Reaction of halogens with cold alkali

All the halogens react readily with alkalis. The products depend on the temperature at which the reaction takes place. The reaction between chlorine and cold sodium hydroxide solution is used in industry to remove waste (poisonous) chlorine gas. The product of this reaction, sodium chlorate(I), is used in bleach manufacture. The following videos show the reactions of cold sodium hydroxide solution with each of the halogens. You will see easily the colour changes which occur with the bromine and iodine. However, as the chlorine solution is very pale green, and turns colourless, it is difficult to see any change. It is easier to detect that a reaction has taken place, and that the chlorine has been used up, by using your sense of smell to spot the disappearing chlorine smell. This doesn't work well on video, so no video is provided for this reaction.