chlorine bleach

Because oxidation and reducation can only be referred to ATOMS when you are referring to the definition of oxidation/reduction as involving a change in oxidation number.

So, you can say that chlorine atom in OCI− is reduced because its oxidation number is reduced from +1 to -1, but you cannot say that chlorine bleach is reduced.

Also, in the equation: OCI− + CI− + 2H+ --> CI2 + H2O

Cl has an oxidation no. of +1 in OCI−, but its oxidation number in CI− is -1. So when you are referring to chlorine in general, it is both reduced AND oxidized at the same time, i.e. a disproportionation reaction.

Besides, chlorine bleach (OCI− ) only contributes 1 Cl atom to the reaction. The other Cl atom comes from HCl. So saying that OCI− is reduced to form Cl2 is not correct. You can only say that they REACT to form Cl2.

2007-02-14 22:11:41 補充：
By the way, Chlorine bleach is an oxidizing agent.

2007-02-14 22:12:53 補充：
Amendment. The second paragraph, oxidation number is reduced from 1 to 0.