Water “The Exception”

 Ice and Water in the Density Column

Directions  As you view this slide presentation, you will be asked to write notes in your notebook.  Please number each entry.  Write in complete sentences whenever possible.

Getting Started  In your notebook, write a brief description of the relationship between the volume of a substance and its temperature. Use complete sentences.  Rank the following from hottest to coldest: Room temperature water An ice cube Cold water

3. Video: Water Temperature and Density a. What do you observe about the density of hot water versus cold water? b. If colder substances are denser and sink then shouldn’t ice sink to the bottom of a tank of water? Hmmm…What is it about ice that makes it float?

4. Video: Time Elapsed— Freezing Water in a Beaker  Observation Notes

5. Video: Time Elapsed— Freezing Water in a Bottle  Observation Notes

6. Video: Freezing Dynamics of Water  What do you see happening as the sample approaches the freezing point?

7. Bursting Pipe--Application  Why must we sometimes leave faucets dripping on VERY cold nights?

8. Make Graph Temp (°C) Mass (g)Volume (mL) Density (g/cm 3 ) Sinks or Floats in Surrounding 16°C Water xxxx Sinks Sinks! Sinks!!! 4 (omg!) Ice bonds form — Expands, rises! Floats!!!!!  Calculate the Density and then make a graph with Temperature on x-axis and Density on y-axis

Density of Water Graph

9. Conclusion What do you conclude about the density of water and temperature?

ICE is bigger than liquid water  Liquid water molecules can move around and get close together.  Ice forms a rigid hexagonal crystal that takes up more space than liquid water.  Since ice has greater volume it is less dense than the same amount of water.

Why does ice float?  Centigrade means “100 steps”  Centigrade is the old name for the Celsius scale

The Anomalous Expansion of Water  What does “anomalous” mean? Unusual, out of the ordinary Unusual, out of the ordinary

Summary Water freezes at 0ºC. Imagine you have water that is at room temperature (22ºC). You remove heat from it (cool it) and the water contracts. The volume decreases, making the density increases, and the colder water sinks. BUT, once cooling water reaches a temperature of 4ºC solid ice bonds begin to form. When this happens the molecules become farther apart and the water begins to expand again. This means its volume starts to increase again, the density drops. This is why ice floats—it is less dense than water. Ice forms a protective insulating layer above ponds and lakes in the water, and actually keeps some heat in the body of water, allowing critters to survive. If water didn’t expand when it froze then ice wouldn’t float—it would sink! This means that ponds and lakes would freeze from the bottom up and all the critters would freeze solid in a block of ice if the temperature were cold enough. This obviously doesn’t happen. If not for this bizarre property of H2O life would not exist! Hmm.

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