EARTH CHEMISTRY

Chemical composition of the crust

• The crust of the earth composed of three principal types of rocks igneous, sedimentary and metamorphic. The 8 elements make up almost 99% of the earth’s crust.
• Oxygen is the most abundant element by weight and accounts for more than 90% of the volume of the crust. Next in the sequence is silicon.
• In the most abundant element’s list, everyday common elements like carbon, copper, zinc and nitrogen do not appear among the 10 most abundant elements.
• Chemical Composition of the atmosphere
• The hydrosphere is composed of water, along with snow and ice. There is about 273 liters of water for each square cm of the earth’s surface. Of this water, 286.4 liters if ocean. 0.1 litres is freshwater and 4.5 litres is ice & snow. The earth’s atmosphere, is made up of a number of gases, which are
• Nitrogen (N2)        -           78.1%
• Oxygen (O2)                     -           20.29%
• CO2                                              -           0.3%
• Water vapour                   -           0.4%
• Inert gases                         -           0.95%
• SO2, N2O, etc.      -           Variable
• The N2 in the air, control the O2 in the air, as O2 is very reactive. Without N2, everything will be burning in the atmosphere. N2 also helps in plant growth & protein formation. CO2 is utilized by the plants to prepare food during the photosynthesis. Water vapour controls the evaporation of water from the bodies of plants & animals. Air is also required for burning and combustion. O2 is essential for respiration. The amount of O2, N2 and CO2 remains the same.

ELEMENTS, MOLECULES & COMPUNDS

• An element is a substance, which can neither be broken nor build from two or more simple substances.105 elements are known today.
• A compound is a substance, which is made up of two or more elements, combined in fixed proportion by weight, and is decomposable into constituents through any method.
• A mixture is obtained by mixing any two elements or compounds in any proportion. It may be homogenous or heterogeneous.

Structure of the atom

• John Dalton put the theory that the all matter is made up of atoms. According to him; the atom is smallest particle of matter and may have independent existence. According to, modern atomic theory, an atom is made up of three particles protons, neutrons and electrons.
• An atom is neutral, as the number of protons and electrons are the same.
• The nucleus, is the central part of the atom, and is embedded with proton and neutrons. The electrons surround the nucleus, and lie in orbits & are in continuous motion.
• The distribution of electrons in the orbits is called the electronic configuration.
• The atomic weight equals the total number of protons & neutrons. The atomic number of atom equals the total number of electrons.
• Atomic Weight  =  No. of Protons + No. of Neutrons
• Atomic Number =  No. of Electrons = No. of Protons
• No. of Proton   =  Atomic Weight – No. of Neutrons

PERIODIC TABLE OF ELEMENTS

• D.I Mendeleev was the first person, which devised the periodic table of elements. According to him, elements can be arranged according to their atomic weight, and will show periodicity of the properties. All elements were arranged according to their atomic weights in horizontal and vertical columns.There are seven periods (horizontal columns) and 18 groups (vertical columns).The vertical columns were further subdivided into sub-groups, thus numbered 1A-7A, 1B-7B, 8 and O groups,
• All properties of all elements in a one subgroup are same. According to Modern Periodic Table, all elements are arranged according to the atomic numbers, and groups & sub groups are alike with Mendeleev’s Periodic Table.
• Some important elements and their uses
• Helium: it is used as gas in air ships & balloons. Helium is mixed with O2 to inhale during sea diving; also used in welding of metals.
• Lithium: Its various compound are used as drugs for mental depression (Li2CO3), also used gout & rheumatism (lithium salicylate, lithium benzoate & citrate); to produce thermonuclear energy.
• Beryllium: Beryllium with other metals form alloys, having high strength.
• Fluorine: It is used to manufacture uranium hexa-floride (UF6) to generate nuclear power; in Ferons, fluorine is used as refrigerants or aerosols. Cryolite is used in aluminium making.
• Sodium: It forms an antiknock alloy with lead. It is also used as heat exchanger in nuclear reactions.
• Magnesium: This element is used for flash powers. It forms duralium metal with aluminium and used for aeroplane making.
• Potassium: It is used in photovoltaic cells & Na-K alloy are used in high temperature thermometers.
• Titanium: It is used to resist corrosion. Ti steel is utilized in making of supersonic aircrafts, jet engines, turbine engines; it hardens and steel.
• Vanadium: Ferro-vanadium alloy are specially used to make steels.
• Chromium: used with steel to produce special steels like chrome-chrome & stainless steels.
• Manganese: It is used to manufacture Mn steel; Mn in steel imparts hardness & toughness, which are used in making of rock crushers etc.
• Cobalt: It makes alloys like steel, and used to make permanent magnets, to make cutting tools, surgical instruments; also used electroplating.

