Question

4. When an iron post is immersed in water, rust forms at the water line and the iron post pits below the water line. Explain why this happens. (52 Why do aluminum pots and pans develop a pitted surface when table salt is added to the cooking water? e faco of conner which is exposed

Answer 1

4. The formation of rust can only happen if Oxygen is also present in order to form rust via the reaction:

4 Fe + 3 O₂$\rightarrow$ 2 Fe₂O₃

This is why the rust only forms along the water line

5. The reaction between Al and Chloride ions forms the white insoluble salt AlCl₃ which is deposited on the vessel surface.

Al + 3 Cl^-$\rightarrow$ AlCl₃