Mixtures

A major standard our students have to learn is the difference between elements and compounds. Compounds are substances that are made of two or more elements bonded together. The elements that comprise a compound have different properties when they are bonded together than when they are separated. Students have great difficulty with this. I introduce the unit by doing a simple activity on mixtures. Educational Innovations sells a simple Mixture Separation Challenge kit. Students are first forced to separate the mixture into 3 groups. Students usually use the simplest property of color to do it. There are other properties such as relative density or optical properties (opaqueness, transparency, etc.). The main idea is that the substances can be separated by their properties, because those properties do not change when forming a mixture, unlike when a compound is formed.

Conservation of Matter: Heavy Whipping Cream

I found a new way to teach the conservation of mass/matter this past year. Previously I taught it by having steel wool (iron) react with oxygen. Since our periods are shorter this year, I couldn't really do that reaction anymore. Now students mix heavy whipping cream and vinegar in an open system. The vinegar reacts with the casein proteins in the heavy whipping cream to form a solid cheese-like substance (basically it is cheese). It's not a very  glamourous reaction, but is also a way to teach students about precipitation. Students have a difficult time understanding the concept of two liquids reacting to make a solid. This is a simple way for students to visualize that type of chemical change.