What is rate of corrosion (metals) in HCl, seawater and distilled water?

How does this (corrosion) affect the appearance of the metal?

Can it be explained in detail

1 Answer
Oct 29, 2017

Well the rate should increase in the order: "distilled water;" "seawater;" "hydrochloric acid"....

Explanation:

We interrogate the oxidation reaction for some unspecified metal....

M(s) rarrM^(2+) + 2e^(-)

And for every oxidation, electron loss, there must be a corresponding electron gain....and here the water solvent is reduced....

H_2O(l) + e^(-) rarr 1/2H_2(g) + HO^-

And in the acid we actually supply hydronium ions to be reduced....

H_3O^+ +e^(-) rarr 1/2H_2(g) + H_2O(l)

And to quantify this we draw on redox potentials ....

When E^@ is LESS than ZERO, this means that the oxidation reaction (the reverse of the reduction reaction) is SPONTANEOUS as written....i.e. consider the alkali metals....

Li^(+) + e^(-) rarr Li(s) ;E^@=-3.01*V

Ca^(2+) + 2e^(-) rarr Ca(s) ;E^@=-2.87*V

And since DeltaG^@=-nFE^@, a NEGATIVE value of E^@ signifies a spontaneous reaction FOR the OXIDATION, i.e. for....

Ca(s) rarr Ca^(2+) +2e^(-)...spontaneous as written....