WBBSE Notes For Class 8 School Science Chapter 4 Occurrence Of Carbon And Its Compounds In Nature

Chapter 4 Occurrence of Carbon and Its Compounds in Nature

 

Existence of Carbon in Nature

Carbon in Life

The Latin word “carbo”, meaning coal, has been transformed into the English word carbon. Carbon is regarded as the building block of life.

Plant and animal bodies are made of carbon and its various compounds. For example, carbon is a major constituent of all biological molecules such as benzene, xylenes, etc. all as DNA (Deoxyribose Nucleic Acidjand RNA (Ribo Nucleic Acid), proteins, and carbohydrates, etc.

Small molecules like ATP, lipids, hormones, and enzymes – all are made up of carbon. Carbon comprises nearly 50% of the total mass of the body.

Source of Carbon

In a free state, carbon exists in crystalline states (such as diamond and graphite) as well as amorphous states (such as coal, charcoal, gas carbon, etc.).

In combined state carbon exists in various biomolecules such as carbohydrates, proteins, DNA, RNA, enzymes, etc. Oils and fats also contain carbon as one of their constituents.

In combination with hydrogen, it exists as hydrocarbons in the form of petroleum products, marsh gas, etc. Carbon is abundant in the earth’s crust.

As minerals, it exists in limestone (CaC03), dolomite (MgC03, CaC03), magnesite (MgC03), calamine (ZnC03), marble (CaC03), etc.

In the air, carbon exists as carbon dioxide and methane.

The shells of small marine animals such as mollusks are made of calcium carbonate. Even the materials used for making our garments (such as silk, wool, jute, etc.) are polymers of carbon.

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Uses Of Carbon

Several modern furniture, electronic equipment, sports accessories, etc. are being manufactured using polymers of carbon. Lifesaving drugs, solvents like alcohol, ketones, ether, and chloroform compounds of carbon.

Carbon compounds are abundant in nature and a wide variety of man-made materials which have carbon as one of the constituents are being synthesized every day.

Carbon Cycle

The carbon cycle is the circulation and transformation of carbon back and forth between living things and the environment. The total amount of carbon present in the earth and the earth’s atmosphere is fixed. But the amount of carbon present in different compounds is always changing.

The carbon cycle is the bio-geo-chemical cycle by which carbon is exchanged or cycled among the earth’s oceans, atmosphere, ecosystem, and geosphere.

Occurrence Of Carbon And Its Compounds In Nature

The atmosphere acts as a reservoir of carbon in the form of carbon dioxide. Carbon is released to the atmosphere from what we call carbon sources and is stored in plants, animals, rocks and minerals, and water, which we call carbon sinks.
Now, let us discuss various processes of the carbon cycle.

Removal of carbon as CO₂ from

1. By fixation of atmospheric carbon dioxide: Carbon exists in the atmosphere mainly as CO₂ and methane (CH4). A large amount of CO₂ is utilized by green plants to produce glucose, using water and sunlight through a process called Photosynthesis. Thus carbon becomes part of their body.

Glucose is then converted into different complex organic molecules within the body. So atmospheric CO₂ is “fixed” by the green plants into different organic compounds in a living cell.

This carbon fixation step is also known as carbon assimilation. Some anaerobic bacteria can convert carbon monoxide into organic compounds.

 

 

2. Through the formation of CaC03 by marine animals: Oceans contain very large amounts of carbon. Some amount of carbon dioxide present in the atmosphere dissolves in water and is converted into carbonates and bicarbonates. For example, dissolved CO₂ can be converted into carbonate rocks such as limestone.

Many marine animals also absorb CO₂, which is dissolved in water. Their shells contain carbon in the form of calcium carbonate (CaC03).

A part of the dissolved CO₂ is converted into organic carbon (i.e. carbon present in organic substances) by microorganisms through photosynthesis. In such a form, carbon can be exchanged throughout the food chain.

3. By conversion of CO₂ into carbonate minerals: Carbon dioxide in the atmosphere can be converted into carbonate rocks. Marble, limestone, dolomite, etc.

Are all carbonate minerals. Limestone caves have columns of stalactite and stalagmites which are made up of calcium carbonate. (Some limestone caves have been found in India also. Bora caves in Araku valley is one such example.)

By dissolving of atmospheric CO₂ by rainwater: The atmospheric CO₂ is dissolved in rainwater and is converted into carbonic acid. This is dissociated into bicarbonate ion (HC03)

1. Generation of CO₂ through respiration and oxidation of food: As we have just pointed] [out carbon in the earth’s atmosphere exists in two main forms carbon dioxide and methane.

Green plants absorb CO₂ from the atmosphere and are converted to glucose. When this glucose is oxidized within the plant body during respiration, CO₂]), which is ultimately converted into carbonate compounds such as calcium carbonates formed and released into the atmosphere.

