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) Ag₂S (silver sulphide) is formed on silver, basic copper carbonate CuCO₃. CU(OH)₂ is formed on copper. 

(b) The process of coating zinc over iron is called galvanisation. It is used to prevent rusting of iron. 

(c) Alloy is a homogeneous mixture of two or more metals. One of them can be non-metal. Alloys are prepared by melting two or more metals together. (?) Iron does not rust on adding small,quantity of carbon. (ii) When we form alloy of iron with nickel and chromium, we get stainless steel which is malleable and does not get rusted.