UNIT 13 HYDROGEN
Position of hydrogen in periodic table, isotopes, preparation, properties and uses of hydrogen;
----------------
Period 1 Group 1
Atomic Number 1
Symbol H
Atomic Weight 1.0079
Discovery Cavendish, 1766
Hydrogen was prepared for many years before it was recognized as a distinct element.
Electron Configuration 1s¹
Word Origin Greek: hydro, water; genes, forming
Named by Lavoisier.
Isotopes
Protium (0 neutrons), Deuterium (1 neutron), and Tritium (2 neutrons).
Properties
Hydrogen is the most abundant element in the universe.
Hydrogen is a colorless, odorless, combustible gas.
Hydrogen gas is so light and diffusive that uncombined hydrogen can escape from the atmosphere.
Hydrogen gas ordinarily is a mixture of two molecular forms, ortho- and para-hydrogen, which differ by the spins of their electrons and nuclei.
Normal hydrogen at room temperature consists of 25% of the para form and 75% of the ortho form. The ortho form cannot be prepared in the pure state. Since the two forms of hydrogen differ in energy, their physical properties also differ.
Uses
Hydrogen is important in the proton-proton reaction and carbon-nitrogen cycle. Liquid hydrogen is used in cryogenics and in the study of superconductivity.
Great quantities are used for the fixation of nitrogen from the air in the Haber ammonia process.
Hydrogen is use in welding, for the hydrogenation of fats and oils, in methanol production, in hydrodealkylation, hydrocracking, and hydrodesulfurization.
Other applications include producing rocket fuel, filling balloons, making fuel cells, producing hydrochloric acid, and reducing metallic ores.
Deuterium is used as a moderator to slow down neutrons and as a tracer.
Tritium is used in the production of the hydrogen (fusion) bomb.
Tritium is also used in making luminous paints and as a tracer.
Sources
Hydrogen occurs in the free state in volcanic gases and some natural gases. Hydrogen is prepared by steam on heated carbon, decomposition of certain hydrocarbons with heat, action of sodium or potassium hydroxide on aluminum electrolysis of water, or displacement from acids by certain metals.
Wednesday, February 13, 2008
AIEEE Chemistry Unit 13B Water and Heavy Water
Physical and chemical properties of water and heavy water;
Heavy water is water that contains the heavy isotope of hydrogen called deuterium (chemical symbol D). The deuterium atom weighs about twice as much as ordinary hydrogen atom. Heavy water, also called deuterium oxide, makes up about 1 part in 5000 of ordinary water.
It was first separated from ordinary water in 1932 by G N Lewis, a chemist at the University of California.
Because of the difference between the weights of the two kinds of hydrogen atoms, the physical properties of heavy water differ from those of ordinary water. Heavy water freezes at 3.82oC and boils at 101.42oC.
Ice made from heavy water sinks in normal water.
Heavy water is useful in some kinds of nuclear reactors. It acts as a moderator to control the energy of the neutrons in a chain reaction. Seeds will not germinate in heavy water, and some animals, including tadpoles, cannot live in it.
Heavy water is water that contains the heavy isotope of hydrogen called deuterium (chemical symbol D). The deuterium atom weighs about twice as much as ordinary hydrogen atom. Heavy water, also called deuterium oxide, makes up about 1 part in 5000 of ordinary water.
It was first separated from ordinary water in 1932 by G N Lewis, a chemist at the University of California.
Because of the difference between the weights of the two kinds of hydrogen atoms, the physical properties of heavy water differ from those of ordinary water. Heavy water freezes at 3.82oC and boils at 101.42oC.
Ice made from heavy water sinks in normal water.
Heavy water is useful in some kinds of nuclear reactors. It acts as a moderator to control the energy of the neutrons in a chain reaction. Seeds will not germinate in heavy water, and some animals, including tadpoles, cannot live in it.
Unit 13C Hydrogen Peroxide
Structure, preparation, reactions and uses of hydrogen peroxide;
Hydrogen peroxide, H2O2, was first discovered by Thenard among others in 1818 by reacting acids with barium peroxide, BaO2.