Animals and humans inhale air (containing oxygen) and exhale CO₂ produced by the metabolism of food which is derived directly or indirectly from green plants.

2. By degradation of dead organisms: Living organisms are composed of organic compounds. After the organism dies, its body is broken down by bacterial and fungal action.

There are several different types of bacteria and fungi that can degrade complex organic compounds containing carbon into simple compounds.

Due to such processes, some carbon compounds remain stored in soil and water, and some return back to the atmosphere in the form of CO₂.

Methanogenic bacteria which are available in wetlands and rain forests can decompose dead plants into methane (CH4), which is released into the atmosphere.

Microbes present in the rumen of cattle and intestines of termites can produce methane from cellulose.

3. By human activities: The continuous and steady increase in the concentration of CO₂ in the atmosphere is mostly caused by human activities (i.e. anthropogenic).

These include the burning of carbonaceous fossil fuels (coal, oil, natural gas), clearing and burning of forests (mainly for agriculture and cattle(grazing), cement manufacture, etc.

4. By natural phenomena: Natural phenomena like volcanic eruptions and forest fires also contribute large amounts of carbon dioxide and carbon monoxide to the atmosphere.

5. Due to saturation of dissolved CO₂ in ocean water: Ocean water has huge quantities of CO₂ dissolved in it which is vital for marine plants.

Scientists have estimated that almost 50% of CO₂ having anthropogenic origin is absorbed in the oceans. But the steep increase in the production of CO₂ by human activities severely imbalances the capacity of the oceans to store additional CO₂ and as a result, a large amount of CO₂ remains unabsorbed.

6. By marine organisms: Carbon is stored in the shells of marine organisms as calcium carbonate (CaC03). When these shells are heated at high temperatures, CO₂ is released into the atmosphere.

Allotropy

Substances such as diamond, graphite, charcoal, coke, coal, etc. may physically appear different, but – they are all made of carbon.

If a fixed mass of all these substances is heated strongly in presence of pure oxygen, the same mass of carbon dioxide is formed in all the cases.

The phenomenon in which some elements like carbon, sulfur, phosphorus, etc. exist in more than one form, generally having the same chemical properties but some differences in physical properties in the same physical state is known as allotropy.

The different forms of an element having the same chemical properties but with different physical properties are called allotropes.

Causes of allotropy:

1. The difference in the mode of arrangement of atoms in molecules
2. Number of atoms present
3. Different methods of formation
4. Different amounts of internal energy are associated with the formation of each allotrope
5. Allotropes of Carbon
6. The element carbon has a number of allotropes and they may be classified as follows,

 

 

Generally, the allotropes of carbon can be seen in two forms.

1. Crystalline and
2. Amorphous.

1. Crystalline forms of carbon

1. Diamond

It is one of the hardest substances known to us. It is a transparent, hard solid with a high refractive index. This hardness of a diamond can be related to its internal structure.

Here, every carbon atom is surrounded by four other carbon atoms This arrangement is known as a tetrahedral arrangement.

 

 

 

This is responsible for the rigidity, high density, and very high melting point of diamonds. Diamond is a very good conductor of heat. It has the highest thermal conductivity among the elements.

Diamond is a poor conductor of electricity. Chemically also it is quite inert. Its extreme hardness of it makes it suitable for making the tip of a boring drill that bores through rocks.

 

 

2. Graphite

The name is derived from the Greek word “Grapho” which means “I write”. It can put marks on paper. It is available in the free state of Sri Lanka, Mexico, and in the state of Rajasthan in India.

Graphite has a layered structure where two-dimensional sheets made of carbon are arranged parallel one over the other. The distance between two successive layers is relatively large and hence the force of attraction between the successive layers is weak. So when force is applied, one layer slides over the other.

 

 

In each two-dimensional sheet, carbon atoms are arranged in a hexagonal planar fashion. Graphite is grayish in color. It is soft.

It is a good conductor of heat and electricity. That is why it is used as electrodes. A suspension of graphite in oil is used as a lubricant. Chemically, graphite is more reactive than diamond but less dense than diamond.

 

 

Comparison between diamond and graphite

Similarities between diamond and graphite:

 

Diamond	Graphite
1. Has crystalline structure.	1. Has crystalline structure.
2. Chemically very less active.	2. Chemically not very active.
3. Burns at high temperatures (800°C-850°C) in	3. Burns at high temperatures (700°C) in oxygen
oxygen to produce COr	to produce CO2.
4. Cannot absorb any gas.	4. Cannot absorb any gas.
5. Good conductor of heat	5. Good conductor of heat.

 

Dissimilarities between diamond and graphite:

 

Diamond	Graphite
1. Hardest natural element.	1. Soft and slippery element.
2. Colourless and transparent.	2. Blackish grey and opaque.
3. Non-conductor of electricity.	3. Good conductor of electricity.
4. Cannot put marks on the paper.	4. Can put a mark on the paper.

