question about the back titration of vitamin C

Question

why we need to use iodine but not other halogens to oxidize vitamin C?
is it relay to the unstable of the vitamin C? and how?
thank you very much!

Answer 1

Firstly, iodine is the safest one among the halogens. Fluorine is extremely reactive and can even react with water (in our body). Chlorine is poisonous. Bromine vapour is very toxic and corrosive.

Secondly (the most important point), the technique of titration of excess iodine against sodium thiosulphate solution using starch as indicator is a well developed technique. Therefore, it is easy to determine the amount of ascorbic acid (vitamin C) by using the back titration of iodine.

Lastly, I don’t know what do you meant by “and how ?”.