[Asum]

I'm supposed to find the ox. no of Cl on each side:

Cl₂ (g) ---> Cl ^- (aq) + ClO^-₃ (aq)

I know that on the left the ox. no is 0 and Cl ^- on the right has -1
but what's the ox. no to Cl of ClO^-₃ ? And how do you find it?

thx

[rabolisk]

A useful rule is that the oxidation number of oxygen is usually -2, except when it is bonded to fluorine (which is more electronegative) or is a peroxide or superoxide.

[opti384]

You are right rabolisk but in this case I think the oxygen will stick to the original -2 because oxygen is more electronegative than Cl.

[Borek]

You are right rabolisk but in this case I think the oxygen will stick to the original -2 because oxygen is more electronegative than Cl.

That's what he wrote in case you missed it.

[Fluorine]

how do you find it?

Check this link for a easy to follow set of rules to help you determine oxidation states. When you're unsure if an element can take that state try Wikipedia's "list of oxidation states of elements".