 

3. Fullerene

Fullerene – a new allotrope of carbon was first characterized in 1985 in the laboratory by Smalley and Kroto. This is a hollow, closed cage (polyhedral) cluster of 60 or 70 carbon atoms.

Its structure is based on polyhedra formed by fusing pentagons and hexagons-which is very much similar to geodesic domes used in architecture.

Fullerene is named after American architect R. Buckminster fullerene – the inventor of the geodesic dome. It has been subjected to extensive research since its discovery and is a promising candidate for use in electronics and medicines. It can be used to produce novel enclosure compounds by trapping metal ions within the C60cage.

 

 

Amorphous allotropes of carbon

Various amorphous forms of carbon such as soot, carbon black, coke, coal, charcoal, etc. are all microcrystalline forms of graphite.

Coke can be used as fuel during metal extraction and as a reducing agent in redox reactions. Coal is primarily used as fuel.

Lamp black is used as a pigment and used for making printing ink for use in the printing press. Gas carbon is used to make electrodes for batteries, arc lamps, or electrolytic cells.

 

 

Charcoal has a remarkable property of adsorption. (Note that it is “adsorption” and not “absorption”). It can adsorb impurities from water and hence can purify water.

Specially prepared charcoal, known as activated charcoal, can adsorb large amounts of gas on its surface, so it is used to prepare gas masks.

Adsorption on charcoal: The adsorption property of charcoal can be easily shown by the following experiment. Let us take some amount of finely crushed charcoal powder.

Now dissolve some ink or some color in a small volume of water taken in a bottle with a lid. Now pour the charcoal powder in it and close the lid.

Then shake the bottle well for some time and then be allowed it to settle. Now the solution containing the charcoal dust is filtered.

It will be found that the intensity of the color of the solution after filtration has diminished considerably, indicating that a significant fraction of the molecules responsible for coloration has been “adsorbed” on the charcoal.

So, by filtration, when the solid charcoal powder is separated, the intensity of the color in the filtrate decreased.
Very recently another form of carbon- called graphene (consisting of planar sheets with atoms arranged in a honeycomb shape) has been discovered and looks promising for use in the field of nanotechnology.

 

All the allotropes of carbon contain the same element carbon

If samples of different allotropes of carbon are separately burnt in oxygen, carbon dioxide gas is produced in each case.

The gas can be tested by passing it into clear lime water that turns milky. This proves that each of the allotropes contains the same element carbon.

Again, burning equal weights of different allotropes of carbon in excess oxygen separately, the gas produced in each case is absorbed in a previously weighed tube containing caustic potash.

It will be observed that the increase in weight of each tube is the same, ie. an equal quantity of each allotrope produces the same amount of carbon dioxide gas.

 

Heating Value/Calorific Value of Fuel

Fuel includes all combustible substances that undergo oxidation or combine with oxygen from the atmosphere with the evolution of large amounts of heat capable of being economically applied to domestic or industrial purposes.

Examples of fuels are wood, coal, LPG, kerosene, diesel, petrol, etc. All these fuels contain carbon as the main constituent, so they are called carbonaceous fuels.

Fuels like hydrogen are not carbonaceous. In our everyday life, we use various types of fuels for different purposes.
The amount of heat released during the burning of different fuels is different.

 

 

Depending on the amount of heat released by a fixed mass of a particular fuel, it is used for specific purposes.

The amount of heat generated on the complete combustion of 1 kilogram of fuel with oxygen is called the heating value or calorific value of that particular fuel. It is generally expressed in units of kilocalorie per kg. or kilo Joule per kg.

Among all the fuels, hydrogen (150 kJ/g) has the highest heating value followed by LPG (liquefied petroleum gas). Wood has the lowest heating value among the above-mentioned fuels.

Classification of Fuels

Classification of fuels depends on several As per Physical state at normal pressure & temperature Primary Secondary Primary fuels are naturally occurring fuels in nature.

Examples: Wood, coal, petroleum, natural gas, etc. Secondary fuels are prepared or derived from primary fuels. Charcoal, semicoke, coke, kerosene, coke oven gas, etc are secondary fuels.

 

 

Fuels can be either vegetable (organic) or mineral (inorganic). Coal is an example of organic fuel while elemental sulfur, iron pyrites, etc are mineral or inorganic fuels.

Fuels can be classified into three classes on the basis of their physical state at normal temperature and pressure. They are solid, liquid, and gas. In the following table, different fuels are classified under these three categories and their uses are mentioned.

