder.
路 Use jar tongs or a pot holder in place of test tube tongs.
路 Use spoons instead of the scoopulas and stirring rods.

Question 1. Answer questions 1, 2, and 3 in Analyze on page 49.

Question 2. Water and oil are not soluble in one another. If an unknown substance will dissolve in water, do you predict that the substance will dissolve in oil?

Check your answers with those that follow.

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Answers to Questions:

Question 1. Answer questions 1, 2, and 3 in Analyze on page 49.

1a. Yes, the salt dissolved in water.

1b. No, the salt did not dissolve in vegetable oil.

2a. No, the petroleum jelly did not dissolve in water.

2b. Yes, the petroleum jelly dissolved in vegetable oil.

3. Heating did not make any of the insoluble substances dissolve. That is, the salt did not dissolve in the oil when it was heated, and the petroleum jelly did not dissolve in the water when it was heated.

Question 2. Water and oil are not soluble in one another. If an unknown substance will dissolve in water, do you predict that the substance will dissolve in oil?

If the unknown substance dissolves in water, it will not likely dissolve in vegetable oil because water and vegetable oil are insoluble. Note that a few substances will dissolve in both water and vegetable oil (recall how soap works).


Click on the page forward to continue Lesson 2.