Alloys can be defined as the homogenous mixture of two or more metals or non metals. Alloying of metals is done to improve the properties of metals such as their hardness, toughness, brittleness, colour and their durability. Here we will discuss some important alloys of steel and their various uses.

1. Stainless Steel

Stainless steel is an alloy of iron, chromium and nickel. The percentage composition of nickel and chromium in stainless steel is 18 %. Stainless steel is resistant to corrosion i.e. it cannot get corroded by the action of water, oxygen gas or any other chemical. That is why it is used for making utensils, knives, scissors, tools, and surgical instruments. It is also used for making tools and equipments for food processing industry and dairy industry.

2. Tungsten Steel

Tungsten steel contains about 15 to 20 % of tungsten, 5% of chromium and a little of vanadium. It has the ability to retain its hardness even at high temperature. It is used for making drilling tools and cutting tools for high speed lathes.

3. Silicon Steel 

 Silicon steel contains about 15 % of silicon. It is very hard and resistant to acids. It is used for making pumps and pipes for carrying acids. Silicon steel containing up to 35 % of silicon is used for making transformers and electromagnets.

4. Cobalt Steel

Cobalt steel contains about 35 % of cobalt. It has a very good magnetic property that is why it is used for making permanent magnets.

5. Manganese Steel

Manganese steel contains about 7 to 20 % of manganese. It is very hard, tough and resistant to wear and tear. It is used for making steel helmets, rock crushing machinery and burglar proof safes.

6. Nickel Steel

Nickel steel contains about 3.5 % of nickel. It is very hard, elastic and resistant to corrosion. It is used for making bicycle parts and aeroplanes parts like wire cables, gears, drive shafts, and propeller shafts.

7. Chromium Steel

Chromium steel contains about 2 to 4 % of chromium. It has high tensile strength. It is used for making ball bearings, cutting tools and cutlery.

Test your understanding and answer these questions:

1. Explain different types of alloys of steel.

Steel is an alloy of iron and carbon. It is prepared by mixing about 0.1 % to 1.5 % of carbon in iron.

Methods of Production of Steel

 Steel can be manufactured by using following three methods.

• Bessemer converter
• Open hearth process
• Electric furnace process

But here we will discuss only one method of preparation of steel by using Bessemer converter.

Production of Steel

The raw material used for the production of steel is pig iron or cast iron which contains carbon, Sulphur, manganese, silicon and phosphorous as impurities. Steel is prepared in a pear shaped furnace called as Bessemer converter. Bessemer converter is a specially made furnace which has holes at its bottom through which hot air can be passed into it. The Bessemer converter can also be rotated or tilted in any direction around its axis.

We will now discuss the procedure of production of steel. First of all molten pig iron is put into the Bessemer converter by tilting it sidewise. Some calcium oxide is also put into it which helps in the removal of phosphorus impurities present in the pig iron. Bessemer converter is now brought back into the vertical position and a blast of hot air passed into the Bessemer converter through the holes at its bottom. The oxygen present in the hot air oxidizes the various impurities present the pig iron as follows:

Carbon present as impurity in pig iron is oxidized by the oxygen of hot air to carbon monoxide gas.

2C          +          O₂                     2CO

Carbon           Oxygen                                      Carbon monoxide

This carbon monoxide gas burns at the mouth of the Bessemer converter to form carbon dioxide gas.

2CO                  +           O₂                     2CO₂

Carbon monoxide     Oxygen                                        Carbon dioxide

Sulphur present as impurity in pig iron is oxidized by the oxygen of hot air to Sulphur dioxide gas which escapes from the Bessemer converter.

S          +           O₂                     SO₂

Sulphur        Oxygen                                        Sulphur dioxide

Manganese present as impurity in pig iron is oxidized by the oxygen of hot air to form manganese oxide.

     2Mn        +        O₂                     2MnO

Manganese         Oxygen                                        Manganese oxide

Silicon present in the pig iron is oxidized into silicon dioxide.