It resembles water in appearance being colourless in small quantities but blue when observed in thick layers.
It decomposes to oxygen and water and this decomposition is promoted by heat and alkalis.
Commercial grade H2O2 usually contains small amounts of stabilizers.
Hydrogen peroxide is a strong oxidising agent and is widely used as a bleaching agent. In dilute solutions it is an efficient antiseptic. The uses of hydrogen peroxide have been changing in recent years.
Uses
Textile bleaching
Chemical production
Wood pulp bleaching - Major user
Environmental uses
Miscellaneous uses
Production process
Hydrogen peroxide is produced by reducing alkylanthraquinone with hydrogen in the presence of a catalyst to the hydroquinone. After the catalyst has been removed to prevent decomposition of the hydrogen peroxide, the hydroquinone is oxidised, usually with air, back to quinone with a resultant co-production of hydrogen peroxide.
The hydrogen peroxide is removed and purified and the quinone is regenerated and returned to the reaction.
The anthraquinone must be dissolved in a suitable solvent for the hydrogenation, oxidation and extraction steps - this is usually referred to as the working solution. The solvent is usually a mixture because quinones dissolve readily in non-polar aromatic solvents, such as alkylbenzene, whereas hydroquinones dissolve well in polar solvents, such as alcohols and esters. A variety of different mixtures are in use but the aim is to satisfy a number of criteria, namely good solubility of both quinone and hydroquinone, good stability in both hydrogenator and oxidiser, low solubility in water and aqueous hydrogen peroxide solutions, sufficiently higher or lower density than water to ensure separation of the two phases during extraction, low volatility, high distribution coefficient for hydrogen peroxide in the solvent-water system and low toxicity. 1
In the hydrogenator, the working solution is reacted with hydrogen in the presence of a catalyst. The process is exothermic and the heat of reaction is removed by cooling the working solution before it enters the hydrogenator, by cooling the reactor during hydrogenation and/or by cooling the hydrogenated working solution.
After the hydrogenation reaction, the working solution must pass through a filtration stage to remove all traces of catalyst. Even small traces of catalyst in the oxidation and extraction stages lead to significant losses of hydrogen peroxide and could present safety problems. During the oxidation stage, air is passed through the hydrogenated working solution to convert the dissolved hydroquinones to quinones and form the hydrogen peroxide. The air outlet is passed over activated carbon adsorbers to recover solvent.
Crude hydrogen peroxide is extracted from the oxidised working solution by treating with water. The working solution is then regenerated and fed back to the front of the process and the crude hydrogen peroxide (15-35 wt%) is fed to a treatment unit where the concentration is increased to 50-70 wt%.
Hydrogen peroxide, H2O2, was first discovered by Thenard among others in 1818 by reacting acids with barium peroxide, BaO2.
It resembles water in appearance being colourless in small quantities but blue when observed in thick layers.
It decomposes to oxygen and water and this decomposition is promoted by heat and alkalis.
Commercial grade H2O2 usually contains small amounts of stabilizers.
Hydrogen peroxide is a strong oxidising agent and is widely used as a bleaching agent. In dilute solutions it is an efficient antiseptic. The uses of hydrogen peroxide have been changing in recent years.
Uses
Textile bleaching
Chemical production
Wood pulp bleaching - Major user
Environmental uses
Miscellaneous uses
Production process
Hydrogen peroxide is produced by reducing alkylanthraquinone with hydrogen in the presence of a catalyst to the hydroquinone. After the catalyst has been removed to prevent decomposition of the hydrogen peroxide, the hydroquinone is oxidised, usually with air, back to quinone with a resultant co-production of hydrogen peroxide.
The hydrogen peroxide is removed and purified and the quinone is regenerated and returned to the reaction.