• Arsenic: Arsenic compounds are useful for weed killing.
• Selenium: is used in photovoltaic cells.
• Strontium: Strontium is used to recover sugar from molasses.
• Zirconium: is used to make bulletproof clothes.
• Molybdenum: Molybdenum steel with nickel is used to make the gun barrels.
• Palladium: is alloyed with gold which serves as substitute for platinum
• Cadmium: Cadmium rods are used in the nuclear reactors; it makes fusible alloys such as wood’s metal, rose metal.
• Tin: It is utilized in making of such alloys: solder Britannia metal, white metal, bell metal, rose metal & solder etc.
• Tungsten: wires used to make filaments of the electrical appliances.
• Platinum: It is inert to oxygen and water thus utilized to made crucibles etc.
• Bismuth: It is employed to make fusible alloys, to make automatic electrical fuses, automatic fire alarms etc.

HYDROGEN AND WATER

• Water is abundant in all chemical substances.It is very important for life, and all organic life have 50 to 70% of water.Water exists in all three kinds of matter solid, liquid and gas.Water is a universal solvent except a few substances. It has importance in agriculture, industry including chemical.A drinking water contains small amounts of different salts and gases.Rainwater is the purest form of the natural water.

Hydrogen has three types of isotopes

• The Proteium isotope is the most abundant of all the hydrogen isotopes (up to 99.985%).
• Tritium has a half-life of 12.35 years, formed due to nuclear reactions induced by the cosmic rays in the atmosphere.
• Heavy water (D2O) - is used as moderator in the nuclear reactors to slow down the fast moving neutrons.
• Hydrogen occurs in the nature in large amounts in water, acids, carbohydrates, plants and animals proteins, vitamins, wood, coal tar, oil & natural gas etc.
• Hydrogenation is process, during which the vegetable oil in the presence of catalyst (nickel) is converted into vegetable ghee.
• Water is the principal constituent 75% of earth’s surface and is an essential component of plants and animals in life processes.
• It constitutes about 65% of the human body and up to 95% of many plants.
• Water molecule is a bent molecule with a bond angle of 104.5.
• Water is a substance of great complexity.
• Water is a good solvent of ionic compounds due to its maximum dielectric constant i.e. is 80 hence known as universal solvent.
• A number of ionic compounds like silver chloride, calcium fluoride, barium Sulphate and aluminium trifloride, are non soluble in water.
• Some carbon compounds such as alcohols, carboxylic acids and carbohydrates does not dissolve in water.

Soft and Hard Water

• Soft water is either pure water (e.g. rain water), or soft water in which the dissolved impurities (e.g. sodium salts) do not hinder its lather forming property. Soft water forms rich lather with soaps immediately.
• Hard water does not lather with soaps immediately. It is due to presence of some salts in water (mainly calcium and magnesium salts)
• Hard water is objectionable for many uses, particularly for washing, bathing or making steam in the industries. If hard water used in the industries. It leads to the formation of deposits in the boilers.
• A number of methods are generally employed for softening of water (i.e. converting the hard water into soft water). The hardness of water is of two types: -

Temporary hardness

• It can be removed by boiling the water. It is due to the presence of bicarbonates of calcium or magnesium. On boiling, these bicarbonates decompose, and insoluble carbonates are removed by the filtration.
• It can also be removed by addition of a calculated amount of lime (calcium hydroxide)

Permanent hardness

• It is due to presence of soluble calcium or magnesium salts (others than bicarbonates). From this type water hardness can be removed by precipitation (use of washing soda), by exchange of Ca, Mg ions with sodium ions in the zeolities. With use of calgon, the renders Ca & Mg ions ineffective.

