Carbon Dioxide

 

Molecular formula: CO₂

Molecular weight: 44     

Occurance

               Carbon dioxide is present in air of which it forms 0.03% by volume and comes in there as a result of the burning of fuels, respiration and decay of animal and vegetable matter. It is found in deep wells, caves and mines since it is heavier than air.

Laboratory preparation of Carbon dioxide

Apparatus required

1. Woulfe’s bottle

2. Thistle funnel

3. Delivery tube

4. Gas jar

Chemical required:

1. Calcium carbonate (CaCO₃)

2. Hydrochloric acid (HCl)         

Principle:

               When calcium carbonate is treated with hydrochloric acid, evolution of carbon dioxide takes place. The gas may be collected by upward displacement of air since it is heavier than air.

               CaCO₃ + 2HCl = CaCl₂ + CO₂ + H₂O

Procedure:

               Take small pieces of calcium carbonate and put in a Woulfe’s bottle. Connect a delivery tube and a thistle funnel as shown in figure. The delivery tube leads gas produced into the gas jar. Through the thistle funnel allow dilute hydrochloric acid to pass in the bottle. The bubble of gas passes through the delivery tube.

Test the jar whether it is filled with the help of a burning match stick. It extinguishes when brought near its mouth.

               The principle of preparation of carbon dioxide gas is used to identify whether a stone is calcium carbonate.

Manufacture of Carbon dioxide

               In industrial scale carbon dioxide is prepared from calcium carbonate, in the presence of coal it is burnt as a result calcium oxide (Lime or quick lime) and carbon dioxide is produced.

               Carbon dioxide = ^heat calcium oxide + carbon dioxide

                              CaCO₃ = CaO + CO₂

Carbon dioxide, thus, produced is collected and sent for use in the industries.

               Calcium oxide is also called lime or quick lime. We use slaked lime or hydrated lime for white washing. When calcium oxide is treated with water hydrates lime (calcium hydroxide) is produced.

                              CaO + H₂O = Ca (OH)₂

Properties of Carbon dioxide

               Physical properties:

1. Carbon dioxide is colourless and odourless gas.

2. It is heavier than air (density 22). Because of this property it can be poured from one vessel into another vessel. In the caves, deep wells and mines carbon dioxide content is more due to its density.

3. It dissolves in water. When soda bottle opened the bobbles which comes is carbon dioxide.    

Chemical properties

1. Carbon dioxide is soluble in water which produces carbonic acid.     

   CO₂ + H₂O = H₂CO₃

  This acid turns blue litmus paper into red.

2. Carbon dioxide is non-combustible and non-supporter of combustion. But when burning piece of sodium magnesium or potassium introduced in a jar containing carbon dioxide we can see black spots and white powder which is carbon and oxide of metal respectively.     

          2Mg + CO₂ =   2MgO + C

          4Na + 3CO₂ = 2Na2CO3 + C

3. Lime water (clear solution) is turned milky when carbon dioxide is passed into it. This is due to the formation of insoluble calcium carbonate.

              Ca (OH)₂ + CO₂ = CaCO₃ + H₂O    

This property is used for test of a gas whether it is carbon dioxide.

               If more carbon dioxide is passed in milky solution it turns into clear solution due to the formation of insoluble calcium bicarbonate.

                              CaCO₃ + H₂O + CO₂ = Ca (HCO₃)₂

Use of Carbon dioxide

1. In the preparation of aerated drinks such as soda water, carbon dioxide is used.

2. When carbon dioxide is cooled at about -78 C, it turns into ice (Dry ice). Dry ice is used as refrigeration and preservation of food stuffs.

3. Carbon dioxide is used by plants in photosynthesis which is the only process of trapping solar energy in natural form. Photosynthesis has made life possible since animals depend on plants.

4. Carbon dioxide is used in fire extinguishers. There are two chemicals in extinguishers which in contact produce carbon dioxide. This is heavier than air and make easier to extinguish fire.

Manufacturing Process of Cement

               Cement is produced by heating a mixture of lime stone and special kind of clay (red clay) from mines. To make cement, the powdered mixture containing one third part of clay and two third part of limestone is made slurry in water. The slurry is passed down from the top of a tall kiln via rotating vessel. The kiln is heated from top so that lower zone of kiln has less temperature. The red ball like structure of the mixture of clay, coal and marble when heated at 600°C is known as cement clinker. Cement clinker is a complex mixture containing calcium silicates and calcium aluminates. Cement is produced when it is powdered

               When cement is mixed with water, it stiffens slowly. The mixture prepared from sand, pebbles and water with cement is called concrete. Cement is used to construct road, bridge, dam canal, houses, etc.

