The Student Room Group
Reply 1
tiger_vio
This question is driving me mad

'Give the oxdiation states of chlorine in Cl2 and HClO'

I know that in Cl2 it's 0, and in HClO its +1, but I have no idea why.
My teacher said its because Cl2 lost an electron, but I have no idea why!

Oxidation states are concerned with how much charge an element in a compound should have to make the compound neutral. Cl2 occurs naturally, halogens come in pairs and since the compound has only Cl as the element it is 0. In HClO, pick the common H element which will always have +1 state and O which will always have -2 state (memorise these) and then +1-2 = -1, and since we don't want a negative charge on the compound we cancel this by having a +1 charge on Cl so -1+1 = 0 will be the charge of the compound.
(1) All elements and compounds (eg. CL2, SO2) have an oxidation state of 0
(2) The oxidation state of an ion is equal to its charge (so CL- is -1, MnO42- is -2)
(3) H in a compound is always +1, Na and K are +1, O is -2 etc etc

Therefore

Cl2
Cl2 is 0 because its an element.

HClO
The oxidation state of chlorine in HClO can be worked out as follows...

HClO has an overall charge of 0 because its a compound.

You can split it up into its components so...

H + Cl + O = 0

You know H is +1 and O is -2 so...

+1 + Cl + -2 = 0

Simple rearrangement will let you figure out that the Cl in HClO is +1.
Reply 3
thanks to both of you :smile: got it now :biggrin:

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