Some Important Chemical Compounds

Introduction

     Sodium belongs to Group I in the periodic table. This group is otherwise known as the alkali metals group. Since the atomic number of sodium is 11, its electronic configuration is 2,8,1. Sodium easily loses the lone electron to attain the stable configuration of neon. Therefore alkali metals like sodium that are univalent can easily form ionic compounds. Sodium bicarbonate (NaHCO₃) is an example for the univalent nature of sodium.

Sodium Carbonate

     Popularly known as washing soda or soda ash, sodium carbonate is a commercially important compound. In earlier days, it was obtained from the ash of plants and from natural deposits in India and Egypt.

Sodium Bicarbonate

     Sodium bicarbonate is commonly called baking soda.
     Manufacture of Sodium Bicarbonate
     Sodium bicarbonate is obtained as an intermediate product in the Solvay's process, as detailed earlier.

Bleaching Powder

     Calcium oxychloride is the chemical name of bleaching powder.
     Preparation of Bleaching Powder
     Passing chlorine gas over dry slaked lime (Ca(OH)₂), gives bleaching powder.
     

Plaster of Paris

     Chemically, plaster of paris is known as calcium sulphate hemihydrate (hemi means half).
     Plaster of Paris is prepared from gypsum (calcium sulphate dihydrate, CaSO₄.2H₂O).

Cement

     Portland cement is a very important building material. It was first discovered in England. It got its name because on setting, it hardened to a stone-like mass and was compared to the famous Portland Rock of England. It is a mixture of calcium and aluminium silicates with gypsum.

Glass

     Any amorphous and transparent solid that is a product of the solidification of a liquid is called glass. However, glass is generally referred to as the transparent substance obtained when white sand is fused with oxides and carbonates of alkaline earth metals and the molten mixture is cooled. Glass is a super cooled liquid i.e., it is a liquid cooled much below its freezing point. The ordinary room temperature is much below the freezing point of glass.

Steel

     Carbon content of steel is between 0.1 and 1.5%. This is intermediate between cast iron and wrought iron. The hardness of steel increases with increase in carbon content. Steel contains other elements like manganese, chromium, silicon, nickel, tungsten, vanadium, and molybdenum. These elements are added for making steels of different kinds.

The Open Hearth Process

     A mixture of cast iron, scrap iron, iron ore (haematite) and lime is melted in an Open Hearth Furnace. The hearth is lined with silica (SiO₂) or calcined dolomite (CaO.MgO) based on whether the impurities present in cast iron. If the impurities are manganese and silicon, silica lining is used. Calcined dolomite lining is used if much of phosphorus is present. Producer gas (a mixture of carbon monoxide and nitrogen) is burned to heat the furnace to 1500^oC. Fuel is saved by regenerative heat economy method, by using a set of heat regenerators, made of brick checker work.

The Electric Furnace Process

     In this process, heating is done with the help of a carbon arc. The electrodes are held vertically and the charge (cast iron, scrap iron and iron ore) and lime mixture, is held in between. The furnace is lined with dolomite.

Cementation Process

     Numerous bars of wrought iron surrounded by carbon are heated in fire-brick boxes to a temperature of around 1000^oC for 10 days. The carbon diffused slowly into iron and converts iron into steel. Carbonisation of the iron bars is obviously more at the surface. This results in blisters and the steel is known as blister steel.

Properties of Steel

     The properties of steel depend on the carbon content and the heat treatment imparted to it. If the carbon content is low, the steel is soft and ductile and is called mild steel.

Calcium Oxide (CaO)

     Calcium oxide is commonly called Quick Lime. Quick lime has always been a cheap commodity because limestone deposits are readily available. Lime manufacturing and application dates back to the Roman, Greek and Egyptian civilizations.

Slaked Lime

     When calcium oxide reacts with water, it liberates heat and cracks into a white powder. This white powder is calcium hydroxide or slaked lime. The process is called slaking of lime.
     

Summary