What's the half equation and the balance overall equation for the reaction in which , a solution containing iron2 ions is oxidised by an acidified solution containing dichromate ions (Cr2O7-2)
Fe^2+ ==> Fe^3+ + e
Cr2O7^2- + 6e + 14H^+ ==> 2Cr^3+ + 7H2O
Multiply equation 1 by 6 and equation 2 by 1. Add them. Then cancel any thing that is common to both sides (that will be the 6 electrons).