Chemical Reactions: Synthesis
Getting Started
Students may not have formulated a mental model of atoms or molecules at this stage. Typical textbooks show these as spheres that have certain electrical properties. In this next set of explorations we will address chemical change first as a nature of change of properties and then deal with the model later.
An Analysis Exploration
1) Give students two samples, one iron powder or filings and the other sulfur. Have them examine their characteristics and, if there is ample time, allow them to test the substances as you would the white powders.
2) Have students record their characteristics on a data table.
3) Demonstrate a process of placing equal amounts of sulfur and iron in a test tub and mix. Students can do this with a small amount of their samples provided. Observe any change. They should note that they can still see the yellow sulfur and the black iron--there is no change. This is a mixture then. If you have them take a magnet they can remove the iron. It is unchanged.
4) Students should record their results and observations and be able to define a chemical mixture.
5) Prepare a test tube with sulfur and iron. Use a torch or bunsen burner and test tube holder to heat the mixture. If you are unable to do this demo live, show the class this video:
6) When the reaction is over, dunk the test tube into a cold water bath. The tube should break and the Iron and sulfur (now a compound or molecule of Iron Sulfide) can be removed and given to the students.
7) If the demo will not be conducted in class, distribute iron pyrite samples to the students for examination, Again, the students can pulverize some parts of the pyrite and then test it as they did the sulfur and the iron. How are its characteristics different?
What was created in this process is a new material. A compound of iron and sulfur that has different characteristics than sulfur or iron. We have conducted a chemical change. In this reaction, heat was required to bind the two elements. Now we have a new material called FeS, or iron sulfide. In nature the compound is called iron pyrite, or fool's gold.
Sometime chemical reactions require heat, sometimes they produce heat. There are always exchanges of energy in a chemical reaction.
