When calcium chloride and baking soda are mixed with water, a chemical reaction occurs forming carbon dioxide gas and calcium carbonate precipitate. When citric acid and baking soda are mixed with water, carbon dioxide gas is produced. These observations provide evidence that chemical reactions took place, changing the reactants into new products. Atoms are the basic particles that make up all matter, and molecules are formed when atoms combine together.

1. Focus Question: What happens when you combine different chemicals? Fizz Quiz Investigation3-1