 

Physical State	Name of the Fuel	Calorific value	Uses
Solid	Wood	17 KJ/g	Cooking, for generating heat in colder countries
	Coal	(25-30)KJ/g	Cooking, generation of electricity, steam engines, preparation of bricks, etc.
Liquid	Kerosene	48KJ/g	Domestic purposes like cooking
	Petrol	50KJ/g	Automobile fuel
	Diesel	45KJ/g	Automobile fuel, diesel engines, industries
Gas	LPG (Liquefied Petroleum Gas)	50KJ/g	Domestic purposes such as cooking
	CNG (Compressed Natural Gas)	33-50 KJ/g	Automobile fuel

 

Conservation of Fuels

The advancement of modern civilization is dependent on the use of fuel. The fuels we mostly use nowadays are fossil – such as petroleum oil, coal, natural gas, etc.

Millions of years ago, prehistoric, plants and animals were buried under the earth probably due to severe earthquakes or another natural disaster of gigantic magnitude.

Their remains were decomposed under the high pressure of the earth in absence of air and were transformed into fossil fuels.
So, we can understand that the stock of fossil fuels available on the earth is limited.

But the irony is that the demand and use of fossil fuels are increasing every day. In the last century alone, we have burnt 90% of the total fossil fuel we have burnt during the total history of mankind.

If the demand for fossil fuels increases at such a rate, then all fossil fuels will be consumed probably by the end of the 21st century.

So we must have to think of ways to prolong the availability of fossil fuels and maintain a continuous and undisturbed supply Of energy for our various needs.

The strategies for this can be classified into two categories –

Judicious and optimized use of available fossil fuels Use of alternative sources of energy such as solar energy, wind energy, atomic energy, etc.

Judicious and optimized use of available fossil fuels: Since the stock of fossil fuels is limited and so far most of them have been consumed by human beings, hence, the rest of the fossil fuels still left have to be used rationally.

For example, coal is of two types – high-grade coal (having a higher calorific value) and low-grade co; (-having a lower calorific value).

The reserve of high-grade coal is smaller compared to the reserve of low-grade coal. High-grade coals should be used specifically for the generation of electricity, while low-grade coals should be used for domestic purposes such as cooking,

In coal mines areas, for example in Raniganj, Asansol, Jharia, etc. underground fires are slowly but steadily destroying our valuable coal reserves. This must be extinguished and care must be taken during mining so that no new fires break out.

Natural gas is available in various regions such as river basins etc. They have high calorific value and can be used for different purposes such as fuel for automobiles, generating electricity, etc.

But in many cases, natural gases are just burnt, thus a vital source of energy is simply wasted. The potential of natural gas as a natural source of energy has to be fully utilized.

The development of more efficient heat engines (which consumes less fuel and produces more work) can reduce the consumption of fossil fuel.

The development of energy-efficient electrical instruments and gadgets can ultimately reduce the consumption of electricity which in turn saves precious fossil fuel.

Use of public vehicles and carpooling can be encouraged instead of private vehicles.

The use of vehicles that do not require fossil fuel can be encouraged. For example, the use of bicycles on roads or non-mechanized boats in water can significantly reduce the consumption of fossil fuel.

In several countries, separate tracks for bicycles have been prepared to encourage the use of bicycles by the general public.

Use of alternative sources of energy: Fossil fuels are the conventional source of energy. But they can be substituted by alternative, non-conventional sorts of energy.

They include solar energy, wind energy, geothermal energy, tidal energy, bio-fuels, atomic energy, etc.

1. Solar energy

Solar energy is the most readily available source of energy. Solar energy has been used since prehistoric times for different purposes. But after 1970, when prices of petroleum soared, extensive research programs were initiated worldwide to exploit solar energy.

It can be used to generate electricity using solar panels on rooftops. Solar panels contain photovoltaic cells, which absorb the light energy of the sun and convert it to D.C. electricity directly.

This electricity can either be used immediately or can be stored in a battery for future use. This can be used for a number of applications such as domestic lighting, street lighting, rural electrification, water pumping, desalination of salty water, powering of remote telecommunication devices, etc.

India is one of the few countries with long daytime and plenty of sunshine. So in a country like India, the potential of solar energy can be best exploited.

2. Wind Energy

Wind energy is also an effective alternative to fossil fuels. This form of energy is free, plentiful, and renewable. Winds are caused by uneven heating of the atmosphere by the sun and the rotation of the earth.

This wind flow (or energy due to the motion of wind) can be converted to electricity by using wind turbines. A wind turbine is basically the opposite of a fan.

Wind turbines use the wind to make electricity. It has long blades. The wind turns the blades, which spin a shaft that is connected to a generator and electricity is produced.

During this operation, no greenhouse gas is emitted. So it is an “environmentally clean” alternative to fossil fuel.

 

3. Geothermal energy

Geothermal energy is the earth’s heat. Below the crust of the earth, the top layer of the mantle is a hot liquid rock called magma.

