How to formulate and balance a redox equation under acidic conditions

In a reaction between  MnO4- and Fe2+ we are told MnO4- goes to Mn2+ and Fe2+ goes to Fe3+. We then need to derive the redox equation for the reaction occuring. First we need to idenfity which species are being reduced and which are oxidised. We can use ' OIL RIG' when referring to electrons to help us.OxidationIsLoss of electronsReduction Is Gain of electronsMnO4- (where Mn has a +7 oxidation state) gains electrons, hence is reduced, to Mn2+ and Fe2+ loses electrons, hence oxidised, to Fe3+. Starting with the reduction half equation,    1. Write out the reactant and product                   MnO4-        ------>   Mn2+2. Use H2O to balance the oxygen                    MnO4-        ------>   Mn2+ + 4H2O3. Use H+ (as under acidic conditions) to thenbalance the other side of the equation                  MnO4- + 8H+        ------>   Mn2+ + 4H2​O4. Add electrons to balance the charges                MnO4- + 8H+ + 5e-    ------>   Mn2+ + 4H2​OFor the oxidation half equation,1. Write out the reactant and product                  Fe2+   ------->   Fe3+2. Balance the equation using electrons                Fe2+ ------->   Fe3+ + e-To combine the reduction and oxidation half equations we need to have the same number of electrons. Multiply the oxidation half equation by 5 to give us 5Fe2+  ------->   5Fe3+ + 5e-Then add the two half equations together, canceling any like terms (the electrons) from both sides. The overall redox equation is therefore 5Fe2+ + MnO4- + 8H+   ------>  5Fe3+ + Mn2+ + 4H2​O 

Answered by Kiera D. Chemistry tutor

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