    Si        +        O₂                     SiO₂

 Silicon           Oxygen                                          Silicon dioxide

Manganese oxide and silicon dioxide react together to form manganese silicate slag.

MnO        +        SiO₂                  MnSiO₃

     Manganese oxide     Silicon dioxide                         Manganese silicate (slag)

Phosphorous present as impurity in pig iron is oxidized by the oxygen of hot air to form phosphorous pentaoxide.

     4P            +           5O₂                  2P₂O₅

phosphorous        Oxygen                                Phosphorous pentaoxide

This phosphorous pentaoxide reacts with calcium oxide which is added to the Bessemer converter to form calcium phosphate slag.

3CaO          +           P₂O₅                   Ca₃ (PO₄)₂

Calcium oxide    Phosphorous pentaoxide              Calcium phosphate (slag)

The slag of magnesium silicate and calcium phosphate formed in the above reacts are light in weight, so these float on the surface of molten iron. The slag in the Bessemer converter can be removed by tilting it to one side.

Properties of Steel

       As we have already studied that steel is an alloy of iron with carbon. So its properties depend upon the amount of carbon present in the steel. On the basis of amount of carbon in the steel, it can be categories into following two types:

1. Mild Steel

Mild steel is the most common type of steel. It is prepared by mixing 0.1 % to o.4 % of carbon in iron. Mild steel is quite malleable, ductile and elastic. It is tough and not brittle.

Uses:- It is used for making sheets, wires, chains, car bodies, axles, railway lines, wheels, nails, springs, ships, bridges, girders, pipes, cables, and for construction purposes in buildings.

2. Hard Steel

Hard steel is very hard and brittle. It is prepared by mixing 0.5 % to 1.5 % of carbon in iron.

Uses:- It is used for making cutting tools, chisels, razor blades, knives and drill bits

Quenching, Tempering and Annealing of Steel

The processes of quenching, tempering and annealing of steel are done to modify the hardness and brittleness of steel.

Quenching of Steel

The process in which the steel is heated to red heat (850⁰ C), and then cooled suddenly by putting into cold water is called quenching of steel. By this process steel becomes very hard and brittle.

Tempering of Steel

The process of heating quenched steel or hardened steel to a temperature ranging between 200⁰ C to 350⁰ C, and then cooling it slowly, is called tempering of steel. Tempering of steel is done to prepare elastic, less hard and less brittle steel.

Annealing of Steel

The process of annealing of steel is just opposite to that of quenching of steel. The process of heating steel to red heat and then cooling down slowly is called annealing of steel. Annealing of steel is done to make soft steel.

Test your understanding and answer these questions:

1. What is steel?
2. How steel is manufactured?
3. What do you understand by quenching, annealing and tempering of steel?

We know that glass is used for making many articles, but we cannot use same type of glass for making everything. This means that we need different types of glass for different purposes. These types of glass can be made by changing the chemical composition of ordinary glass.

Now we will study different types of glass, their chemical composition and there uses.

1. Soda Glass or Soft Glass or Ordinary Glass

Soda glass is the cheapest and most commonly used glass. It is made by fusing a mixture of sodium carbonate, calcium carbonate and silica. It is called soda glass because it is prepared from soda ash or sodium carbonate. It is called soft glass because it becomes soft after heating.

Uses:- Soda glass is used for making glass tumblers, mirrors, window panes, electric bulbs, bottles, and dishes etc.

2. Potash Glass or Hard Glass

It is prepared by fusing a mixture of potassium carbonate, calcium carbonate and silica. As its name indicates it is very hard and have high melting point. It is also more resistant to action of acids.

Uses:- Hard glass is used for making hard glass laboratory apparatus.

3. Optical Glass

It is prepared by fusing potassium carbonate, lead oxide and silica.

Uses:- It is used for making lenses which are used in spectacles, cameras, microscopes, telescopes and other optical instruments. It is also used for making glass prisms.