The anthraquinone must be dissolved in a suitable solvent for the hydrogenation, oxidation and extraction steps - this is usually referred to as the working solution. The solvent is usually a mixture because quinones dissolve readily in non-polar aromatic solvents, such as alkylbenzene, whereas hydroquinones dissolve well in polar solvents, such as alcohols and esters. A variety of different mixtures are in use but the aim is to satisfy a number of criteria, namely good solubility of both quinone and hydroquinone, good stability in both hydrogenator and oxidiser, low solubility in water and aqueous hydrogen peroxide solutions, sufficiently higher or lower density than water to ensure separation of the two phases during extraction, low volatility, high distribution coefficient for hydrogen peroxide in the solvent-water system and low toxicity. 1
In the hydrogenator, the working solution is reacted with hydrogen in the presence of a catalyst. The process is exothermic and the heat of reaction is removed by cooling the working solution before it enters the hydrogenator, by cooling the reactor during hydrogenation and/or by cooling the hydrogenated working solution.
After the hydrogenation reaction, the working solution must pass through a filtration stage to remove all traces of catalyst. Even small traces of catalyst in the oxidation and extraction stages lead to significant losses of hydrogen peroxide and could present safety problems. During the oxidation stage, air is passed through the hydrogenated working solution to convert the dissolved hydroquinones to quinones and form the hydrogen peroxide. The air outlet is passed over activated carbon adsorbers to recover solvent.
Crude hydrogen peroxide is extracted from the oxidised working solution by treating with water. The working solution is then regenerated and fed back to the front of the process and the crude hydrogen peroxide (15-35 wt%) is fed to a treatment unit where the concentration is increased to 50-70 wt%.
Friday, February 1, 2008
Thursday, January 31, 2008
AIEEE Chemistry Unit 14A S-Block Elements
ALKALI AND ALKALINE EARTH METALS
Group - 1 and 2 Elements:
General introduction, electronic configuration and general trends in physical and chemical properties of elements,
The alkali metals are the elements located in Group IA of the periodic table.
The alkali metals have many physical properties common to metals, but their densities are lower than those of other metals.
Alkali metals have one electron in their outer shell.
This gives them the largest atomic radii of the elements in their respective periods.
Their low ionization energies result in their metallic properties and high reactivities.
An alkali metal can easily lose its valence electron to form the univalent cation.
Alkali metals have low electronegativities.
They react readily with nonmetals, particularly halogens.
ALKALINE EARTH METALS
The six alkaline earth metals—beryllium, magnesium, calcium, strontium, barium, and radium—comprise Group 2 on the periodic table of elements.
They are in Group 2 beside the alkali metals in Group 1, and as their names suggest, the two families share a number of characteristics, most notably their high reactivity.
Magnesium and calcium have a number of uses, ranging from building and other structural applications to dietary supplements.
In fact, both are significant components in the metabolism of living things—including the human body.
Barium and beryllium have numerous specialized applications in areas from jewelry to medicine, while strontium is primarily used in fireworks.
Radium, has radioactive qualities.
Group - 1 and 2 Elements:
General introduction, electronic configuration and general trends in physical and chemical properties of elements,
The alkali metals are the elements located in Group IA of the periodic table.
The alkali metals have many physical properties common to metals, but their densities are lower than those of other metals.
Alkali metals have one electron in their outer shell.
This gives them the largest atomic radii of the elements in their respective periods.
Their low ionization energies result in their metallic properties and high reactivities.
An alkali metal can easily lose its valence electron to form the univalent cation.
Alkali metals have low electronegativities.
They react readily with nonmetals, particularly halogens.
ALKALINE EARTH METALS
The six alkaline earth metals—beryllium, magnesium, calcium, strontium, barium, and radium—comprise Group 2 on the periodic table of elements.
They are in Group 2 beside the alkali metals in Group 1, and as their names suggest, the two families share a number of characteristics, most notably their high reactivity.
Magnesium and calcium have a number of uses, ranging from building and other structural applications to dietary supplements.
In fact, both are significant components in the metabolism of living things—including the human body.
Barium and beryllium have numerous specialized applications in areas from jewelry to medicine, while strontium is primarily used in fireworks.
Radium, has radioactive qualities.
