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Question Question 6(iv)
Give reasons
(a) Brass is preferred over copper for door settings.
(b) Metals like iron, aluminium, cobalt and nickel become passive (inert) with concentrated nitric acid.
(c) Alloying of gold is done with silver or copper.
(a) Brass is preferred over copper for door settings as:
- Hardness and tensile strength — Brass is stronger than its components, Copper and Zinc.
- Corrosion resistance — Brass has good corrosion resistance due to the presence of zinc in its composition.
(b) When these metals react with concentrated nitric acid, the nitric acid oxidises the metals, forming metal oxides on their surface. The metal oxides, in turn, form a protective layer preventing further reaction with nitric acid.
(c) As pure gold is very soft so in order to increase its strength such that jewellery could be made, alloying of gold is done with silver or copper.