Determine the oxidation states of Se and S in the products and reactants of the following equation. Amongst the reactants, which species would be called the oxidant and which would be called the reductant?
0.5 SeO4^2- (aq) + 0.125 H2S (aq) = 0.5 SeO3^2- (aq) + 0.125 SO4^2- (aq) + 0.25 H+ (aq)
1. compounds must have zero charge.
2. ions must have charge on the ion.
3. oxidation states in the compound/ion must add to the charge.
For SeO4^2-, youhave
O is -2 and 4*-2 = -8 so Se must be +6 t leave a charge of -2 on the ion.
For H2S, H is +1, 2*+1 = +2 so S must be -2. The right hand side is done the same way.
The oxidizing agent (oxidant) is the one that gained electrons.