This Easter I had the lofty goal of dying eggs with food, using beets for pink, turmeric for yellow, and red cabbage for blue. Like many things, my kids had different ideas, thus we did not dye eggs. That didn’t stop us from having lots of fun with colors. I took the cabbage juice to use as a pH indicator and had some fun with my youngest.
Our red cabbage water started out a beautiful blue color. During our first experiment we just added different substances that I knew would give a nice array of colors: citric acid, vinegar, baking soda, ammonia. But eventually she wanted to mix things together. This is not a safe thing in chemistry unless you know what is going to happen. I still wanted to let her have that experience, so I rinsed the tubes and we started all over again, this time with only baking soda and citric acid.
I encouraged her to mix them any way she liked. She loved it and the results were amazing! It kept her occupied for a nice long while. We talked some about chemical reactions and a tiny bit about pH, though pH is really a bit complicated for a five-year-old. This would be well suited for an older child as well. Here are a few more photos of her play.
In the picture above you can see the classic bubble reaction when adding citric acid (or vinegar) to baking soda. The molecules are breaking apart and forming new molecules. Some of these new molecules are carbon dioxide which is a gas, and thus bubbles out of the solution.
In the picture above you see the graduated colors where the solution isn’t well mixed. This is likely due to density. You’ll notice when you add citric acid to the blue/purple cabbage water, it swirls and mixes gradually until the whole solution is mixed. I’m guessing because the citric acid solution is more dense than the cabbage water. This doesn’t always happen when you add the citric acid to a baking soda solution. Sometimes the densities keep them from mixing fully and you have this graduation in color. Check out “density towers” on the web to learn more about it.
Below are some links that might be useful to you if you decide to try this at home.
The Experiment Peformed by the Sci Guys They blended their cabbage, but I just chopped it up and boiled it in some water, draining the cabbage out afterwards.
An explanation of pH by Bozeman Science This is material for an older child or an adult