In this promising practice lesson students explore chemical change. Students combine calcium chloride, baking soda, water, and an acid indicator in a Ziploc bag and observe what happens. Students take temperature measurements before and after the reaction. They also record their qualitative observations. Students then decide, based upon the evidence, if a physical or chemical change has occurred.

At the beginning of the lesson the teacher leads a discussion about what qualifies as a good scientific observation. As a result of the discussion students recognize that good scientific observations are objective and free of opinion. It is important that students learn to make and be able to describe observations objectively.

It is recommended that the teacher experiment with different sizes of bags to determine which size works best prior to conducting the lesson. (ts)