In many experiments you have seen or done, you may have observed an increase in temperature. Heat energy is often associated with chemical changes.

Heat energy is also associated with some physical changes. For example, you need to add heat to water in order to get it to boil. In the Measuring Phase Changes Sci-ber text page, you experimented with heating ice until it boiled.

Now it is time for you to remove heat energy and observe changes. You should make careful observations to determine what physical and/or chemical changes you observe.

This activity will provide enough ice cream for about four people. Find some friends and have some fun!

Materials:

• Two quart size zip closure plastic bags
• Two gallon size zip closure plastic bags
• One pint of half & half (from the dairy section of a grocery store)
• 1/4 c. sugar
• 1/2 t. vanilla
• 1/2 t. salt
• Ice
• Rock salt
• Gloves (optional)
• Bowls
• Spoons
• Ice cream toppings (optional)

Procedure:

1. Carefully open one of the quart size bags.
   • Pour in the half & half.
   • Add the sugar, vanilla, and salt.
   • Squeeze as much air out as you can then zip the bag closed.
   • Carefully squeeze the bag back and forth to mix the ingredients.
2. Carefully open the second quart size bag and place the first bag inside.
   • Squeeze out as much air as you can and close the outer quart size bag.
3. Carefully open one of the gallon size bags.
   • Fill this gallon size bag about 1/4 full of ice
   • Determine how much rock salt you are going to add and record this number.
   • Place the two quart-size bags onto the ice and rock salt.
   • Add more ice on top of the quart size bags until the gallon size bag is about 3/4 full.
   • Determine how much more rock salt you are going to add and record this number.
   • Squeeze out as much air as you can and close the gallon size bag.
4. Carefully open the second gallon size bag and place the first gallon size bag inside.
   • Squeeze out any excess air and then zip the outer bag closed.
5. Gently use your hands (use gloves if you want) to move the ice and rock salt around the quart size internal bags.
6. Keep track of how long it takes for the inner bag ingredients to change from liquid to solid.
7. Carefully remove the bag with your ingredients in it.
   • Open and enjoy your product!
   • Place material for each person in a separate bowl and add any desired toppings.

Data:

• Total amount of rock salt added ______________________.
  
• Time until inner materials changed from liquid to solid ______________________.

Analysis:

1. What evidence of physical changes did you observe?
2. What evidence of chemical changes did you observe?
3. Why was the rock salt added to the ice?
4. What changes did you observe in the outer bag (that was filled with rock salt and ice?)
5. How would you describe the changes you observed in the innermost bag?
6. Did you add or remove energy from the materials in the innermost bag?
   • What evidence do you have to support this answer?