A reflection on simple chemistry
Here is a fun experiment you can do at home. Take a bottle of Coca Cola and add some milk. Wait for a while and you will get a strange mixture in the bottle. The bottom is covered by a snot-like substance, while the remaining liquid becomes transparent. What is happening here?
Because I have a (short) history as a chemistry teacher, I wanted to find out what reaction is taking place. And it turns out to be quite simple. The phosphoric acid in the Coca Cola reacts with a protein in milk called casein. The phosphoric acid molecules attach to the protein and become more dense. That is why they sink to the bottom and form a snot-like substance. You can trigger the same reaction if you mix milk with other acidic liquids, such as vinegar or lemon juice.