Question

Why is iron nail always rubbed with sandpaper before being used in any chemical experiment?

Answer 1

1. Corrosion is wasting away of metals layer by layer in the presence of air and moisture.
2. Iron nails when exposed to air and moisture it gets corroded away and a layer of Oxide is formed on their surface.
3. The chemical reaction for the following could be written as:
4. $Fe\left(s\right)+O_2\left(g\right)+x.H_{2}O\to \underset{\left(Rust\right)}{\underbrace{F{e}_2{O}_3.x{H}_{2}O\left(s\right)}}$
5. Rusting changes the appearance of the iron, the shiny luster goes away and surface appears dull reddish brown.
6. And also the surface is now hindered with oxide layer which is not suitable for the chemical reaction.
7. So, before any chemical reaction iron nails were always rubbed with sandpaper so that the oxide layer could be wiped off.