# E cell values and complex ionsWatch

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1. E cell values:
-How do I do complex calculations where there are 3 equations present with cell values?

also, are there any general rules/tips anybody can suggest to help me remember how to arrange the equations (more negative or positive etc.) to calculate the values? I am confused why all the equations are going in one direction when I thought the cathode must be on the right/anode on the left?

Here is the question:
-Use the standard reduction potentials below to explain how fe2+ ions can catalyse the oxidation of iodide ions, I-, by persulphate ions, S2O82-
1. S2O82- (aq) + 2e- --> 2SO42- (aq) Eo = +2.01V
2. I2(s) + 2e- --> 2I- (aq) Eo = +0.54 V
3. Fe3+ (aq) + e- --> Fe2+ (aq) Eo = +0.77 V

-Also how do we suggest an equation where iron (Fe) metal is acting as a catalyst?

2. Ligand exchange
-I just don't get how we know how many ligands are exchanged. For example what would the ligand exchange be between hydrated iron (III) ions and cyanide ions? Would we just guess that 2H2O are replaced or is there a rule?

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