 In the flask I have some distilled water. I'm going to add some glucose to the water. I'm going to swirl this and have the glucose dissolve. Glucose is a sugar. Glucose reacts with the oxygen in the air slowly to produce carbon dioxide and water. If I add some potassium hydroxide, the potassium hydroxide acts as a catalyst to speed up the rate at which the glucose reacts with the oxygen in the air. I'm going to add a few drops of an indicator called methylene blue. Methylene blue is blue in the presence of oxygen and is colorless in the absence of oxygen. I'm going to swirl the flask and let it stand for a few minutes. I'm going to swirl the flask again and let it stand. Swirl the flask and let it stand. Explain what's happening in the flask.