Question

Rusting of an article made up of iron is called:
(A) corrosion and it is a physical as well as a chemical change
(B) dissolution and it is a physical change
(C) corrosion and it is a chemical change
(D) dissolution and it is a chemical change

Answer 1

Hint: Articles made of iron upon exposure to air starts forming a coat in the form of chips which we call rusting of iron. This process is due to the chemical reaction between the iron present on the surface with the oxygen from the atmosphere. This process is irreversible.

Complete step by step solution:
Iron present on the surface of an iron article changes its colour to greenish-brown upon exposure to the atmosphere. Iron gets oxidised into iron(II) oxide under the action of oxygen present in the atmosphere.
The process of rusting of iron is called corrosion. Corrosion is a chemical change as the formation of iron oxide is an irreversible process.

Therefore, the correct answer is option (C).

Additional information:
Galvanization is the process of applying a protective zinc coating to iron, to stop corrosion.
The most common method is hot-dip galvanizing, during which the parts are submerged during a bath of molten hot zinc.
Galvanizing protects the underlying iron or steel in the following main ways:
-The zinc coating, when intact, prevents corrosive substances from reaching the underlying steel or iron.
-The zinc protects iron by corroding first. For better and long-term results, chromates along with zinc are used to galvanize iron.
-In the event the underlying metal becomes exposed, protection can continue as long as there is zinc close enough to be coupled electrically. Once the zinc in the area is consumed local corrosion of the base metal starts.

Note: Although galvanizing will prevent the attack of the base metal ( here, iron), corrosion is an inevitable phenomenon. After years of exposure, the metal will eventually start to corrode. For example, corrugated iron sheets used in roofs will start rusting in a few years. Galvanized iron exposed to the marine environment will start rusting as the zinc metal is converted to soluble zinc chloride which simply washes away.