Dig into the chemical properties and reactions involved in concocting a beloved dessert with a fun look at changing states of matter.

SUMMARY OF CLASSROOM LEARNING
Students have been learning about physical properties and states of matter. This extra do-ityourself treat also serves as a simple chemistry lesson. Investigate changing states of matter, chemical reactions, and the properties of ice and salt while working for your dessert.

OBJECTIVE
Students are able to:
• take the temperature of a liquid.
• observe and describe the changes in states of matter.

BACKGROUND INFORMATION
Salt makes ice melt. That’s why people sprinkle it on icy roads and driveways in cold climates. How does salt do this? It actually lowers the freezing point of the ice. Water normally freezes at 32 degrees Fahrenheit, or 0 degrees Celsius. Salt water is harder to freeze than plain water. You have to make salt water colder than 32 degrees Fahrenheit in order to freeze it. That’s one of the reasons why a freshwater pond will freeze before one that’s mixed with salt water from a nearby ocean. If you put two ice cube trays in the freezer, one with plain water and the other with a salt water solution, the plain water will freeze first. Not all types of salt work the same. The larger the salt crystals, the more time it takes to dissolve. This keeps it colder, longer. As salt melts, the compound (NaCl) breaks into two parts—Na and Cl. These particles then disrupt the arrangement of the ice crystals. This process changes the state of matter. For example, the liquid (milk mixture) turns into a solid (ice cream). As the liquid gets colder it expands. (Have you ever put a soda bottle in the freezer and forgotten about it? The liquid expands and then explodes!) The molecules in the liquid slow down and eventually freeze in place.

HOME ACTIVITY
Make ice cream as a family. Observe and discuss the changes that occur in the states of matter and temperature.

Grades K – 2