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Chapter: 12th Chemistry : p-Block Elements-II

p-Block Elements-II: Summary

About 78 % of earth atmosphere contains dinitorgen (N2) gas. It is also present in earth crust as sodium nitrate (Chile saltpetre) and potassium nitrates (Indian saltpetre).

Summary

Occurrence: About 78 % of earth atmosphere contains dinitorgen (N2) gas. It is also present in earth crust as sodium nitrate (Chile saltpetre) and potassium nitrates (Indian saltpetre).

Nitrogen, the principle gas of atmosphere (78 % by volume) is separated industrially from liquid air by fractional distillation

Ammonia is formed by the hydrolysis of urea.

Nitric acid is prepared by heating equal amounts of potassium or sodium nitrate with concentrated sulphuric acid.

In most of the reactions, nitric acid acts as an oxidising agent. Hence the oxidation state changes from +5 to a lower one. It doesn’t yield hydrogen in its reaction with metals.

The reactions of metals with nitric acid are explained in 3 steps as follows:

Primary reaction: Metal nitrate is formed with the release of nascent hydrogen

Secondary reaction: Nascent hydrogen produces the reduction products of nitric acid.

Tertiary reaction: The secondary products either decompose or react to give final products

Phosphorus has several allotropic modification of which the three forms namely white, red and black phosphorus are most common.

yellow phosphorus is poisonous in nature and has a characteristic garlic smell. It glows in the dark due to oxidation which is called phosphorescence.

Yellow phosphorus readily catches fire in air giving dense white fumes of phosphorus pentoxide.

Phosphine is prepared by action of sodium hydroxide with white phosphorous in an inert atmosphere of carbon dioxide or hydrogen.

Phosphine is used for producing smoke screen as it gives large smoke.

When a slow stream of chlorine is passed over white phosphorous, phosphorous trichloride is formed.

phosphorus trichloride: and Phosphorous pentachloride are used as a chlorinating agent

Oxygen is paramagnetic. It exists in two allotropic forms namely dioxygen (O2) and ozone or trioxygen (O3).

Ozone is commonly used for oxidation of organic compounds.

Sulphur exists in crystalline as well as amorphous allotrophic forms. The crystalline form includes rhombic sulphur (α sulphur) and monoclinic sulphur (β sulphur). Amorphous allotropic form includes plastic sulphur (γ sulphur), milk of sulphur and colloidal sulphur.

Sulphuric acid can be manufactured by lead chamber process, cascade process or contact process.

When dissolved in water, it forms mono (H2SO4.H2O) and dihydrates (H2SO4.2H2O) and the reaction is exothermic.

Halogens are present in combined form as they are highly reactive.

Chlorine is manufactured by the electrolysis of brine in electrolytic process or by oxidation of HCl by air in Deacon’s process.

Chlorine is a strong oxidising and bleaching agent because of the nascent oxygen.

When three parts of concentrated hydrochloric acid and one part of concentrated nitric acid are mixed, Aquaregia (Royal water) is obtained. This is used for dissolving gold, platinum etc...

Hydrogen halides are extremely soluble in water due to the ionisation.

Each halogen combines with other halogens to form a series of compounds called inter halogen compounds.

Fluorine reacts readily with oxygen and forms difluorine oxide (F2O) and difluorine dioxide (F2O2) where it has a -1 oxidation state.

All the noble gases occur in the atmosphere.

They are extremely stable and have a small tendency to gain or lose electrons. Sodium per xenate is very much known for its strong oxidizing property.

The inertness of noble gases is an important feature of their practical uses.

 

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