Hydrogen peroxide

• Hydrogen peroxide is utilized in bleaching of wool and hair. In medicine, it is used as disinfectant. It is utilized in restoration of old parting in which lead oxide has been used as a white paint.
• White lead in these paintings changes into black lead Sulphide on exposure to atmosphere. Hydrogen peroxide is used to oxidize black lead Sulphide to white lead Sulphate.
• Hydrogen peroxide is used as a propellant for torpedoes. Concentrated hydrogen peroxide is now finding an important use as an oxidant for rocket fuel.

CARBON AND ITS COMPOUDS

• Carbon is the most abundant element on the earth. Carbon is most useful to the mankind, as it has served men with various ways-food material, fuels, cloths and drugs, which are made up of carbon compounds.
• Its various allotropic forms are diamond, graphite, coal, coke, etc. and each form is characterized by individual physical and chemical properties.
• Diamond is the most purest form of carbon, and are formed due to crystallization of carbon. The structure of diamond is a 3-D polymeric, in the form of tetrahedron, which makes the diamond one of the hardest material.
• Graphite is softest form of carbon, consists of sheets of carbon and which are atom, held together by vertical covalent bonds.
• CO2 is present in the atmosphere with a concentration of 325 ppm. A natural equilibrium is maintained in level of CO2 in the atmosphere by photosynthesis & precipitation in form of carbonates, deposited as carbonate rocks and are it is also produced by combustion of organic matters.
• In recent times concentration of CO2 has increased considerably after Industrial Revolution, and is one of cause for the greenhouse effect.
• The carbon monoxide (CO) has very small amount in the atmosphere, and is produced during the combustion of oil in an automobile engine, or during when fuel is burned in a closed room.
• CO is a colourless, odourless gas, and is a poisonous gas.
• Its poisonous nature is due to the fact that combines with the haemoglobin of the blood, and forms indecomposable carboxy-haemoglobin, thus affecting oxygen carrying ability of the haemoglobin; this disorder is known as asphyxiation.
• The carbon cycle maintains the level of CO2 in the environment, between production & consumption at a constant (0.04%) rate.

NITROGEN AND ITS COMPOUNDS

• It is very essential for life; as it controls over-reactive oxygen in the air and in the form of protein & nucleic acid form a basis of life.
• Ammonia is an important compound of nitrogen and is obtained commercially by the Haber’s process. Ammonia is used as a refrigerant, manufacture of fertilizers, medicines and others.
• Nitrogen is an essential constituent of the plant and animal life. Animal gets nitrogen supply from plant and plants get it from the soil.
• The nitrogen cycle maintains the nitrogen level in the environment. The blue green algae are adaptable enough to convert the atmospheric nitrogen into nitrogenous compounds.

COMPUNDS OF ALMINIUM

• Aluminum Hydride: As catalyst for polymerizations; reducing agent
• Aluminum Oxide: Used as a abrasive for ceramic materials, electric insulators and resistors, dental cements, glass, steel, artifical gems, and in coating for metals.
• Aluminum Bromide: Used as an acid catalyst in organic syntheses.
• Aluminum Fluoride:  Used in ceramics, as fluz in matallurgy, in aluminum manufacture, as inhibotor of fermentation, as catalyst in organic reactions.
• Aluminum Chloride: Used in cracking of petroleum, in manufacture of rubbers and lubicants.Also used in slaughter houses as a disinfectant and in deordants. I think that this is a very important compound for people around the world.
• Aluminum Iodide: Catalyst in organic reactions

METALS AND ITS EXTRACTION

• Metals are found in nature in the form of minerals or oreas. The native minerals are the metals occurring in a free state e.g. cooper, silver, gold etc. A mineral is composed of naturally occurring metals.
• An ore is a mineral, from which metal can be extracted economically. Extration of a metal from an ore involves following steps.

  i)     Beneficiation (concentration of the ore) in this process, ore is usually crushed and grounded until all the particles are broken down. The unwanted material (gangue) is removed using the washing, foam flotation process, magnetic separation, based upon difference between the ore and gangue.

  ii)    Conversion of concentrated ore into simpler compounds- carbonated ores is converted into metal oxides by calcination and sulphide ores are converted into metal oxides by roasting.

  iii)   Reduction of metal oxide: The metal oxides are reduced to meal by carbon, aluminum or electrolyte, reduction.

