Changing Density

1. ChangingDensity Simon and Hecubus

2. Remeberthat… • Density: istheamount of mass a material has for a givenvolume. • Thispropertyisobviouswhenyoulifttwothings of equalvolumethathavedifferentmasses. • Density = mass/volume

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4. Materials (foreachgroup): • 3tbsps (45ml) baking soda • ¾ cup of warm water • 250 ml of vinegar • A clear glass (500ml+) • 3 halves of raisins

5. Procedure: • 1. Stir 3 (45ml) tablespoons of baking soda into ¾ cup of warm water. Set aside. • 2. Poor vinegar into a clear glass until it is half full. • 3. Slowly pour the baking soda and warm water mixture into the glass of vinegar. • 4. After most of the fizzing has stopped, place 3 halves of raisins in the glass. • 5. Record your observation under the Data and Observation section on the worksheet.

6. DancingRaisinExplained: •  Since the surface of the raisins is rough, tiny bubbles of carbon dioxide gas are attracted to it.  These bubbles increase the volume of the raisin substantially, but contribute very little to its mass.  As a result, the overall density of the raisin is lowered, causing it to be carried upward by the more dense fluid surrounding it. 

7. DancingRaisinExplained: • Since the raisins now have a greater volume, they displace more water, causing the fluid to exert a greater buoyant force. • The buoyant force of the surrounding fluid is what pushes the raisins to the top.

8. DancingRaisinExplained: • Once the raisins reach the top, the bubbles pop upon exposure to the air. • This makes the raisins more dense, causing them to sink. • As more bubbles adhere to the raisins, the density of the raisins decreases and they rise to the surface again.

9. DancingRaisinExplained: • This experiment very clearly shows that an increase in volume (as long as the mass increase is negligible) will lead to a decrease in density. • The bubbles that attach themselves to the raisins are like little life jackets that make the raisins more buoyant by increasing their volume.

10. Theend!