Natalie Roman 

H-23 

5/5/14

Background: 

Certain substances affect the state of ice.  When salt is sprinkled on ice, for example, it causes the ice to melt.  This chemical reaction is actually a heat energy transfer.  Water freezes at 0°C. A saturated saltwater solution freezes at -32°C.

Objective:

To develop observation skills, understand the scientific process through active experimentation and comparison, and understand that chemicals can change the properties of water.

Materials:

• 1/2 cup milk
  
• 1/2 cup whipping cream (heavy cream)
  
• 1/4 cup of sugar
  
• 1/4 teaspoon vanilla flavoring
  
• 3/4 cup of sodium chloride as table salt or rock salt
  
• 2 cups of ice
  
• 1 quart Ziploc bag
  
• 1 gallon Ziploc bag
  
• Thermometer
  
• Measuring cups and spoons
  
• Cups and spoons for eating your homemade ice cream
  

Procedure:

1. Add the 1/4 cup of sugar, 1/2 cup of milk, 1/2 cup of whipping cream, and 1/4 teaspoon vanilla to the quart size Ziploc bag.
2. Put 2 cups of ice into the gallon size Ziploc bag.
3. Record the temperature of the ice using the thermometer.
4. Add 3/4 salt to the gallon size Ziploc bag that is filled with ice.
5. Put the quart Ziploc bag into the gallon Ziploc bag and close securely.
6. Shake the bag back and fourth for 10-15 minutes until the content of the quarts bag have solidified into ice cream. ** you might want to use gloves because the bag will be extremely cold.
7. Use the thermometer to record the temperature of the ice and salt in the gallon Ziploc bag.
8. Take the quart Ziploc bag with the ice cream component, serve into cups, and eat it!

Data:

1. What kind of ice cream are you making?Vanilla
2. Document the temperature of the gallon bag before adding the salt. 0 degrees Celsius
3. Document the temperature of the ice/salt mixture in the gallon bag when the mixture begins to solidify. -10 degrees Celsius
4. What is the temperature difference before adding the salt and after mixing for 5 minutes?-10 degrees Celsius
5. . What is the temperature difference before adding the salt and after mixing for 10 minutes? -9 degrees Celsius

Conclusion questions:

1. What kind of chemical reaction is the process of ice cream making, as done in our lab? Explain why. Heat is removed from water and the temperature will drop because of adding salt. The molecules begin to move more slowly until 0 degrees Celsius than it will begin to solidify.
2. Explain why salt water is harder to freeze than plain water. Salt water is harder because the salt molecules requires a lower temperature to freeze
3. Is the process of making ice cream a physical or chemical change? Explain your answer. It is a physical change because all the chemical composition that we started is still there which means it only changed the form.
4. Why is salt used with the ice instead of sugar? Salt lowered the freezing point of the ice this makes the ice colder than it was before. Sugar does not dissolve well in cold water and sugar does not dissolve into multiple particles that are better at lowering the freezing point of a substance because the added particles have a better impact to form crystal ice.

Source:

• about.com
• ask.com
• youtube.com
• kentchemistry.com
• pubs.acs.org