Q5Engineering Chemistry
Question
2 marks
Under identical conditions why does impure metal corrode faster than pure metal?
Answer
Impure metals corrode faster because the impurities act as cathodes, setting up numerous local galvanic cells that accelerate the oxidation of the anodic base metal.
When a metal contains impurities (which are usually more noble or less reactive), the impurities and the base metal create microscopic galvanic cells when exposed to an electrolyte (like moisture).
The pure metal acts as the anode and gets continuously oxidized (corroded), while the impurity acts as the cathode. In completely pure metals, such local electrochemical cells cannot form, making them much more resistant to corrosion.