 We are curing chlorine gas by mixing sulfuric acid to bleach. Bleach contains hydrochlorosacin. Notice the yellow gas forming above the liquid in the Erlenmeyer flask. This yellow color is characteristic of chlorine. Don't try this at home. Chlorine gas is very toxic. As the chlorine gas is produced, it boils into a solution of potassium iodide. It is out of the color change that chlorine is replacing the bromine. The reddish brown color is characteristic of bromine. The chlorine and possibly some bromine gas bubbles into the second tube that contains potassium iodide. The color may look black in this video, but it is actually a deep purple. This color change is evident that chlorine is more reactive than bromine or iodide.