Question

Explain the following:
(i) Galvanisation protects iron from rusting.
(ii) Stainless steel is more useful than steel.
(iii) Aluminium is extensively used for making aircraft parts.
(iv) Hot water has no action on aluminium.

Answer 1

(a) Galvanisation is a process in which iron is coated with zinc by plunging it into molten zinc, or by electrolysis. Because zinc is more reactive than iron, it reacts first and prevents iron from rusting.

(b) Stainless steel (alloy of Fe, C with Ni and Cr) has high resistance to corrosion and does not rust at all. But steel (alloy of Fe and C) corrodes as it is less resistant to corrosion than stainless steel. Thus, stainless steel is better and more useful than steel.

(c) Aluminium is a light metal and has high resistance to corrosion. But its alloys, namely, duralumin and magnalium are light weight, hard, tough and also resistant to corrosion. Thus, these properties of aluminium and its alloys makes them extensively useful in making aircraft parts.

(d) Aluminium does not react readily with hot water. Red hot aluminium reacts with steam to form aluminium oxide and hydrogen gas.

$$\begin{gathered} 2\mathrm{Al}+3{\mathrm{H}}_2\mathrm{O}\stackrel{}{\to }{\mathrm{Al}}_2{\mathrm{O}}_3+3{\mathrm{H}}_2 \\ \mathrm{Red}\mathrm{hot}\mathrm{Steam}\mathrm{Aluminium}\mathrm{oxide}\mathrm{Hydrogen}\mathrm{g}\mathrm{as} \\ \mathrm{A}\mathrm{luminium} \end{gathered}$$