Balance the following equation by oxidation number method.

$bold space bold space bold FeCl subscript bold 3 bold space bold plus bold space bold H subscript bold 2 bold S bold space bold space bold rightwards arrow bold space bold space bold space bold FeCl subscript bold 2 bold space bold plus bold space bold HCl bold space bold plus bold space bold S$

Solution

(i) The skeleton equation along with oxidation number of each atom is
+3 -1 +1 -2 +2-1 +1-1 0
FeCl₃+ H₂S $rightwards arrow$ FeCl₂ + HCl + S
(Fe = +3) (S = 2) (Fe = +2) (S =0)
(ii) Noting the change on O. N. of above atoms
Increase S = -2 to 0 i.e. 2
Decrease Fe = +3 to +2 i.e. 1
(iii) Equalise the increase/decrease in O.N. by multiplying FeCl3 by 2.
$2 FeCl subscript 3 space plus space straight H subscript 2 straight O space space space rightwards arrow space space space FeCl subscript 2 space plus space HCl space plus space straight S$
(iv) On counting and balancing atoms on both the sides, we get the balanced equation.
$2 FeCl subscript 3 space plus space straight H subscript 2 straight O space space rightwards arrow space space space space FeCl subscript 2 space plus space HCl space space plus space straight S 2 FeCl subscript 3 space plus space straight H subscript 2 straight S space space space rightwards arrow space space space 2 FeCl subscript 2 space plus space 2 HCl space plus space straight S$