Question

(a) How does the painting of an iron object prevent its rusting?
(b) How does the electrical conductivity of copper alloys, brass and bronze, differ from that of pure copper?
(c) What is meant by 22 carat gold? Name the metals which are usually alloyed with gold to make it harder.

Answer 1

(a) The regular method used to prevent rusting of iron objects is painting the surfaces of iron objects. Rusting takes place in the presence of both air and water. Thus, when a layer of paint is applied to the surface of an iron object, it prevents the contact of air and moisture with the iron surface and avoids the rusting of iron objects.

(b) Alloys of copper, brass (alloy of copper and zinc) and bronze (alloy of copper and tin) are very poor conductors of electricity. However, copper is an excellent conductor of electricity; therefore, it is used in electrical wiring.

(c) An alloy of gold with copper or silver (Cu and Ag are mixed with gold to make it harder) is called 22 carat gold. The value refers to 22 parts of pure gold alloyed with two parts of either silver or copper. 22 carat gold is used for making jewellery.