               In our country Himal Cement Factory Pvt.Ltd., situated at Chobhar, Kathmandu, has a capacity of  500 M.T., Hetauda Cement Factory and Udaypur Cement Factory are two other big factories in Nepal.

Manufacture Process of Glass

Glass Fiber Nonwovens Wetlaid Process

               Today, glass is extensively used in various purposes. The major composition of glass is silica (SiO₂). Under suitable condition silicon combines with oxygen and silica is produced.

               Silicon + oxygen = silica

               Si + O₂ = SiO₂

The main source of (natural source) silica is sand. Silica melts at about 1600°C. When it is heated at high temperature it turns into glass. Such glass is used to make special kind of glassware and lab equipments. This glassware when heated to red hot and plunged into water, then also they do not break because pure silica expands due to extreme heat. The glass prepared from pure silica is very much expensive.

               If sodium carbonate is mixed with silica it melts at about 800°C. Due to the reaction between silica and sodium carbonate, sodium silicate is produced.

        Silica + sodium carbonate = sodium silicate + carbon dioxide

         SiO₂ + Na₂CO₃ = Na₂SiO₃ (water glass) + CO₂

Pure sodium silicate is called water glass because it dissolves in water.

Ordinary Glass        

In the manufacture of ordinary glass calcium carbonate (CaCO₃) is added in silica in addition to sodium carbonate. Due to chemical reaction in these compounds under suitable conditions it turns into calcium silicate which does not dissolve in water. Generally, glass is manufacture from a mixture of 50% silica, 15% sodium carbonate, 10% calcium carbonate and 25% glass pieces in a tank furnace. The glass prepared by this process is called soft glass or soda glass. From this type of glass ordinary bottle, ordinary test-tube and ordinary equipments are manufactured.

               Small amount of lead monoxide (PbO) is mixed in the raw materials used to prepare soda glass to manufacture the glass for windows and doors.

               In place of silica, if ordinary sand is used to manufacture glass, it will be green or brownish in color due to presence of iron oxide in sand. Ordinary glass bottles are manufactured from such glass because it is less expensive. Small quantity of metallic oxide is mixed in the composition in addition to raw materials needed, to produce colored glass. For example, cobalt oxide is used to manufacture blue colored glass, copper oxide is used to manufacture red color glass and chromium oxide for green.

Borosilicate Glass

A chemical boron oxide is used in place of small part of silica to manufacture such glass. Due to the sudden fluctuation in heat, these glasses are not affected. These are fine looking and attractive. Such glass is also called Pyres glass.

Lead Crystal Glass
               During manufacture of such glass, in raw materials used, compounds of lead potassium are also used in small quantity. These glasses are very fine looking.

Nature of Glass

               Scientists explain glass as a super cooled liquid. The molecules of glass are in a very slow motion. Therefore in old window glasses the lower portion is comparatively thicker than the top.

PESTICIDES

Fig: Spreading Pesticides by plane

               The crop production is reduced by insects and pests. For the control of insects and pests the chemicals (compounds/medicines) are used called insecticides and pesticides. To fulfil the demand of food for overgrowing population damage of crops from the insects and pests had to be controlled. The chemical used to kill the insects is called pesticides.

               Many chemical substances are used as pesticides. After world war II. Cyanide and nicotine were extensively used to control the pests. Now a days, the compounds containing chlorine and phosphorous are used as pesticides. Some compounds are listed below:

Organophoshporous compounds	Organochlorine compounds
Malathion Parathion Methyl parathion Diazinon Fenitrothion Carbofuran	DDT (Dichlorodiphenyl Trichloroethane) BHC (Benzene Hexa Chloride) Dieldrin Aldrin Lindane Chlordane

               Agricultural production has been strangely increased due to the use of insecticides and pesticides. May be, this is one of the reason that the food grains for the overgrowing population has been fulfilled.

               DDT is one of the extensively used pesticides. But due to the excessive use of the organochlorine compounds abnormalities are caused.

Fig: Effect of DDT

               Due to the use of DDT birds lay less number of eggs and the outer shell of eggs are thin. This has affected in fishery also. Human beings when exposed to an environment of DDT for long time may suffer from cancer. DDT has advantages over disadvantages and due to the reason that it is readily available and cheap, it has been used largly and mostly.

Due to the use of Dieldrin and Aldrin many wild lives have been destroyed and may be the same reasons for the stoppage of its use. The resistance in insects and pests increase when same medicine is used repeatedly and the medicine may not affect them.