  iv)   Refining of the impure metal: Refining is done to purify the metal, and is performed by electrolysis, liquation, distillation and oxidation methods

Ores of some important elements

• Lithium                 Lithium mica, Petalite, Spodumene
• Sodium                Common salt (rock salt), Chile saltpetre, Cryolite,
• Beryllium              Beryl
• Magnesium           Dolomite, Carnallite,     Asbestos
• Calcium                Limestone, Chalk, Calcite, Marble, Dolomite, Stalactite, Stalagmite
• Radium                 Pitch blende, Carnotite
• Aluminium           Bauxite, Cryolite, Corundum
• Tin                         Cassiterite, Tinstone
• Lead                      Galena
• Phosphorous         Phosphorite, Apatite ,   Chlorple
• Sulphur                 Native sulphur
• Titanium               Rutile, Ilmente
• Chromium            Chromite
• Molybdenum         Molybdenite, Wulfranite
• Tungsten               Wolframite, Sheelite
• Manganese            Pyrolusite, Braunite,     Hausmantite
• Iron                                               Haematite, Magnetite, Siderite
• Cobalt                               Cobalitite
• Nickel                               Pentlendite, Garnierite,Kupfer’s nickel
• Copper                  Copperpyrite, Cuperite,Malachite
• Silver                                Silver glance (Argentite),          Horn silver, Ruby silver ,          (pyrargrite)
• Zinc                                  Zinc blende, Calamine
• Thorium                Monazite, Thorite

ALLOY

• Substance composed of two or more metals. Alloys, like pure metals, possess metallic luster and conduct heat and electricity well, although not generally as well as do the pure metals of which they are formed. Compounds that contain both a metal or metals and certain nonmetals, particularly those containing carbon, are also called alloys. Important alloys include

PETROLEUM AND NATURAL GAS 

• The chemical composition of all petroleum or rock oil is principally hydrocarbons, although a few sulfur-containing and oxygen-containing compounds are usually present; the sulfur content varies from about 0.1 to 5 percent. Petroleum contains gaseous, liquid, and solid elements. The consistency of petroleum varies from liquid as thin as gasoline to liquid so thick that it will barely pour. Small quantities of gaseous compounds are usually dissolved in the liquid; when larger quantities of these compounds are present, the petroleum deposit is associated with a deposit of natural gas (see Gases, Fuel).
• Three broad classes of crude petroleum exist: the paraffin types, the asphaltic types, and the mixed-base types. The paraffin types are composed of molecules in which the number of hydrogen atoms is always two more than twice the number of carbon atoms. The characteristic molecules in the asphaltic types are naphthenes, composed of twice as many hydrogen atoms as carbon atoms. In the mixed-base group are both paraffin hydrocarbons and naphthenes

Formation

• Petroleum is formed under the earth’s surface by the decomposition of marine organisms. The remains of tiny organisms that live in the sea—and, to a lesser extent, those of land organisms that are carried down to the sea in rivers and of plants that grow on the ocean bottoms—are enmeshed with the fine sands and silts that settle to the bottom in quiet sea basins. Such deposits, which are rich in organic materials, become the source rocks for the generation of crude oil. The process began many millions of years ago with the development of abundant life, and it continues to this day. The sediments grow thicker and sink into the seafloor under their own weight. As additional deposits pile up, the pressure on the ones below increases several thousand times, and the temperature rises by several hundred degrees. The mud and sand harden into shale and sandstone; carbonate precipitates and skeletal shells harden into limestone; and the remains of the dead organisms are transformed into crude oil and natural gas.
• Once the petroleum forms, it flows upward in the earth’s crust because it has a lower density than the brines that saturate the interstices of the shales, sands, and carbonate rocks that constitute the crust of the earth. The crude oil and natural gas rise into the microscopic pores of the coarser sediments lying above. Frequently, the rising material encounters an impermeable shale or dense layer of rock that prevents further migration; the oil has become trapped, and a reservoir of petroleum is formed. A significant amount of the upward-migrating oil, however, does not encounter impermeable rock but instead flows out at the surface of the earth or onto the ocean floor. Surface deposits also include bituminous lakes and escaping natural gas.

