Question

What is the oxidation no. of Cl in FeCl3.H20?

Answer 1

-1

Explanation:

Fe Iron has oxidation numbers of +2 and +3.
Combining with Iron Chlorine will have a negative charge Oxidizing the Iron.

The most likely charge of the Iron is +3 which gives the Chlorine a charge of -1

Answer 2

Are we agreed that the sum of the oxidation numbers should equal the charge on the iron complex?

Explanation:

The sum of the oxidation numbers in a complex or chemical species, is ALWAYS equal the charge on the ion or species or complex. Here, we gots a ferric chloride derivative, i.e. `[FeCl_3*OH_2]`, which we could break up to give `FeCl_3` and `H_2O`...

Now chlorine comes from Group 17 of the Periodic Table and it commonly forms a `Cl^(-)` ion... And so given that ferric chloride is neutral...`0=Fe_"Oxidation number"+3xxCl_"Oxidation number"`...and so …

`3+=Fe_"Oxidation number"`, i.e. `Fe_"Oxidation number"=+III`..and so...

`-3=+3xxCl_"Oxidation number"`

MOST of the time chlorides have this `-I` oxidation state...which we could formally approach as...

`1/2Cl_2 + e^(-) rarr Cl^-`...

i.e. zerovalent chlorine undergoes one electron reduction to give `Cl^-`...