Question

(a) Write the chemical name of the coating that forms on silver and copper articles when these
are left exposed to moist air.
(b) Explain what is galvanisation. What purpose is served by it?
(c) Define an alloy. How are alloys prepared? How do the properties of iron change when:
(i) small quantity of carbon,
(ii) nickel and chromium are mixed with it.

Answer 1

(a) On copper, copper carbonate( green ) is formed and on silver, silver sulphide ( black ) is formed.

(b) Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc.

(c) an alloy is a homogeneous mixture of two or more metals or a metal and a nonmetal.

lt is prepared by first melting the primary metal and then dissolving the other metal in it in definite proportion. it is done cool to room temperature.

(i) on mixing carbon to iron it becomes hard and does not stretch easily.

(ii) on mixing it with Nickel and chromium we get stainless steel which is hard and do not rust.