To prepare some of our favorite foods, such as ice cream, birthday cakes, and even barbecued steaks, we rely on chemical reactions. Some of these reactions occur when food ingredients combine, while others result from cooking or cooling processes. When we understand how science affects foods, we can create tasty new recipes.
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 degrees C. A saturated saltwater solution freezes at -32 degrees C. If you sprinkle salt on ice, the ice will melt because the salt lowers the freezing point of water. When the salt makes contact with the ice, it starts a chemical reaction that transfers heat energy from the surrounding environment. Therefore, if a road is icy in the winter and we sprinkle salt on top of it, the salt-ice mixture will draw heat energy from the road, the air, and the friction from car tires and transfer it to the ice, which then melts.
Have the students sprinkle some coarse salt on a piece of ice. As the ice begins to melt, discuss what is happening. Ask them if they have ever seen this chemical reaction before. Perhaps some of the students have seen salt on the streets in winter. Introduce the idea of using the chemical reactions between salt and ice to super-cool the ice cream mixture when making home-made ice cream.
Vanilla Ice Cream Recipe
Relate this activity to your community by organizing a tour of a local ice cream factory. If there are none in your neighburhood then you might look for another type of food manufacturer or even invite a food chemistry specialist into your classroom.
Experiment with baking powder and show how chemicals can be used not only in the preparation of food but also as key ingredients in recipes. Corn bread is a simple food, easily prepared by students, that illustrates basic chemistry. It includes active chemicals such as baking powder (a combination of corn starch, monocalcium phosphate and sodium bicarbonate) and buttermilk (acetic acid). Students can watch the reaction between these ingredients take place. You can talk about how the chemical reaction creates tiny air bubbles in most cakes.
Did you know that the process of freezing eliminates contaminants from water? Inuit people have tapped this phenomenon for centuries, making safe, clear drinking water from frozen salt water. Recently, Canadian engineers have created a sewage treatment system that relies exclusively on freezing, generating what they call “snowage”!