The crust of the earth floats on this liquid magma mantle. (When magma breaks through the surface of the earth in a volcano, it is called lava.)

Generally, for every 100 meters we go down, the temperature of the earth increases by about 3 degrees Celsius. So, if we go down to about 3000 meters below the ground, the temperature of the rocks there would be hot enough to boil water.

Deep under the surface, water sometimes makes its way close to hot rocks and turns into boiling hot water or into steam. When this hot water or steam comes upwards through a crack, we call it a hot spring.

There are many hot springs in India, but the potential of this energy source has not been exploited so far. The steam coming out from these hot springs can be directly used to rotate the turbine and thus produce electricity.

 

4. Biomass, Biogas, and Bio-fuel

1. Biomass is the term commonly used for the biological material derived from living or recently living organisms such as wood, waste materials, gases, and alcohol fuels.

In other words, it is dead material that was once living. It is a renewable energy resource derived from the carbonaceous waste of various human and natural activities.

It is derived from numerous sources, including by-products from the timber industry, agricultural crops, raw materials from the forest, major parts of household waste, and wood.

The composition of biomass is carbon, hydrogen, and oxygen. In addition, biomass energy is gaining significance as a source of clean heat for domestic heating and community heating applications.

 

2. Biogas:

Biomass can be converted to other usable forms of energy like biogas. This is generally prepared by the digestion of organic waste in absence of air.

Methane is produced from organic waste in this process. Organic waste includes municipal waste and drained water, agricultural waste like rotten vegetables, fruit pulp, feces of domestic animals, etc., human waste, left-over food products, etc.

In rural India, biogas technology is actively utilized. It is particularly useful for village households that have their own cattle.

The cattle dung is converted to biogas by a simple process and this biogas is used as fuel for cooking. So biogas plants are becoming quite popular in rural India.

 

3. Bio-fuel:

Biofuel is a fuel that is derived from biological materials, such as plants and animals. In more simple way we can say that bio-fuels are liquid and gaseous fuels produced from biomass.

So any hydrocarbon fuel that is produced from organic matter (living or once-living material) in a short period
of time (days, weeks, or even months) can be considered a biofuel.

Typical feed-stocks used for producing biofuel include sugarcane and sugar beet, starch-bearing grains like corn and wheat, oil crops like canola, soybean, and palm oil, and in some cases animal fats and used cooking oils.

Ethanol, bio-diesel, and methanol are the three most important examples of biofuels. Bioethanol is an alcohol made by fermentation, mostly from carbohydrates produced in sugar or starch-containing crops such as corn, sugarcane, etc.

Cellulosic biomass, derived from non-food sources, such as trees and grasses, is also being developed as a feedstock for ethanol production.

Ethanol can be used as a fuel for vehicles in its pure form, but it is usually used as a gasoline additive.
In India, bio-fuels are produced from oil obtained from the seeds of Jatropha plants.

Since Jatropha can be cultivated in less fertile and dry lands, so its cultivation is economically beneficial from the perspective of our country.

 

5. Tidal energy

Tidal energy is a form of hydropower that converts the energy of tides into more usable forms of energy, such as electricity. Tidal energy is produced by the surge of ocean waters during the rise and fall of tides. High tide and ebb always occur twice a day.

Unlike wind, tides are predictable and stable. Usually, turbines are placed in tidal streams (a fast-flowing body of water created by tides).

The kinetic energy of the tidal stream is utilized to rotate turbines which in turn produce electricity. Tidal energy is more powerful and effective than wind energy.

Since, our country has very long coastlines, so this form of renewable energy can be effectively utilized as an alternative form of energy.

 

6. Atomic energy

Neutrons and protons are bound within the nucleus of an atom by nuclear energy, if the nucleus is disintegrated, a huge amount of energy is released.

This energy can be utilized to generate electricity. Atomic energy can be generated by a process known as nuclear fission.

[Fission reaction was discovered by Otto Hahn and F. Strassmann in 1939. In this process nuclei of very heavy elements such as uranium, plutonium, or thorium are excited mainly by hitting them with a high-energy neutron.

As a result, the nucleus undergoes disintegration, producing two fragments along with a huge amount of energy. Otto Hahn was awarded Nobel Prize in 1944].

There are numerous electric power generating stations throughout the world, including India, which are based on nuclear fission technology.

In India, Dr. Homi J. Bhabha first envisioned a program for generating electricity utilizing atomic energy. This started with the setting up of Tarapur Atomic Power Station in 1969 in Maharashtra.

Later, several atomic power stations became operational, such as Rajasthan Atomic Power Station in Kota, Rajasthan (1973), at Kudankulam in Tamilnadu, Kalpakkam in Kerala (1985) and Kakrapar in Gujarat (1991), etc.

It is estimated that by the end of the year 2032, approximately 63,000 megawatts of electricity will be generated using atomic energy.