4. Pyrex Glass or Borosilicate Glass

It is made by fusing a mixture of sodium carbonate, potassium carbonate, calcium carbonate, silica, borax and aluminium oxide.

Uses:- It is used for making laboratory apparatus such as flasks, and beakers because it can withstand high temperature while heating without breaking. It is also used for making ampoules which are used for storing the medicines for injections. In our homes the utensils which are used in microwave ovens are made up of Pyrex glass.

5. Safety Glass

It is prepared by sandwiching a thin sheet of plastic between two layers of glass by applying suitable adhesive on both the sides. These three layers are then joined together by the action of pressure and heat to form a single sheet of safety glass. This glass is very strong. It cannot be broken into small pieces by hitting with heavy objects. That is why it is called safety glass.

Uses:- It is used mainly for making the windscreens of automobiles, trains and aeroplanes. It is also used for making bullet-proof jackets.

6. Photo Chromatic Glass

This glass has a unique property of becoming dark coloured when exposed to bright sunlight and coming back to original state when bright sunlight is removed. This happens due to the presence of a layer of silver bromide over it.

Uses:- This glass is used for making spectacles, cameras and goggles.

7. Lead Crystal Glass

It is made by fusing a mixture of potassium carbonate, lead oxide and silica.

Uses:- This glass has the property of shining so it is used for making expensive glass products.

8. Coloured Glass

Coloured glass is made by mixing small amount of colouring materials such as certain metal oxides during the preparation of glass. For example

S No.	Name of the metal oxide	Colour imparted to the glass
1.	Iron oxide	Brown
2.	Cobalt oxide	Blue
3.	Copper oxide	Red

Glass Fibers

Glass fibers are fibers which are used in various applications in industries. These are obtained by forcing molten glass through very fine holes under high pressure. It is used in two forms:

1. Glass wool

Glass wool is a mass of loose glass fibers. Glass wool is an excellent insulator that is why it is used as an insulation material in refrigerators, electric ovens etc. Glass wool is also used for making fire proofing clothing.

2. Optical Fibers

The optical fibers are thin and long glass fibers which transmit signals in the form of light through the process of total internal reflection. These days’ optical fibers are being used extensively in examining the internal parts of human body by a technique called as ‘endoscopy’. These also help in conducting surgical operations. Optical fibers are also being used in telecommunication like telephones.

Test your understanding and answer these questions:

1. What are different types of glass? Explain.
2. What is soda glass? give its use.
3. What is potash glass? give its use.
4. What is pyrex glass? give its use.
5. What is optical glass? give its use.

Glass is a very important chemical compound which is used by humans on a large scale. Today it has acquired such an important place in our daily life that we cannot think to live without it. Many things which we use in our daily life are made up of glass. For example, tumblers, tube lights, plates, electric bulbs, spectacles, laboratory equipments, milk bottles, slides, mirrors, screens of aeroplanes and automobiles are made up of glass. In India it is manufactured in Bangalore, Vadodara, Mumbai, Kolkata, Ferozabad and Delhi.

Chemical Composition of Glass

Ordinary glass which is also known as soda glass or soft glass is a mixture of sodium silicate (Na₂SiO₃), calcium silicate (CaSiO₃), and silica (SiO₂), and its chemical composition is normally represented as Na₂SiO₃.CaSiO₃.4SiO₂ or Na₂O.CaO.6SiO₂.

Raw Materials for Formation of Glass

       Following three substances are required for the manufacture of glass:

• Sodium carbonate
• Calcium carbonate
• Silica

Manufacture of Glass

To manufacture Glass first of all sodium carbonate, calcium carbonate and silica are ground into powder and mixed thoroughly. The homogenous mixture of sodium carbonate, calcium carbonate and silica is called batch. Then a few pieces of broken glass which are called ‘cullet’ are added into the batch. The purpose of adding the cullet in the batch is to lower the melting point of batch because the cullet have low melting point. Thus the addition of cullet into batch helps in early melting of batch during the manufacture of glass. Then a temperature of about 1673 K is produced in the furnace by burning fuel gases. At this high temperature the batch melts and its various components react with each other to form molten glass.

