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.

Flaming Colors

Students in my classes have to determine if a substance has changed physically or chemically. In order to do that, they need to know if the properties of a substance has changed. We can look at many different properties of a substance such as color, density, boiling point, melting point, taste, texture, hardness, etc. One of the most exciting properties of matter is the color in which they burn.  In the video above I show color flame candles and then show a demonstration of two different compounds, strontium chloride and copper sulfate, mixed with denatured alcohol, that produce large colorful flames.