Dilute and concentrated solutions are fairly common. Vinegar, soft drinks, and window cleaners are dilute solutions. Bottled laundry bleach, battery acid, and concentrated juices are concentrated solutions. In between are medium solutions such as mouthwash, perfumes, windshield washer fluid, and antifreeze.

 

Saturated solutions are not so common. Saturated solutions hold as much solute as possible, at a given temperature. If you’ve ever made home-made candy, you probably made a saturated solution. To make candy, you dissolve as much sugar as possible in hot water. If you can increase the temperature of the solution, it can dissolve more solute. But what happens if a saturated solution at a high temperature is cooled to a low temperature?

 

What happens when a saturated solution is cooled?

 

 

Sodium thiosulfate is poisonous.

 

1. Pour about 100 mL of hypo into one of the beakers.

2. Half fill the test tube with cold distilled water.

3. Use the scoop to add 1 mL of hypo to the test tube.

4. Shake the test tube until all the hypo dissolves.

5. Repeat steps 3 and 4 until the cold solution will not dissolve any more hypo. (How many scoops of hypo can the cold solution dissolve? What kind of solution is this?)

6. Now use the Bunsen burner to gently heat the solution in the test tube. Do not boil the solution.

7. Repeat steps 3 and 4 until the hot solution will not dissolve any more hypo. (How many scoops of hypo can the cold solution dissolve? What kind of solution is this?)

8. Half fill another beaker with cold tap water.

9. Place the test tube with the hot hypo solution in the cold water to cool the solution. (Does a solid appear in the test tube?)

10. If a solid does appear in the test tube, reheat the solution until the solid dissolves again. Then cool it again in the cold water. You should have a cool solution, with no solid in it.

11. Use the forceps to select a tiny piece of hypo from the beaker of hypo.

12. Now drop the tiny piece of hypo into the cold hypo solution. (What happens in the test tube?)

13. Clean up your work area.

 

> How did you make the cold hypo solution dissolve more hypo?

> What happened to the tiny piece of hypo when you dropped it into the cold solution of hypo?

> What was the solid substance in the test tube at the end of the investigation? How did it get there?

 

By adding hypo to the water, you made a solution. With cold water, it did not take much hypo to make a saturated solution. However, by heating the solution, you could dissolve more hypo. Eventually you were able to produce a hot saturated solution.