The kids started off with calcium chloride, sodium bicarbonate (see if your kids remember this compound's common name...it's baking soda), water, and phenol red, an indicator for acids. They put all of these materials in a plastic bag, the catch being that the liquids (water and phenol red) were first poured into plastic cups, which themselves were carefully placed in the bag. Why all the extra steps? This allowed us to measure the whole business BEFORE the chemical reactions began. After tying off the bag, the kids allowed the powders and liquids to mix, and that's when things got exciting! The kids observed many changes including: bubbles, the bag inflating, the red liquid turning yellow, and the contents both heating up and cooling down. The kids then measured the weight of the bag with its contents, and they were pretty surprised to find very little if any change. That's conservation of mass for ya! Step 2 of this experiment was breaking down the reaction into parts to see what happens when you combine different pairs of ingredients.