Chemical Reactions Involved in the Formation of Glass

Following are the chemical reactions which takes place during the formation of glass:

1. First of all silica reacts with sodium carbonate to form sodium silicate.
2. In the second step silica reacts with calcium carbonate to form calcium silicate.
   
3. In third step sodium silicate and calcium silicate formed above mixes with silica to form glass.
   

 

The glass formed here is in molten state, so it can be given any shape by cooling it in the moulds of desired shape and size.

Annealing of glass

As we have already studied that different glass articles are prepared by cooling the hot molten glass in moulds. Special care is taken while cooling the hot glass because if it is cooled at once, it becomes brittle and cracks easily and if it is cooled very slowly then it becomes opaque. To avoid the brittleness of glass articles there annealing is done. Annealing is the process in which a glass article is cooled slowly and uniformly.

Test your understanding and answer these questions:

1. What is annealing of glass?
2. What raw materials are used for manufacture of glass?
3. How is glass manufactured?

Cement is the most important building construction material. It has the property of setting into hard mass after mixing with water in required amount. It is also known as Portland cement because after setting into hard mass it resembles with the rocks found in Portland in United Kingdom. It is fine grey powder which is made from limestone and clay.

The chemical formula of cement is CaO.Al₂O₃.Fe₂O₃

Raw Material Required for Manufacturing of Cement

       The two important raw materials used for the preparation of cement are:

1. Limestone

The chemical formula of limestone is CaCO₃ and it is used in the manufacture of cement just to provide CaO.

2. Clay

Clay is hydrated aluminium silicate and iron (iii) oxide having chemical formula Al₂O₃SiO₂Fe₂O₃.2H₂O. Thus clay consists of aluminium oxide (Al₂O₃), silicon dioxide (SiO₂), and iron (iii) oxide (Fe₂O₃) along with water molecules.

In addition of limestone and clay one more substance which is also used during preparation of cement is gypsum which is added into the cement to slow down the initial setting (hardening) of cement when water is added into it.

Chemical Composition of Cement

The %age composition of different compounds present in cement is:

S No.	Compound Name	%age composition
1.	Calcium oxide (CaO)	60-70 %
2.	Silicon dioxide (SiO2)	20-25%
3.	Aluminium oxide (Al2O3)	5-10%
4.	Iron oxide (Fe2O3)	2-3%

Manufacture of Cement

To manufacture cement first of all limestone is added into the clay in proportion of 3:1 by weight. This mixture of limestone and clay is then dried and crushed to get a fine powder called ‘raw meal’. The raw meal is then added into a rotary kiln through a hopper as shown in figure. The rotary kiln is actually a long kiln which is capable to rotate on its axis. It is kept slightly inclined downward so that when it rotates, the raw meal present in it slowly moves downward to the other end of the rotary kiln.

Then a very high temperature of about 1773 K is produced in the rotary kiln by passing hot gases in the rotary kiln from the bottom. At this high temperature limestone reacts with clay to form small pieces of cement called ‘clinkers’.

The clinkers are then cooled down and a small amount of gypsum is added into it. This mixture of clinkers and gypsum is then ground into a fine powder which is called cement. The whole process of preparation of cement can be represented with the help of a simple equation as given below:

    Limestone    +    Clay    +    Gypsum            Cement

Chemical Reactions Involved in the Manufacture of Cement

Following chemical reactions take place during the manufacture of cement:

1. First of all limestone decomposes into lime after getting heated to a high temperature.

2. The lime produced in first reaction reacts with silicon dioxide to produce dicalcium silicate.

3. Lime also reacts with silicon dioxide to produce one more compound tricalcium silicate.

4. Lime also reacts with aluminum oxide to form tricalcium aluminate.

5. In the last step calcium oxide, aluminium oxide and ferric oxide react together to form cement.

Purpose of Adding Gypsum to Cement

As we have already studied that the main purpose of adding gypsum in the cement is to slow down its initial setting when water is added into it. The slow setting of cement helps us to work conveniently and it also leads to more hardening of cement.

