My husband showed H what happens when you mix baking soda and vinegar a while back and she was totally impressed. only problem she wanted him to do it again and again. So I came up with this solution. I poured some baking soda in a baking pan and I put water in one container with blue food coloring and vinegar in another with purple food coloring. I gave her an eye dropper and we experimented. We talked about what we thought would happen with them and then looked at the differences in the reaction of the water and baking soda vs the vinegar and baking soda. She loved it and was able to see it happen over and over. When she was tired of playing with it we did a grand finally and poured all the vinegar left over in the dish!