water and ice are at equilibrium at 0C but adding salt lowers the freezing

Water and ice are at equilibrium at 0c but adding

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water and ice are at equilibrium at 0°C, but adding salt lowers the freezing point and thus lowers the equilibrium temperature. When you add more salt, the equilibrium temperature drops even lower. This is why salt is used to melt ice on roads during the winter. In order for the ice to melt, it must absorb heat energy from its surroundings. This causes the temperature of the mixture to drop, and the mixture freezes. Hypothesis : How does making ice cream demonstrate exothermic and endothermic reactions? Materials (per pair) : ¾ c. whole milk 2T Whipping Cream 3T. sugar ¼ t. vanilla Quart zip-bag Gallon zip-bag 4 cups ice 4T. rock salt Gloves or towels Thermometer 2 spoons Procedure : 1. Mix the whole milk, sugar, and vanilla in the quart bag. 2. Seal the bag tightly, allowing as little air to remain in the bag as possible. 3. Place the quart bag in the gallon bag and add the ice and salt. Again, let the air escape and seal the bag tightly. 4. Wrap the bag in the towel or put your gloves on, and shake and massage the bag, making sure the ice surrounds the cream mixture. 5. Watch the clock and record the temperature of the ice mixture every minute by carefully opening a small area of the gallon bag and placing a thermometer into the ice/salt mixture being careful not to puncture the bag.
6. Record the temperature. Remove the thermometer and re-seal the bag. Continue shaking and massaging the bag until the ice cream begins to form a solid. 7. Record the last temperature and get you teacher’s permission to eat your experiment. 8. Create a graph of your data. Place the time on the x-axis, temperature on the y-axis. Be sure to include labels on your axes and a title. Data Table Time (min.) Temperature (°C) Analyze and Conclude : 1. Was your hypothesis correct? Why or Why not? 2. How does the graph support your understanding of endothermic and exothermic reactions? 3. How does this lab relate to the use of salt on roads in the winter?

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• Fall '19
• Thermodynamics, 0°C, 4 cups, ice cream lab, Nancy Johnson

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