INDUSTRIAL CHEMISTRY

 Introduction

               Chemistry is the study of chemical substances. Study of chemistry deals with the identification of the chemical compounds or element in combination and how they combine to produce these compounds. Chemists have made studies on this subject and they have been able to produce artificial and /or synthetic materials such as metals, minerals, etc. due to the invention and discovery of new substances life has been made easier and comfort. Plastics, Polymers, medicines and agricultural products have made a great change in living styles.

Chemical Fertilizers

chemical fertilizer

               The population in being increased in the world day by day. Moreover, the life span of man is increased. It has been believed that there were no such populations in the history of earth. The food required for overgrowing population is to be fulfilled by the man himself. The major part of food is obtained from plants. Carbohydrates, vitamins, proteins, fats, minerals, etc., are obtained from plants only. It is believed that plant leaves are strange laboratories where food is manufactured.

               Living things have 4 important elements in them. They are carbon, hydrogen, oxygen and nitrogen. For the existence of life Phosphorus, potassium, calcium, etc., are also needed. The elements such as boron, chlorine, iron, magnesium, manganese, molybdenum, zinc, sulphur are also necessary in traces.

               Plants take these substances from water. When plants die these elements go into the soil after decomposition by bacteria (microorganism). This is true in case of forest plants and preserved areas but in a cultivated land, the nutrients absorbed by them do not return to soil as stated above. Thus the content of necessary elements gradually decreased resulting in the desertion of land. Due to erosion also the top fertile soil is taken away and plants do not get sufficient nutrients for crop production. To make the land fertile, we have to add manure (organic fertilizer) and fertilizer (inorganic chemical fertilizer) in the soil.

               The basic elements Oxygen, Hydrogen and carbon is flourished by the atmospheric air and water but when the content of other elements decrease, that is, to be fulfilled by fertilizers. The fertilizers can be categorized into two groups:

a)      Organic fertilizer (manure)

b)      Inorganic (chemical) fertilizer

Manure

               Manure is used in village as organic fertilizer since time immemorial. This fulfils the required elements (nutrients) for the crops and plants. Unfortunately this manure (gobbar or compost) is not readily available and we use inorganic fertilizers. Chemical fertilizers are produced from nitrogen, phosphorous, potassium and calcium rich compounds.

Nitrogen

               Ammonium nitrate (NH₄NO₃) is extensively used to supply the requirements of nitrogen for plants. Plants can readily absorb nitrate part of ammonium nitrate. Nitrifying bacteria in soil helps in decomposition of nitrate from ammonium nitrate.  Such nitrate is soluble in water and thus, plants can absorbs easily. Plants become yellow and wilting due to insufficient amount of nitrogen in soil.

               Ammonium sulphate (NH₄)₂SO₄ and Urea (CO (NH₂)₂) are other nitrogen rich fertilizers.

Phosphorous 

               Ammonium phosphate (NH₄)₃PO₄ fulfils the required phosphorous in soil. Bone meal and calcium superphosphate are chemical fertilizers rich in phosphorous. A mixture of calcium hydrogen phosphate and calcium sulphate is called super phosphate. For the growth of root and better quality crops phosphorous is essential.

POTASSIUM

 POTASSIUM sodium

               Another important element necessary for the growth of plant is potassium. A fertilizer containing potassium is called potash. For the manufacture of food in plants this elements is necessary. Lack of potassium results slow maturation of plant and flowers. This increases the disease resistance. The chemical fertilizers such as potassium sulphate and potassium chloride are used to fulfils the required amount of potassium. Since time immemorial wood ash has been used in soil to supplement potash in soil.

Calcium

Dietary calcium

               Calcium oxide (CaO) is used for the requirement of calcium in soil. This reduces the acidity of soil and makes land more fertile.

Danger from Chemical Fertilizers

               The quality of soil is to be tested to find out the quantity of elements lacking in soil. At the mean time, its acidity and basicity is also to be tested before planting the crops because the plants which grow in acidic soil cannot grow well in basic soil and vice-versa. Moreover, in high acidic or basic soil no plants can grow. With reference to the soil test, only the required fertilizer is to be used to enhance the fertility of soil. But excess use of same fertilizer may lead towards desertion. For example, if nitrate fertilizers are not totally absorbed by plants they will be swept away by water to near water source. Due to excessive nitrates in water algal growth will increase. But as the algae die dissolved oxygen is extremely used by the decomposers. As a result aquatic animals die due to the lack of oxygen. Drinking nitrate rich water results dwarfism in children, which are the adverse affected of fertilizers.