Refining

• Once oil has been produced from an oil field, it is treated with chemicals and heat to remove water and solids, and the natural gas is separated. The oil is then stored in a tank, or battery of tanks, and later transported to a refinery by truck, railroad tank car, barge, or pipeline. Large oil fields all have direct outlets to major, common-carrier pipelines.

Basic Distillation

• The basic refining tool is the distillation unit. Crude oil begins to vaporize at a temperature somewhat less than that required to boil water. Hydrocarbons with the lowest molecular weight vaporize at the lowest temperatures, whereas successively higher temperatures are required to distill larger molecules. The first material to be distilled from crude oil is the gasoline fraction, followed in turn by naphtha and then by kerosene. The residue in the kettle, in the old still refineries, was then treated with caustic and sulphuric acid (H₂SO₄), and finally steam distilled thereafter. Lubricants and distillate fuel oils were obtained from the upper regions and waxes and asphalt from the lower regions of the distillation apparatus. In the later 19th century the gasoline and naphtha fractions were actually considered a nuisance because little need for them existed, and the demand for kerosene also began to decline because of the growing production of electricity and the use of electric lights. With the introduction of the automobile, however, the demand for gasoline suddenly burgeoned, and the need for greater supplies of crude oil increased accordingly.

Thermal Cracking

• In an effort to increase the yield from distillation, the thermal cracking process was developed. In this process, the heavier portions of the crude oil were heated under pressure and at higher temperatures. This resulted in the large hydrocarbon molecules being split into smaller ones, so that the yield of gasoline from a barrel of crude oil was increased. The efficiency of the process was limited, however, because at the high temperatures and pressures that were used, a large amount of coke was deposited in the reactors. This in turn required the use of still higher temperatures and pressures to crack the crude oil. A coking process was then invented in which fluids were recirculated; the process ran for a much longer time, with far less buildup of coke. Many refiners quickly adopted the process of thermal cracking.

Alkylation and Catalytic Cracking

• Two additional basic processes, alkylation and catalytic cracking, were introduced in the 1930s and further increased the gasoline yield from a barrel of crude oil. In alkylation small molecules produced by thermal cracking are recombined in the presence of a catalyst. This produces branched molecules in the gasoline boiling range that have superior properties—for example, higher antiknock ratings—as a fuel for high-powered engines such as those used in today’s commercial planes.
• In the catalytic-cracking process, the crude oil is cracked in the presence of a finely divided catalyst. This permits the refiner to produce many diverse hydrocarbons that can then be recombined by alkylation, isomerization, and catalytic reforming to produce high antiknock engine fuels and specialty chemicals. The production of these chemicals has given birth to the gigantic petrochemical industry, which turns out alcohols, detergents, synthetic rubber, glycerin, fertilizers, sulfur, solvents, and the feedstocks for the manufacture of drugs, nylon, plastics, paints, polyesters, food additives and supplements, explosives, dyes, and insulating materials. The petrochemical industry uses about 5 percent of the total supply of oil and gas in the U.S.

Coal Gas

• The most important coal-gasification processes aim chiefly at production of so-called pipeline quality gas, which is reasonably interchangeable with natural gas. Gas from coal, besides having pumping and heating specifications, must meet strict limits on content of carbon monoxide, sulfur, inert gases, and water. To meet these standards, most coal-gasification processes culminate with gas cleanup and methanation operations. Various hydrogasification processes, in which hydrogen reacts directly with coal to form methane, are used today; these processes bypass the indirect step of producing synthesis gas, hydrogen and carbon monoxide, before an upgrading yields methane. Other coal-gas processes include the carbon dioxide acceptor process, employing the lime-bearing material dolomite, and the molten salt process. These processes work indirectly to produce synthesis gas first. Other gases manufactured formerly from coal and coke, such as illumination gas and coke-oven gas, are of little or no importance today.

Producer and Blast-Furnace Gases

• Producer gas is a form of water gas, a term applied to steam-process gases. It is made by burning low-grade fuel (such as lignite or bituminous coal) in a closed vessel, called a producer, while passing a continuous stream of steam and air through the producer. Because of the air present in the producer, the resulting gas is approximately 50 percent incombustible nitrogen and is low in fuel value, having only about 28 percent the heating value of coke-oven gas.
• Blast-furnace gas, which results from the interaction of limestone, iron ore, and carbon in blast furnaces, has some heating value because of its carbon monoxide content but contains about 60 percent nitrogen. Enormous quantities are produced during the operation of furnaces. Most of this gas is consumed in heating the air blast and driving the compressors for the blast. The heating value of blast-furnace gas is about 16 percent of that of coke-oven gas. For a discussion of oil gas, made by the pyrolysis of petroleum hydrocarbons, See Cracking.

