When we blew gently into the cabbage water for several minutes, we observed that the color of the cabbage water changed from its original purple to a slightly lighter color. This indicates that the water is slightly more acidic.

What’s happening here? When carbon dioxide is bubbled through water, some of it dissolves into the water. That is, some of the carbon dioxide goes into the spaces between water molecules. A small proportion of this dissolved carbon dioxide creates carbonic acid, a weak acid. The slight change of color of the cabbage water caused by the carbonic acid indicates that some of the carbon dioxide is being stored in the water.

You can see this effect more clearly by using plain water and pH testing tablets such as those that come with the EarthForce water testing kit

After blowing into the water on the left for several minutes, we used the pH tablets to test a sample of water from each glass. The difference between the color of the water in the two tubes was very noticeable.

According to the pH card that came with the test kit, the water on the left that we blew into had a pH value of about 6.0, indicating a slight acidity. The original water was between 7.0 and 8.0, typical values for water from a faucet.

There are other ways that carbon dioxide can be stored in water. Here is a demonstration of one of them.

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