In my class students learn about chemical reactions and also the difference between elements and compounds. Students learn that the 5 signs of a chemical reaction are: 1) color change 2) gas production 3) precipitation 4) temperature change 5) change in properties (smell, texture, taste, density, etc.) Students also learn that compounds are chemicals that have 2 or more elements bonded together, such as water. In this demonstration, students observe water undergoing a chemical reaction, and breaking apart into hydrogen and oxygen gas. This demonstration can be done on an overhead projector so that all students can view it easily. The materials needed for the demonstration are shown below.
This is a simple demo that doesn’t require any special equipment. As the electricity goes through the water, molecules of hydrogen gas and oxygen gas form at the separate ends. The bromothymol blue solution changes color only at one of the ends, indicating the gasses are not the same. More hydrogen gas bubbles appear on one of the ends as oxygen gas bubbles on the other end. This clearly indicates the ratio of hydrogen atoms to oxygen atoms in water is 2 to one. Tip: Dissolve some salt into the water to aid in electricity flowing through the water.