Test your understanding and answer these questions:

1. Explain the process of manufacture of cement.

Cement is the most important building construction material. It has the property of setting into hard mass after mixing with water in required amount. It is also known as Portland cement because after setting into hard mass it resembles with the rocks found in Portland in United Kingdom. It is fine grey powder which is made from limestone and clay.

The major cement producing countries in the world are China, Japan, United States of America and India. The main cement producing plants in our country are in Gujarat, Rajasthan, Orissa, Madhya Pradesh, and Tamil Nadu. The production of cement in our country started in 1904 at Chennai in Tamil Nadu.

The chemical formula of cement is CaO.Al₂O₃.Fe₂O₃

Uses of Cement

Cement is used in different forms such as mortar, concrete and reinforced concrete cement (RCC).

1. Mortar

A mixture of cement, sand and water is called mortar. It is prepared by mixing 1 part of cement with 3 parts of sand and then adding the required amount of water. It has the capacity to set into hard mass after sometime that is why it is used for binding the bricks and stones and for plastering of walls and roofs of buildings.

2. Concrete

A mixture of cement, gravel, coarse sand and water is called concrete. It becomes very hard on setting that is why it is used for making roofs, floors, pavements, roads and bridges etc.

3. Reinforced Concrete Cement (RCC)

Reinforce means to make stronger. Concrete can be made stronger by putting a framework of iron or steel inside it. Thus we can define the reinforced concrete cement as the concrete which is made stronger by putting iron or steel framework inside it. The RCC possesses a great strength that is why it is used for making of pillars and roofs of buildings, dams, tunnels, bridges, pipes of water supply and sewage pipes etc.

Test your understanding and answer these questions:

1. What is chemical formula of cement?
2. What is mortar?
3. What is reinforced concrete cement?

Quicklime is the compound which is used commonly for whitewashing houses. The chemical name of quick lime or lime is calcium oxide. The chemical formula of quicklime is CaO.

Manufacture of Quicklime

The raw material used for the manufacture of quicklime is calcium carbonate (CaCO₃). Lime is manufactured by heating the calcium carbonate to a temperature of 1273 K in a lime kiln. After getting heated to such a high temperature calcium carbonate decomposes into lime and carbon dioxide gas. The carbon dioxide gas produced escapes from the lime kiln leaving behind lime.

The diagram of the lime kiln used for the decomposition of calcium carbonate is shown in figure to manufacture lime calcium carbonate is fed into the lime kiln through the hopper situated at the upper end of the lime kiln. The calcium carbonate in the lime kiln is then heated by passing in hot air from the sides of the lime kiln, due to which calcium carbonate decomposes into lime and carbon dioxide. The lime produced is then collected at the bottom of the lime kiln and carbon dioxide produced during the decomposition of calcium carbonate is allowed to escape from the lime kiln.

Properties of Lime

1. Lime is a white solid having very high melting point of 2273 K.
2. When lime is heated in oxy-hydrogen flame, it produces brilliant white light called ‘lime light’.
3. When lime is added in water then it produces a hissing sound and forms slaked lime. This reaction is exothermic in nature.
4. Slaking of Lime:- When lime is added into water then a sound of hissing is produced along with heat and it cracks to form a white powder. This white powder is actually calcium hydroxide which is also called slaked lime.
5. Lime is very stable which means that it doesn’t decompose easily even at high temperatures.
6. Lime can react with moist hydrogen chloride gas to form calcium chloride.

 

Uses of Lime

1. Lime is used in white washing the buildings and houses.
2. It is used in manufacture of many other important compounds such as glass, cement, calcium chloride and calcium nitrate.
3. It is used in the extraction of iron from its ore haematite.
4. It is used as drying agent for drying gases and alcohol.
5. It is also used in tanning industry.
6. It is also used in manufacture of sodium carbonate, bleaching powder and calcium carbide.
7. It is used as a basic lining in furnaces.

