Question

An old cycle frame was left open for a few days. A brown layer got slowly deposited on its surface and could not be removed when rubbed with sand paper. What happened actually?

Answer 1

Hint: Here, we need to understand the question thoroughly in parts to find the solution. As the object referred to in the question is a cycle which was kept in open. So, we know that a cycle is made of steel or iron. And when any brown colour layer forms on a steel or iron surface then it refers to corrosion. So, to answer this question we need to recall the basic concepts of corrosion and rusting.

Complete step by step answer:
Firstly, let’s understand what corrosion is.
Corrosion is a step by step process in which a metal gets destroyed or corroded when it comes in contact with the environment. It is an oxidation-reduction reaction in which the metal gets oxidized by the surrounding elements like oxygen present in the air. With oxygen, temperature, pressure, and chemical salts the cycle gets corroded and a brown layer is formed on the cycle frame in the presence of oxygen and water. The brown layer covering the cycle is known as rusting.
When oxidation Fe becomes
$Fe \to F{e^{3 + }} + 3{e^ - }$
Here, $F{e^{3 + }}$ is the brown colored rust.
Thus, the reaction becomes
$4Fe + 3{O_2} + 2x{H_2}O \to 2F{e_2}{O_3}.x{H_2}O$
Thus, the brown layer cannot be removed with sandpaper. It further impacts the quality and performance of the cycle and leads to structural damage. So, next time to avoid this brown layer paint your cycle regularly as it will create a layer of coating and the cycle will not get corroded or rusted.

Note:
-Stainless steel is more resistant to corrosion.
-Abrasive rubber polishers, abrasive buff wheels, pieces of aluminium foil, baking soda, and vinegar can help to remove rust from a metal surface.