Summary

In this lab, students will investigate how dissolving salt (sodium chloride) in water changes the freezing point of the solution. While investigating this, they will make ice cream from small coffee creamer cups.

Grade Level

Elementary School

Objectives

By the end of this lab, students should be able to

• Understand that dissolving chemicals in water changes the freezing point of the solution.
• Identify phase changes, such as melting and freezing.
• Describe the meaning of a solution, and identify the solute and solvent in a situation.

Chemistry Topics

This lab supports students’ understanding of

• Solutions
• Freezing-Point Depression
• Properties of Matter
• Phase change
• Freezing
• Melting

Time

Teacher Preparation: 1 hour

Lesson: 45 minutes

Materials

• 1 Individual, sealed cup of Liquid Non-Dairy Creamer for each student
• Empty Wide Mouthed Bottle with lid (squeeze bottle, as shown in photo work best), 1 bottle for every 2 students.
• Quart sized zip-lock bags can replace bottles (do not recommend for young students)
• Water
• Rock salt (table salt will work also)
• Measuring spoons:
  • ¼ Tablespoons if using a small bottle
  • ½ cup if using quart bag or large bottle
• Ice ( Approximately 15 pounds for 20 students)
• Ice chest
• Thermometer 1 for each group

Safety

• Always wear safety goggles.
• Students should not drink the salt water solution
• Students should wash their hands thoroughly before leaving the lab.

• When students complete the lab, have students dispose of the salt water into a sink.
• Do not consume lab solutions, even if they are otherwise edible products.
• Normally, eating materials used in a science investigation is discouraged.
• You should take great caution if allowing students to eat materials used as part of the activity. Any items that have been in contact with classroom equipment should not be consumed.
• It’s advised that you set aside extra quantities of the edible components instead of eating items directly used in the activity. You should also be sure to check for allergy restrictions among students.

Teacher Notes

• I recommend that you do not do this lab in the science lab setting. Students should not eat in a science lab. For the least amount of mess/clean-up, it works best outside. The cups will sweat quite a bit and will get very messy. Some of the lids did pop off during the process.
• Make sure to have plenty of ice available, as it melts, student can add more to their container. I used about 15 pounds for 20 students.
• There are a lot of options for brands, and flavors of creamers to use. I used the Stone Cold Vanilla flavor! It tasted just like ice cream.
• If bottles with lids are not available, quart sized zippered bags will work, but I don’t recommend using the bags with young students.
• Make sure to have excess salt on hand, it is necessary for the process to work correctly.

Background information:

• The salt is added to ice and lowers the freezing point and temperature of water from 0°C to –10°C. Packing the creamer cup in ice, water, and salt and then swirling to lower the temperature evenly through the cup, results in an iced creamer cup.
• Most things on earth are liquids, solids, or gases, which are the three states of matter. States of matter can change from one to another through melting (solid to liquid), freezing (liquid to solid), evaporation (liquid to gas), boiling (liquid to gas), condensation gas to liquid), sublimation (solid to gas), and deposition (gas to solid). Substances have a temperature point where each of these phase changes occur. For this experiment, freezing point is a crucial concept.
• Freezing point is the temperature at which a liquid becomes a solid. The freezing point of water is 0°C. The process of freezing deals with lowering the temperature so that molecules of a liquid slow down enough that their attractions hold them together as a solid. For most liquids, the molecules in the solid state are closer together than they are as a liquid. But water is different. In ice, water molecules are actually a little further apart than in liquid water.
• Pure liquids, like water, are not the only liquids that can be frozen. Solutions can be frozen as well. Solutions consist of solutes and solvents. A solute is the substance dissolved, while a solvent is the substance that the solute dissolves in. For example, when salt dissolves in water, salt is the solute, and water is the solvent. When a solute, such as salt, is dissolved in water, the solution requires a lower temperature to freeze. So if salt is added to ice, the ice that melts will require a lower temperature to freeze again so more ice melts than refreezes. That’s why salt is put on icy roads in the winter.
• Also, if you have a mixture of ice and water at about 0 °C, adding salt will actually make the temperature of the ice and saltwater mixture go down.
• This is known as lowering the freezing point, also called “freezing point depression”.
• For this lab, it is important to lower the freezing point to make ice cream. Ice cream forms at temperatures lower than 0 degrees Celsius. Making ice cream without a freezer is difficult to do with ice formed from pure water because the solid ice is at about zero degrees Celsius. By lowering the freezing point by putting salt on ice, a water-salt-ice solution is formed which is lower than zero degrees and will allow the ice cream to freeze.