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.
Entries in chemistry (25)
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.
A dollar bill is soaked in 2 parts water, 2 part isopropyl alcohol, and then lit. The liquid burns off, but the dollar bill doesn't ignite. Watch the video for an explanation.
Two things I love: chocolate and science. This video shows you how to make chocolate pop rocks. Pop rocks was a crazy new candy when I was a kid. Put them in your mouth and let the crackling begin. Pop rocks is basically a mixture made when sugar and water are heated and then injected with carbon dioxide gas. The cooled mixture is the pop rocks. Put them into your mouth, the sugar disolves and the carbon dioxide gas gets released (the pop). Chocolate is a complex mixture of many ingredients, primarily sugar, cocoa butter, cocoa liquor, milk or milk powder (for milk chocolate), and vanilla. Chocolate can be melted and mixed in with other ingredients to make many different flavor combinations. Basically this demo shows how to properly melt (temper) milk chocolate and mix in flavorless pop rocks (called pastry rocks). The results are delicious pieces of chocolate that melt in your mouth which lead to a suprise crackling of the pastry rocks. Science topics that are covered include energy in phase changes, properties of mixtures, and crystalization (chocolate has to reach specific temperatures in the melting process so that cocoa butter crystals form evenly).
I recently started a food science club at school with a fellow teacher. It's a good way for me to try out new stuff with a small group of students, that I eventually want to incorporate into my classes. It's like a real life R and D department. I recently posted about a polymer called sodium alginate. I got a response from Earl Lee on how to make watermelon caviar. So I decided, let's try it out with an after school club. It demonstrates a technique used in molecular gastronomy. A polymer (which is in one of our standards), sodium alginate, is mixed in with watermelon juice. The mixture is then carefully inserted, with a syringe, into a solution of calcium chloride. A chemical reaction happens between the calcium chloride and sodium alginate to form calcium alginate. The calcium alginate is not soluble in water and thus forms a gel around the outside of the watermelon juice. The calcium alginate watermelon spheres are edible. We then experimented with making spheres of cola using the same technique. The students loved the more intense (not to mention the more sweet flavor which their palettes are more geared to) flavor of the cola.