question_answer

Give reasons for the following : (a) Aluminium finds application as a foil for wrapping food stuffs. (b) Amalgamated sodium is preferred to sodium metal for use in the preparation of hydrogen. (c) Electrical wires made of nichrome are preferred to copper wires for specific applications. (d) Zinc is added to copper in the right proportion for the manufacture of hardware and screws. (e) Flexible pipes are generally made of lead. (f) Aluminium utensils are preferred to copper utensils. (g) Solder is preferred to lead for use in fuse wire.

Answer:

(a) Aluminium does not react with dry air and with moist air. It forms thin oxide layer which renders the metal passive. Hence, it does not react with food stuffs. (b) Reaction of cold water with Na is vigorous, therefore to minimize the rate of reaction sodium amalgam is used in the preparation of hydrogen. (c) Nichrome, an alloy of nickel, iron and chromium is more resistant to electricity, hence, preferred to copper in certain applications. (d) Zinc is added to copper to prepare an alloy of brass which is corrosion resistant and more malleable and ductile. (e) Lead is used in flexible pipes because, (i) it is malleable. (ii) It is bad conductor of electricity (iii) it has high melting point (f) aluminium utensils resist corrosion. (g) Solder has low melting point and it can?t be acted upon air and water. Therefore, preferred in making fuse wire.