AIEEE Chemistry Unit 14C Compounds of Sodium
Preparation and properties of some important compounds - sodium carbonate, sodium chloride, sodium hydroxide and sodium hydrogen carbonate;
Sodium carbonate (Na2CO3)
Sodium carbonate exists as anhydrous (Na2CO3) and also as hydrated salt. The decahydrated salt (Na2CO3.10H2O) is known as washing soda while the anhydrous salt is called soda ash.
Occurrence
Large deposits of this salt occur in Owens lake in California and Lake Magadi in British East Africa. It occurs native as Na2CO3.NaHCO3.H2O in Egypt.
During hot weather, soda is also collected from a large number of alkaline lakes.
Manufacture of Sodium Carbonate
Ammonia-soda process (or Solvay process)
This process is the most popularly used method. As Ernest Solvay, the Belgian chemical engineer, devised it in 1864 it is known as Solvay process.
Raw materials
The raw materials for this process are common salt, ammonia and limestone (for supplying CO2 and quicklime).
Principle
When carbon dioxide is passed into a concentrated solution of brine saturated with ammonia, ammonium bicarbonate is produced,
The ammonium bicarbonate then reacts with common salt forming sodium bicarbonate,
Sodium bicarbonate being slightly soluble (in presence of sodium ions) gets precipitated. The precipitated sodium bicarbonate is removed by filtration and changed into sodium carbonate by heating.
The mother liquor remaining after the precipitation of sodium bicarbonate contains ammonium chloride. This is used to regenerate ammonia (one of the raw materials) by steam heating with milk of lime.
Lime is obtained by heating limestone.
Ammonia and carbon dioxide liberated are utilized in making the whole process cyclic and continuous. The only by-product in the process is calcium chloride.
Sodium chloride (NaCl)
Sodium chloride (NaCl) or common salt is an ionic crystal consisting of equal numbers of sodium and chlorine atoms and is an essential component in the human diet, being found in blood sweat and tears.
Occurrence
Sodium chloride is abundant and can be found naturally occurring. It can be found in the mineral halite (pure rock salt) as well as in mixed evaporates in salt lakes.
Sea water also contains 2.7% by weight salt and constitutes 80% of the dissolved minerals in sea water.
Production
Sodium chloride is mined or obtained from brine, when water is added to salt deposits.
Alternatively, it is obtained from sea water. This is commonly known as sea salt and constitutes most table salt. It also contains some impurities.
Sodium chloride:
• Has a cubic crystalline structure
• Is clear when pure, although may also appear white, grey or brownish, depending upon purity
• Is soluble in water
• Is slightly soluble in other liquids
• Is odourless
• Has a characteristic taste
• Molten sodium chloride is an electrical conductor
Symbol NaCl
Atomic Weight 58.44
Eutectic Composition 23.31% NaCl
Melting Point 801°C
Boiling Point 1465°C
Density 2.17g/cm3
Refractive Index 1.5442
Mohs Hardness 2.5
Co-Efficient of Thermal Expansion @ 0°C 40x10-6
Solubility g/100g H2O at 0°C 35.7
Sodium chloride is used for:
• Windows for analytical instruments
• De-icing
• Food and cooking
• High power lasers
• To produce chlorine and sodium
• Historically it has been used as a form of currency
Sodium hydroxide
sodium hydroxide chemical compound, NaOH, is a white crystalline substance that readily absorbs carbon dioxide and moisture from the air.
It is very soluble in water, alcohol, and glycerin.
It is a caustic and a strong base
It is commonly known as caustic soda, lye, or sodium hydrate.
The principal method for its manufacture is electrolytic dissociation of sodium chloride; chlorine gas is a coproduct.
Small amounts of sodium hydroxide are produced by the soda-lime process in which a concentrated solution of sodium carbonate (soda) is reacted with calcium hydroxide (slaked lime); calcium carbonate precipitates, leaving a sodium hydroxide solution.
The major use of sodium hydroxide is as a chemical and in the manufacture of other chemicals; because it is inexpensive, it is widely used wherever a strong base is needed.
It is also used in producing rayon and other textiles, in making paper, in etching aluminum, in making soaps and detergents, and in a wide variety of other uses.