In the developed world, such as France nearly 70% of its electricity is generated by utilizing atomic energy. Nearly 40% of the total electricity generated is produced from atomic energy in countries like USA, UK, Germany and Japan.

The vast deposits of thorium available in India can be exploited to generate atomic energy.

But keeping in mind the incidents that happened in Chornobyl in Russia and Fukushima in Japan, proper care and round-the-clock maintenance is required in all atomic energy power plants.

Nuclear waste management is also a big issue that must be resolved since the fragments derived from the disintegration of the heavy nucleus are radioactive and so hazardous. Generally, the radioactive nuclear wastes are buried underground in sealed, thick-walled steel drums.

 

7. Solid waste

In many metropolitan cities, solid wastes are being utilized to produce electricity. Solid wastes are burnt and the heat generated is used to produce steam, which ultimately rotates a turbine to produce electricity.

But, solid wastes available in metropolitan cities contain a large variety of materials, and some of them can cause serious environmental pollution during their burning.

 

Hazardous effects on the environment due to the combustion of fossil fuel

1. Fossil fuel serves as the most important source of energy in today’s world. But the use of fossil fuels also is the cause of environmental pollution.

During incomplete combustion of carbonaceous fuels like wood, coal, and petroleum, unburnt carbon particles are produced which float in the air.

1. When inhaled, these suspended particles may deposit within the nose, throat, and respiratory tracts. This may cause respiratory problems.

2. The incomplete combustion of carbonaceous fossil fuel produces carbon monoxide which is very poisonous.

3. Complete combustion of carbonaceous fuel produces carbon dioxide (CO₂). The increasing concentration of CO₂ in the atmosphere is mainly responsible for global warming.

4. During the combustion of coal and diesel, sulfur dioxide (S02) is produced. During combustion at elevated temperatures, the nitrogen in the air is converted to oxides of nitrogen (commonly called NOx).

The oxides of carbon, sulfur, and nitrogen are acidic in nature and react with rainwater to produce acids such as sulphuric acid (H2S04), nitrous acid (HN02), nitric acid (HN03), and carbonic acid (H2C03).

These acids, dissolved in rainwater cause acid rain. Acid rain is harmful to crops, soil, and buildings. It can also affect aquatic ecology.

5. Excessive use of fossil fuels causes the release of greenhouse gases (eg. CO₂, N0x) that results in global warming.
Compared to these fossil fuels like coal, coke, petroleum products, etc.,

CNG and LPG are cleaner fuels. Complete combustion of LPG and CNG is relatively easy and their efficient combustion produces very low carbon particles (or soot).

 

Greenhouse Effect

Principle of action of greenhouse: A greenhouse is a house made of glass. It is used for raising plants of vegetables, fruits, and flowers in cold temperate regions where the growing of plants in the open fields becomes impossible due to severe cold.

During the daytime, sunlight enters the room through its glass walls and roof and warms the plants and air present inside the room.

Sunlight reaches earth through invisible radiation, called infrared radiation (IR radiation), which is primarily responsible for the sensation of heat.

But the heat generated by sunlight cannot be stored for an indefinite period and hence after some time the absorbed heat is radiated.

The radiated heat or emitted heat is less energetic than the original heat of the sunray which initially entered the glasshouse.

This emitted radiation cannot pass through the glass walls and roof. So some amount of heat is trapped inside the glass house and cannot escape. So during the daytime, the inside of the house gets warmer and stays quite warm during the night too.

Greenhouse gases and greenhouse effect: Gases present in the earth’s atmosphere such as carbon dioxide, water vapor, methane, nitrous oxide, ozone and some other man-made chemicals (such as chlorofluorocarbons) do exactly what the glass roof and walls do in a greenhouse.

They are known as greenhouse gases. The molecules of these gases cannot absorb solar radiation directly coming from the sun. Hence, during the daytime, the earth’s surface warms up.

At night it cools down by radiating the heat back to space. But a part of this low-energy infrared radiation, radiated by the earth, is absorbed by molecules of greenhouse gases.

Thus heat is trapped by the greenhouse gases in the atmosphere and is redirected again back to earth. This mechanism keeps the earth warm.

This is a natural phenomenon known as the greenhouse effect- So the earth’s surface remains warm and cozy which is essential to sustain life on earth.

 

 

But if the greenhouse effect is high, the earth’s surface gets warmer than what is required. This is known as the enhanced greenhouse effect or more commonly just Greenhouse Effect.