Test your understanding and answer these questions:

1. What is chemical name and formula of quick lime?
2. How quicklime is manufactured?
3. What are uses of quick lime?

Plaster of Paris is a white powder which is used mainly for making toys, statues, blackboard chalk and for beautification of ceilings of buildings and houses. It is also used for the setting of fractured bones in the right position. It has got its name from the fact that it was first of all prepared from gypsum which was mainly found in Paris. In short it is also called as P.O.P.

Chemical name and Chemical Formula

The chemical name of plaster of Paris is calcium sulphate hemihydrate because half molecule of water is attached with calcium sulphate. The chemical formula of plaster of Paris is CaSO₄.1/2H₂O.

Preparation of Plaster of Paris

Plaster of Paris is prepared by heating gypsum (CaSO₄.2H₂O) to a temperature of 373 K in a kiln. Actually the chemical name of gypsum is calcium sulphate dihydrate which means that the molecule of gypsum is in fact molecule of calcium sulphate which contains two molecules of water of crystallization. So when gypsum is heated then it loses one and half molecules of water of crystallization leaving only half molecule of water of crystallization remaining attached with calcium sulphate.

During this process care should be taken not to heat the gypsum above 373K because if gypsum is heated beyond the temperature 373 K then all the water of crystallization is removed from it which results in anhydrous calcium sulphate which is also called as dead burnt plaster. The disadvantage of this dead burnt plaster is that it doesn’t set like plaster of Paris after adding in water.

Properties of Plaster of Paris

1. Plaster of Paris is a white powder.
2. It has a property of setting into hard mass when water is added into it, within half an hour. The setting of plaster of Paris is due to its hydration to form crystals of gypsum which set to form hard and solid mass.

 

Uses of Plaster of Paris

1. Plaster of Paris is used in hospitals for setting the fractured bones into right position because of its property of setting into hard mass after adding water into it. This way it helps in rapid and correct healing of fractured bones.
2. It is used for making toys, cheap ornaments, cosmetics, black-board chalk, decorative materials and casts for statues.
3. It is used by dentists for making casts of denture.
4. It is used in chemistry laboratories for sealing air-gaps in apparatus where air tight arrangement is required.
5. It is used for making walls of homes smooth before painting them and for making beautiful designs on the ceilings of houses and other buildings.
6. It is also used as a fire proofing material.

Test your understanding and answer these questions:

1. What is plaster of paris? What is its chemical formula?
2. How is plaster of paris manufactured?
3. What are uses of plaster of paris?

Bleaching powder is very useful chemical compound which is used extensively for bleaching of clothes. It chemical formula is CaOCl₂ and its chemical name is calcium oxychloride.

Manufacture of Bleaching Powder

Bleaching powder in manufactured by passing chlorine gas over dry slaked lime.

Bleaching powder can be manufactured by using two different types of manufacturing plants.

1. Hasenclever plant and

 

1. Bachmann plant.

 

But we will discuss only the manufacturing of bleaching powder by using Hasenclever plant.

Construction of Hasenclever Plant

The Hasenclever plant consists of a number of hollow horizontal cylinders of iron which are fitted with shafts having a large number of blades fixed along entire length which can be rotated inside the cylinders. The uppermost cylinder has a hopper for putting in slaked lime and an outlet for the waste gases to go out. The lowermost cylinder has an inlet for passing in chlorine gas and an outlet for the bleaching powder to come out.

Working of Hasenclever Plant

First of all dry slaked lime is entered into the Hasenclever plant through hopper. Then this dry slaked lime is moved forward by the revolving blades of the rotating shaft. In the meantime chlorine gas is passed through the lowermost cylinder which moves up to the upper cylinders and reacts with the dry slaked lime coming downward to form bleaching powder. This bleaching powder comes out through the outlet at the bottom of innermost cylinder and collected in a vessel.

