Question

based on standard reduction potentials which metals would
i) inhibit rusting
ii)promote rusting


My general statement is:
> If the reduction potential is higher it will inhibits rusting and if it is lower it will promote rusting


But im not sure because it doesn't make sense with Mg

Answer 1

For a given reduction potential table, electron flow is from the more negative E-value to the more positive E-value. This would imply metals with a more negative E-value would undergo oxidation and the more positive E-value reduction. So, considering Zn => Zn^+2 + 2e (E = -0.76v) would be the reducing agent for Fe^+3 + 3e => Fe (E = -0.04v). As the Zn is the anode (undergoing oxidation) and the cathode (undergoing reduction) would indicate E-values that are more negative relative to Fe reduction potential (assuming you are referring to Ferric Oxide rust) would inhibit rusting. Such is referred to as 'Cathodic Protection'; that is, one is trying to protect the metal at the cathode by connecting with a more negative E-value metal as the anode. The anode will disintegrate before the metal at the cathode.