Write short note on following- Corrosion

Corrosion is a slow process in which metals are eaten up and gradually converted into its undesirable compounds of sulphides, carbonates, oxides etc, by the action of air, moisture present in atmosphere or by an acidic chemical on their surface. For example- Rusting of iron is a redox reaction in which reddish brown coating is formed on iron. Black coating on silver. Green coating on copper. It also weakens the iron or steel structures and objects such as railing, bridges, ships, etc. To prevent this, the processes like oiling, painting, galvanization can be opted. The following chemical reaction can be observed during corrosion- 4 Fe Iron + 3 O 2 Oxygen + 2 xH 2 O Water → 2 Fe 2 O 3 . xH 2 O Hydrated iron III oxide Rust

Those substances which are made by combining two or more metals or a metal and a non-metal and possessing the metallic character or desirable qualities of metals like hardness, lightness and strength is known as an alloy. They form homogeneous mixtures. They are more resistant to corrosion. For example- Steel, Brass, and, bronze. Brass is an alloy of two metals- copper and zinc. Steel or and stainless steel is an alloy of iron and carbon.

Give two differences between metals and non-metals.

Metals and non-metals can be differentiated as follows- Metals Non-Metals Metal reacts with water to liberate hydrogen gas. Non-metals do not react with water. Metals combine with oxygen and form basic oxides. These turns red litmus to blue. 4 Na + O 2 → 2 Na 2 O Non-metals combine with oxygen and form acidic oxides or neutral oxides. These turns blue litmus to red. C + O 2 → CO 2 Eg- Sodium, Potassium. Eg- Carbon, Sulphur.

How many maximum electrons may be in L-shell?

Electronic configuration is defined as the distribution of the electrons in the energy shells (K, L, M, N). According to Bohr-Bury theory, the maximum number of electrons that can be present in energy shells is given by 2 n 2 , where n is the number of energy shells. Therefore, the maximum number of electrons in L-shell is 8 . Electron shell calculation Maximum electrons K shell n = 1 no . of e - = 2 n 2 = 2 × 1 2 = 2 × 1 = 2 2 electrons L shell n = 2 no . of e - = 2 n 2 = 2 × 2 2 = 2 × 4 = 8 8 electrons M shell n = 3 no . of e - = 2 n 2 = 2 × 3 2 = 2 × 9 = 18 18 electrons N shell n = 4 no . of e - = 2 n 2 = 2 × 4 2 = 2 × 16 = 32 32 electrons

Which acids are used in preparation of aqua regia, and what are their proportion? Write one characteristic of Aqua regia.

Aqua-regia is prepared by fresh mixture of concentrated nitric acid and concentrated hydrochloric acid in 3 : 1 ratio respectively. It is highly corrosive, fuming liquid which can dissolve all metals like gold, platinum, etc. Due to its corrosive property, it can be used to clean glassware and refining gold metals.