+2S2O2−3(aq)++6Cr2O2−7(aq)→+2.5S4O2−6(aq)++3Cr3+(aq)
Cr2O2−7 is oxidising agent.
S2O2−3 is reducing agent.
+2S2O2−3(s)→+2.5S4O2−6(aq) oxidation
nf=(|+2.5−2|×2=1
+6Cr2O2−7(aq)→+3Cr3+(aq) reduction
nf=(|3−6|×2=6
Cross multiplying:
6 S2O2−3(aq)+1 Cr2O2−7(aq)→S4O2−6(aq)+Cr3+(aq)
Balancing elements except O and H
6 S2O2−3(aq)+Cr2O2−7(aq)→3 S4O2−6(aq)+2 Cr3+(aq)
Balancing oxygen atoms by adding H2O
6 S2O2−3(aq)+Cr2O2−7(aq)→3 S4O2−6(aq)+2 Cr3+(aq)+7 H2O
Balancing hydrogen by adding H+
6 S2O2−3(aq)+Cr2O2−7(aq)+14H+→3 S4O2−6(aq)+2 Cr3+(aq)+7H2O
Balancing charge:
charge in reactant side = -12-2+14=0
charge in product side = -6+6=0
so the balanced equation is 6 S2O2−3(aq)+Cr2O2−7(aq)+14H+→3 S4O2−6(aq)+2 Cr3+(aq)+7H2O
The coefficient of H+ in balanced equation is is 14