Asked by janice
How does the presence of sodium chloride and acidic substances increase the speed of rusting?
Will alkaline substances increase the speed of rusting?
Will alkaline substances increase the speed of rusting?
Answers
Answered by
GK
In any electrolytic (salt or acid ) solution, electrons are transferred from Fe to O2 in a series of steps. Here is the overall reaction:
2Fe + O2 + 2H2O ---> 2Fe(OH)2
Acid reduces the concentration of OH- ions which drives this reaction faster.
The Fe^+2 ions in Fe(OH)2 are oxidized further to Fe^+3, and the hydroxides are dehydrated to Fe2O3 (rust):
Fe^+3 + 3H2O ⇌ Fe(OH)3 + 3 H+
Fe(OH)3 ⇌ FeO(OH) + H2O
2 FeO(OH) ⇌ Fe2O3 + H2O
Some of the above steps will go faster in the presence of a basic solution. However the loss of electrons by metallic iron which starts the entire sequence will be slower in a basic solution.
2Fe + O2 + 2H2O ---> 2Fe(OH)2
Acid reduces the concentration of OH- ions which drives this reaction faster.
The Fe^+2 ions in Fe(OH)2 are oxidized further to Fe^+3, and the hydroxides are dehydrated to Fe2O3 (rust):
Fe^+3 + 3H2O ⇌ Fe(OH)3 + 3 H+
Fe(OH)3 ⇌ FeO(OH) + H2O
2 FeO(OH) ⇌ Fe2O3 + H2O
Some of the above steps will go faster in the presence of a basic solution. However the loss of electrons by metallic iron which starts the entire sequence will be slower in a basic solution.
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