Question

(a) What is corrosion?
(b) Name any two metals which do not corrode easily.
(c) What is the corrosion of iron known as?
(d) Explain why, aluminium is a highly reactive metal, still it is used to make utensils for cooking.

Answer 1

(a) Corrosion is the damage caused to the metal by the chemical reaction of air, water and acids with the surface of the metal. Generally reactive metals corrode easily and non-reactive metals have good resistance to corrosion.

(b) Gold and platinum are two metals that do not corrode easily. These two metal are highly non-reactive; therefore, they have a very high resistance to corrosion.

(c) The corrosion of iron is known as rusting. Iron is a reactive metal and corrodes (rusts) in the presence of air (oxygen) and water (dampness).

(d) Aluminium is a highly reactive metal. It reacts easily with oxygen in the air and forms layer of aluminium oxide on its surface. This aluminium oxide layer is very tough and does not allow the air to enter the metal for further reaction. This prevents further corrosion of aluminium. Therefore, aluminium articles become unreactive towards air and water and do not corrode easily due to the presence of strong aluminium oxide layer over them. This oxide layer on aluminium is made further strong by making it thick by a process called anodising. This prevents corrosion to the maximum. Hence, aluminium becomes highly resistive to corrosion and it is used to make utensils for cooking.