The penny lab is a simple easy to do lab that students tend to enjoy. I use each year as an intro type lab when talk over properties of water. It can be fit into topics that include the scientific method, valuable properties of water, surface tension, activity of soap (or NaOH), or just a general fun competition style lab.
Students enjoy trying to fit the most drops they can on the penny and using the concept of a controlled experiment to "discover" the valuable properties of soap and water.
small jar of pennies
liquid dish soap or detergent
paper towels (opt.)