Properties of Bleaching Powder

1. Bleaching powder is a yellowish white powder with characteristic strong smell of chlorine.
2. It is soluble in water.
3. Reaction with carbon dioxide:- When bleaching powder is exposed in air then it reacts with carbon dioxide gas present in air to produce calcium carbonate and chlorine gas:

   

4. Available Chlorine:- The amount of chlorine which is liberated during reaction of bleaching powder with carbon dioxide or sulphuric acid or hydrochloric acid is called available chlorine. The superiority of bleaching powder can be estimated by the amount of bleaching powder. The greater the amount of available chlorine, more superior will the bleaching powder is. A good sample of bleaching powder contains 35 to 38 % of available chlorine.
5. Reaction with dilute hydrochloric acid:- When bleaching powder is reacted with dilute hydrochloric acid then all the chlorine gas present in it is liberated:

   

6. Reaction with dilute sulphuric acid:- When bleaching powder is reacted with dilute sulphuric acid then all the chlorine gas present in it is liberated:

   

Uses of Bleaching Powder

1. Bleaching powder is used for bleaching cotton, linen, wood pulp and washing clothes. Its bleaching action is due to the release of chlorine gas from it.
2. It is used for making unshrinkable wool.
3. It is used for disinfecting drinking water.
4. It is also used in the manufacture of chloroform, which is used as an anesthetic in hospitals by doctors before surgery.
5. It is used as an oxidizing agent in many chemical industries.

Test your understanding and answer these questions:

1. What is chemical name and formula of bleaching powder?
2. How bleaching powder is manufactured?
3. What are uses of bleaching powder?

The chemical formula of baking soda is NaHCO₃. The chemical name of baking soda is sodium hydrogen carbonate or sodium bicarbonate.

Manufacture of baking soda

The baking soda can be manufactured on commercial scale by Solvay’s process. The manufacture of sodium carbonate by Solvay process includes many steps which are discussed below:

1. Saturation of sodium chloride with ammonia

First of all a cold and concentrated solution of sodium chloride called brine is saturated with ammonia to get a solution called ammoniacal brine.

2. Carbonation

In the second step the ammoniacal brine prepared in first step is dropped from the top of a tower called carbonating tower and carbon dioxide gas is passed into the tower from near its base. The carbonating tower has partitions which are made up of iron plates with hole in the center and covered with perforated plate. The function of these partitions is to slow down the down coming ammoniacal brine solution so that the upcoming carbon dioxide has enough time to react with it completely.

So as the ammoniacal brine comes down from the top of the carbonating tower, it reacts with carbon dioxide to form precipitates of baking soda or sodium hydrogen carbonate:

Properties of Baking Soda

1. Baking soda is a white crystalline powder which is sparingly soluble in water.
2. The aqueous solution of baking soda is mildly alkaline in nature.
3. Action of heat:- On heating, sodium bicarbonate decomposes to form sodium carbonate as given below:

 

Uses of Baking Soda

1. Baking soda is used for preparing baking powder which is used extensively in the preparation of bread, cakes and other confectionary items.

   Actually baking powder is mixture of baking soda and tartaric acid. When baking powder is mixed in dough for preparing cakes or bread and heated then baking soda decomposes into sodium carbonate and carbon dioxide gas. This carbon dioxide gas tries to come out of the cake due to which the cake rises and becomes light and fluffy. Now the presence of sodium carbonate in cake makes it bitter so to remove its bitterness the tartaric acid reacts with it. If incidentally a baker forgets to add baking powder in the dough during preparation of cakes or bread then it will not rise and will become hard and small in size.

2. Baking soda is also used as an antacid in medicines to remove acidity of stomach because it is alkaline in nature so it has the tendency of neutralizing acids present in the stomach.
3. Baking soda is used in fire extinguishers.

Test your understanding and answer these questions:

1. What is chemical name and formula of baking soda.
2. How baking soda is manufactured?
3. Give uses of baking soda.