1. The presence of greenhouse gases in much greater concentration than the normal level is responsible for this enhanced greenhouse effect causing global warming.
2. The steps which are occurring during the enhanced greenhouse effect may be approximately summarized below:
3. Solar radiation reaches the earth
4. Sun’s energy is absorbed by the land and the oceans, and the earth’s surface becomes warm
5. During the night, heat is radiated by the earth back to space.
6. Some of the heat is trapped by the greenhouse gases present in the atmosphere, keeping the earth warm enough to sustain life.
7. Human activities such as burning fossil fuels are increasing the concentration of greenhouse gases in the atmosphere rapidly.
8. Trapping of the extra amount of heat causes the earth’s temperature to rise above normal and this leads to the phenomenon known as the enhanced greenhouse effect or more commonly greenhouse effect.

 

Sources Of Green House Gases:

Human activities, particularly the burning of fossil fuels (such as coal, oil, natural gas, etc.) and heating limestone in cement factories are increasing the concentration of greenhouse gases such as CO₂ rapidly.

Some bacteria known as denitrifying bacteria found in soil reduce the nitrate in several steps and during the process produce greenhouse gases such as nitrous oxide.

Methane (CH4) is another greenhouse gas that has about 20 times more greenhouse effect than CO₂. Methanogenic bacteria present in wetlands and rainforests produce methane.

Bacteria present in the rumen of cattle and in the intestine of termites also produce methane.

4. Use of chlorofluorocarbons (CFCs) in refrigeration and air conditioning systems and the use of CFCs and Halons in fire extinguishing systems contribute to rising in greenhouse gas concentrations.

The major concern is that the concentration of many greenhouse gases is increasing at an alarming level. The volume of CO₂ in the atmosphere has increased by over 35% in the last three hundred years.

Generally, the earth has its own mechanism for maintaining the level of CO₂ in the atmosphere. But if the level of such gases increases rapidly, this mechanism is bound to fail and this will increase the temperature of the earth. This will lead to Global Warming.

Result of global warming: As a direct consequence, the polar ice caps (in which more than 90% of the earth’s total drinking water is stored) will melt.

So the water level in the oceans will rise and several coastal cities (having a habitat of millions of people) will submerge. The ecosystem will be adversely affected.

Increasing temperature will enhance the growth of mosquitoes which in turn, will spread mosquito-borne diseases. Biodiversity will be hampered and several parts of the world may face drought-like conditions for a prolonged time. In short, the effect of the greenhouse effect (or enhanced greenhouse effect) will bring devastation.

Carbon-Containing Polymers and Their Uses

The modern age is often termed as plastic age. If we look around we can see a wide range of materials starting from rubbers, plastics, paints and surface coatings, resins, adhesives, etc.

Some of them are naturally obtained, and some of them are artificial (i.e. manufactured in a laboratory or industry). They all belong to a particular class of compounds known as polymers.

“Poly” means many and “meros” means parts. Polymers are high molecular weight compounds that are made up of a large number of (few hundred to few thousand) simple, repeating units called monomers.

In today’s world, we use a variety of carbon-containing polymers for a variety of purposes. Polythene, thermocol, nylon, etc. are all carbon-containing polymers.

The large size and their shapes are the two most important properties which are utilized for different purposes. Some of the polymers are flexible and some are hard.

Some are heat resistant and very good insulators of electricity. Some polymers have a high melting point and some are chemically quite inert.

Depending upon the need, one can choose a polymer that suits best a specific purpose. Plastics are sometimes used by common people to indicate all types of polymers.

But actually, polymer and plastics are not at all synonymous. Plastics are a special type of polymer.

 

 

Let us discuss briefly some common carbon-containing polymers, such as polyethylene, Teflon, PVC, nylon, and terylene.

1. Polythene (or Polyethylene)

Polythenes generally show excellent chemical resistance, meaning that it is not attacked by strong acids or strong bases.

It is also resistant to mild oxidizing and reducing agents. Polyethylene burns slowly with a blue flame. Crystalline samples are not soluble at room temperature but are usually soluble at higher temperatures in toluene, xylene, and chlorinated solvents. It is an insulator of electricity.

Uses of polythene: Polythene is widely used for food packaging, milk carton lining, and making shopping bags. It is used to make squeezable bottles, drums, and containers for different purposes.

High-density polyethylene is used to make dustbins, crates, buckets and bowls, food boxes, etc. It is also used to coat paper, which is then rendered a waterproof surface.

Pipes and hoses, flexible water pipes, etc. are made of polyethylene. Since it is an insulator of electricity it is used for coating electrical cables.

2. Teflon

Teflon is a high-molecular-weight compound consisting wholly of carbon and fluorine. It has a high melting point, very good insulator of electricity, and is chemically quite inert (even towards strong acids like aqua regia).

This is because of the very strong bonds between carbon and fluorine. It is a hydrophobic material (i.e. water cannot wet it). It experiences a very low frictional force against a solid surface.

Uses of Teflon: Most of us know Teflon for its non-stick properties in cookware applications. Teflon coatings are applied on a range of cookware as it is hydrophobic and possesses fairly high heat resistance.