Natural Gas

• A certain amount of natural gas almost always occurs in connection with oil deposits and is brought to the surface together with the oil when a well is drilled. Such gas is called casing-head gas. Certain wells, however, yield only natural gas.
• Natural gas contains valuable organic elements that are important raw materials of the natural-gasoline and chemical industries. Before natural gas is used as fuel, heavy hydrocarbons such as butane, propane, and natural gasoline are extracted as liquids. The remaining gas constitutes so-called dry gas, which is piped to domestic and industrial consumers for use as fuels; dry gas, devoid of butane and propane, also occurs in nature. Composed of the lighter hydrocarbons methane and ethane, dry gas is used also in the manufacture of plastics, drugs, and dyes. Natural gas contains about 80% methane and 10% ethane, while rest is the other hydrocarbon gases. It is utilised as a domestic cooking gas, which is compressed and filled as liquefied petroleum gas (LPG) in the cylinders.

LPG

• The Liquefied Petroleum Gas (LPG) is essentially liquid butane or propane (obtained from natural gas) or butane propane mix (obtained during refining of gas or cracked gas). The fuel is highly volatile, gaseous under ordinary atmospheric situations, highly combustible and forms an explosive mixture with air.
• To detect the gas leakage, a strong smelling substance (odorous organic sulphides known as mercaptans) are added.
• Except domestic use, the LPG can be utilised in agricultural, food processing, textile, metal and ceramic purposes.
• The compressed natural gas can be utilized as engine fuel for vehicles and trucks.

Gobar Gas

• This gas is obtained by the gobar, which is subjected to anaerobic fermentation by a culture of microorganisms in closed tanks. The gas thus formed is mainly methane and CO2.The optimum temperature for the reaction is 35-55C.The residue is a excellent manure for the plant’s growth.

ELECTROLYSIS

• Electrolysis is a chemical in the metal, and results into the flow of electrons.
• The negative ions move towards the anode while the positive ions move towards the cathode.
• It is of greater significance, since it had led to the development of important technical processes associated with the production and purification of non-ferrous metals and electro synthesis of organic compounds.
• Electrolysis has found wide applications in industries and other fields.
• The electrolysis is employed in the isolation of large number of metals (Na, Al, Mg, Ca, Cu, etc.) and non-metals (Cl2, F2, etc.). And manufacture of compounds such as sodium hydroxide, heavy water & potassium permanganate.
• Electrodeposition of metals is also based on electrolysis.
• Electrolytic decomposition is the basis for a number of important extractive and manufacturing processes in modern industry. Caustic soda, an important chemical in the manufacture of paper, rayon, and photographic film, is produced by the electrolysis of a solution of common salt in water (see Alkalies). The reaction produces chlorine and sodium. The sodium in turn reacts with the water in the cell to yield caustic soda. The chlorine evolved is used in pulp and paper manufacture.
• An important industrial use of electrolysis is in the electrolytic furnace, which is employed in the manufacture of aluminum, magnesium, and sodium. In this furnace the resistance of a charge of metallic salts is used to heat the charge until it becomes molten and ionizes. The metal is then deposited electrolytically. See Electric Furnace.
• Electrolytic methods are also employed in the refining of lead, tin, copper, gold, and silver. The advantage of extracting or refining metals by electrolytic processes is that the deposited metal is of great purity. Electroplating, another industrial application of electrolytic deposition, is used to deposit films of precious metals on base metals and to deposit metals and alloys, as strengthening or wear-resistant coating, on metal parts. Recent advances in electrochemistry include the development of new techniques for placing layers of material on electrodes to increase their efficiency and endurance. Electrodes made out of polymers are now also possible, through the discovery of polymers that can conduct electricity.
• Electroplating is done to provide inert and attractive coating on metals.
• The metals most frequently used as plating materials are Cu, Ni, Cr, Zn and noble metals like silver and gold.
• It is going to play an important role in future as a source of energy.