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 galvanization. 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 is mixed?

(ii) nickel and chromium are mixed with it?

Answer 1

(a) Silver sulphide, copper carbonate coating is formed on Ag & Cu article.

(b) Galvanization is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc. The galvanized article is protected against rusting even if the zinc coating is broken.

(c) Alloy is a homogeneous mixture of two or more metals and non-metals. It is prepared by first melting the primary metal and then dissolving the other elements in it in definite proportion. It ii then cooled at room temperature.

(i) On mixing carbons, it becomes hard and strong,

(ii) On mixing Ni and Cr, it becomes hard and does not rust.