Besides Teflon is widely used for wiring in aerospace and computer applications. It is used for making cables and connector assemblies.

In industrial applications, owing to its low friction, it is used for applications where the sliding action of parts is needed.

PVC (polyvinyl chloride)

PVC is the abbreviation of polyvinyl chloride. It consists of carbon and chlorine. PVC was accidentally synthesized in 1872 by German chemist Eugen Baumann.

The polymer appeared as a white solid inside a flask of vinyl chloride that had been left exposed to sunlight. Industrially, PVC is prepared from petroleum.

PVC is a relatively low-cost material. It has high hardness and mechanical properties. It is available both as transparent and opaque substances.

It is chemically and biologically quite inert and it is inert towards different solvents such as water, oil, petrol, and other chemicals. So, it is biocompatible.

The most important characteristic of PVC is its high fire resistance. As a result, it has found application for a wide variety of substances.

Uses of PVC: Since PVC is highly fire resistant, it is widely used in exterior construction materials such as window profiles, siding boards, or interior housing materials, such as wall-covering and flooring.

Fire-resistance property of PVC is used widely in a variety of applications such as electric cables for residential buildings, vehicles, household electrical appliances, cable coverings, insulating tapes, switch boxes, wire coverings, and protecting tubes for power and telecommunications cables.

It is used for sewerage pipes and other pipe applications where cost or vulnerability to corrosion limits the use of metal.

PVC is widely used in clothing, to either create a leather-like material or at times simply for the effect of PVC. PVC is used for preparing flexible containers and tubing – containers used for blood and blood components, for urine collection and tubing used for blood taking and blood giving sets, catheters, heart-lung bypass sets, hemodialysis sets, etc.

4. Nylon

Nylon is a polymer and is frequently referred to as polyamide. Nylon is a silky material. It is transparent. Strong, water-resistant fibers can be made from this material.

It can sustain high temperatures. Nylon was first used commercially in a nylon-bristled toothbrush (1938), and within the next couple of years, it was commercially introduced as a fabric.

In 1939, World War 2 started. During World War 2, when Asian silk and different products made of silk became scarce, extensive research was carried out to develop Nylon as a synthetic replacement for silk.

Uses of nylon: Soon it replaced silk in military applications such as parachutes and flak vests, and was used in many types of vehicle tires.

It was also used to make tents, ropes, and other military supplies. Nylon is being used for those purposes still today. Nylon fibers are used by the carpet manufacturing industry.

They are also used for making fishing lines and musical strings. Nylon resins are used for making food packaging films. Nylon has been used for meat and sausage wrappings.

5. Terylene

Polyester is a polymer where the individual units are held together by “ester linkage”. When it is used as a fiber to make clothes, it is then sometimes known as “terylene”.

When it is used to make bottles, it is usually called PET (polyethylene terephthalate). This material is soft and flexible, resistant to stains, and does not absorb water. It can produce long and strong fibers, which are resistant to folding and has a long life.

Uses of terylene: So it is widely used as fibers to make clothes. Terylene can be used together with cotton fibers to make a material known as tricot (terylene + cotton).

As a result, fibers made from tricot possess characteristic properties of both terylene and cotton.

Crisis Of Artificial Polymer

Man-made polymers or artificial polymers are widely used for various purposes. The main advantage of using them is that they are durable i.e. have a long life.

But the same durability properties which make plastics ideal for so many applications can lead to waste disposal problems because these materials are not readily biodegradable.

By the word non-biodegradable, it means that they do not undergo degradation by living organisms such as microbes, bacteria, fungi, etc. Because of their resistance to biodegradation, they accumulate in the environment.

In urban areas, it can lead to several problems such as blocking the drains and sewer lines. Poly bags, plastic pouches, etc.

made of such artificial, non-biodegradable polymers lying scattered here and there has become a very common scenario in almost every city and village of our country.

Efforts to tide over the crisis: Researchers are trying to develop biodegradable polymers to suit our needs.

Biodegradable polymers are a specific type of polymer that is decomposed naturally by environmental microorganisms after their intended use.

Cellulose is one such polymeric carbohydrate that is biodegradable. It is the main constituent of the fiber of cotton and straw.

These polymeric carbohydrates are decomposed in nature by microorganisms such as fungi and bacteria.

As a result, large polymer molecules are degraded to smaller molecules which are required for the growth of those micro-organisms which degrade the polymer.

Proteins are also polymers or more appropriately, macromolecules. They are present in pieces of meat and fish. They are degraded by some specific enzymes produced by some particular bacteria.

Cellulose-based polymers, chitosan-based polymers, and starch-based polymers are all examples of biodegradable polymers. Efforts are going on to prepare biodegradable polymers with desired chemical and mechanical properties, which are non-toxic and can be naturally decomposed.