The most used science fair project, and a kid favorite because it's messy, is the erupting volcano. First, a paper mache volcano is made. One way is to use a square of cardboard for the base and put a plastic bottle, perhaps seven or eight inches tall, in the middle. Use masking tape to run strips from the top of the bottle to the edges of the cardboard. This makes a "web" that holds the paper mache strips.
Paper mache paste uses one part flour and one part water, along with a tablespoon or two of salt to prevent mold. When mixed, it forms a paste-like liquid that's perfect for dipping strips of torn or cut newspaper. Once the paper is covered, it goes on top of the volcano web, making sure to leave the bottle opening clear. The volcano needs to dry and harden overnight, then it's ready for painting.
The bottle in the middle is used to hold the vinegar, baking soda, dish soap and food coloring that create the lava. Do not add the ingredients until the project is set up on a covered table or even outside. One cup of vinegar goes in first. Using about 10 drops of food coloring, half red and half yellow, creates orange lava. Adding a couple squirts of liquid dish soap makes the lava extra foamy, but this is optional.
When the display is ready, four tablespoons of baking soda, measured and waiting in a container, are poured in all at once. The result is one orange-red, foamy eruption. The experiment shows the reaction when an acid, the vinegar, is mixed with a base, the baking soda. The two ingredients release carbon dioxide gas that creates the eruption.