PHYS320 Lab 17 Change of Phase
Experiment 1: Freezing and Melting
1.How does the addition of salt affect the equilibrium temperature of the ice water mixture?
2.Was there any difference in the amount of condensation that collected on the outside of each cup? Describe why this occurs, and what it suggests about the temperature of each mixture.
3.Compare the temperatures of the two mixtures over the duration they were in the freezer. Is this what you expect? HINT: what is the coldest temperature either mixture can reach given the freezer temperature?
4.Did either cup completely freeze after 30 minutes? How does the addition of salt appear to affect the freezing point of water?
5.In order to freeze an ice cream mixture, its temperature must be brought below approximately -3°C. Explain how surrounding the ice cream in salty ice water brine helps it reach this temperature.
6.Based on what you have observed, explain why it is helpful to spread salt on icy roads and sidewalks in the winter.
Experiment 2: Clouds in a Bottle
1. Did anything happen when you squeezed the bottle the first time?
2. What happened when you squeezed the bottle after dropping the match in?
3. Explain how the smoke helped the water vapor condense.
4. Clouds are the most visible when the tiny condensed water molecules are densely packed, making a reflective layer that appears white. What would you have to change in this experiment to make your cloud more visible? Hint: how is the density of a gas affected by temperature and pressure?
5. What changes to the air in the bottle allowed condensation to take place?
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