how2GASES Experiments 

Progression #4:  Comparing the Density of Hot Versus Cold Water.   As noted in the how2GASES introduction warm air is less dense than cold air.  Is this also true of warm (hot) water and cold water?  A simple experiment can be used to demonstrate the property of density using warm and cold water.

Density Demonstration. 

For Version 1 you will need four (4) small baby food jars, food coloring and two (2) plastic-coated playing cards or similar type cards.

- Overflow two of the baby food jars with cold blue-tinted water and the remaining two baby food jars with warm (or hot) red-tinted water.

- Place the plastic-coated playing card on top of one of the baby food jars containing cold water (blue) and another on top of a baby food jar containing warm water (red). Gently tap down each of the cards to create a seal.

- Starting with the card-covered baby food jar containing the warm (hot) water, quickly invert the jar and gently place it on top of the baby food jar filled with cold (blue) water. Leave the card in place between the two jars until you have repeated the same procedure for the baby food jar with the blue-tinted water.

- Carefully remove the cards from each setup. Have your class observe what happens in each setup.

Why does water move in only one of the setups? Hot and cold water display similar density properties as hot and cold air. Hot water is less dense than cold water and as such it moves from the lower baby food jar into the top jar. Conversely, the cold water, which is denser will sink. In the other setup, the hot water is already in the top position and remains in place. Note: Over time, the other setup (cold on the bottom) will also eventually mix together. This is the result of passive diffusion as the temperature equilibrates (becomes the same) between the water in the upper and lower baby food jars.

For Version 2, you will need two tall glass or clear plastic cylinders or containers that are large enough and tall enough to accomodate a narrow-necked vase or baby food jars.

- Fill one cylinder with warm (hot) water and the other with cold water.

- Create a handle for the baby food jar or narrow-necked bottle. A handle can be fashioned out of pipe cleaners.

- Fill one submersible container with blue or red-tinted cold water. This will be submerged into the cylinder containing hot water. Fill the other submersible container with red-tinted hot water. This will be submerged into the cylinder containing cold water.

- Have your class observe what happens in each cylinder. The hot, red-tinted water submerged in the container containing cold water will rush upwards because of its lower density. And as described previously, the cold water submerged in the container containing hot water will remain in place for an extended period of time.

For feedback, comments or questions, contact how2team.

how2SCIENCE.com ã 2004 All Rights Reserved