Sodium Bicarbonate NaHCO-3
Sodium Bicarbonate, commonly called baking soda, is a white odourless, crystalline solid, completely soluble in water but slightly soluble in ethanol. It is the mildest of all sodium alkalis.
It is prepared from purified sodium carbonate or sodium hydroxide solution with passing carbon dioxide which is bubbled into the solution of pure carbonate, and the bicarbonate precipitates out to be dried as the bicarbonate is less soluble than the carbonate.
Sodium bicarbonate is also made as an intermediate product in the Solvay process (described above)which is to make sodium carbonate from calcium carbonate by treating sodium chloride with ammonia and carbon dioxide.
The major use of sodium bicarbonate is in baking powders.
Sodium Bicarbonate plays an important role in the products of many diverse industries with functions of releasing CO2 when heated above about 50 C or when reacted with a weak acid makes sodium bicarbonate a key ingredient in food leavening as well as in the manufacture of effervescent salts and beverages.
It can react as an acid or a base in water treatment.
In health and beauty applications, mild abrasivity and ability to reduce odors chemically by neutralizing the acid by-products of bacteria are utilized.
It is also used in treating wool and silk, fire extinguishers, pharmacy, leather, oredressing, metallurgy, in cleaning preparations and industrial & chemical processe.
Uses
food & food processing, beverages , pharmaceuticals , animal foodstuffs , household cleaning products , rubber & plastics foam blowing , fire extinguishers & explosion suppression , effluent & water treatment, flue gas treatment , oil drilling , industrial & chemical processes
Sodium carbonate (Na2CO3)
Sodium carbonate exists as anhydrous (Na2CO3) and also as hydrated salt. The decahydrated salt (Na2CO3.10H2O) is known as washing soda while the anhydrous salt is called soda ash.
Occurrence
Large deposits of this salt occur in Owens lake in California and Lake Magadi in British East Africa. It occurs native as Na2CO3.NaHCO3.H2O in Egypt.
During hot weather, soda is also collected from a large number of alkaline lakes.
Manufacture of Sodium Carbonate
Ammonia-soda process (or Solvay process)
This process is the most popularly used method. As Ernest Solvay, the Belgian chemical engineer, devised it in 1864 it is known as Solvay process.
Raw materials
The raw materials for this process are common salt, ammonia and limestone (for supplying CO2 and quicklime).
Principle
When carbon dioxide is passed into a concentrated solution of brine saturated with ammonia, ammonium bicarbonate is produced,
The ammonium bicarbonate then reacts with common salt forming sodium bicarbonate,
Sodium bicarbonate being slightly soluble (in presence of sodium ions) gets precipitated. The precipitated sodium bicarbonate is removed by filtration and changed into sodium carbonate by heating.
The mother liquor remaining after the precipitation of sodium bicarbonate contains ammonium chloride. This is used to regenerate ammonia (one of the raw materials) by steam heating with milk of lime.
Lime is obtained by heating limestone.
Ammonia and carbon dioxide liberated are utilized in making the whole process cyclic and continuous. The only by-product in the process is calcium chloride.
Sodium chloride (NaCl)
Sodium chloride (NaCl) or common salt is an ionic crystal consisting of equal numbers of sodium and chlorine atoms and is an essential component in the human diet, being found in blood sweat and tears.
Occurrence
Sodium chloride is abundant and can be found naturally occurring. It can be found in the mineral halite (pure rock salt) as well as in mixed evaporates in salt lakes.
Sea water also contains 2.7% by weight salt and constitutes 80% of the dissolved minerals in sea water.
Production
Sodium chloride is mined or obtained from brine, when water is added to salt deposits.
Alternatively, it is obtained from sea water. This is commonly known as sea salt and constitutes most table salt. It also contains some impurities.
Sodium chloride:
• Has a cubic crystalline structure
• Is clear when pure, although may also appear white, grey or brownish, depending upon purity
• Is soluble in water
• Is slightly soluble in other liquids
• Is odourless
• Has a characteristic taste
• Molten sodium chloride is an electrical conductor
Symbol NaCl
Atomic Weight 58.44
Eutectic Composition 23.31% NaCl
Melting Point 801°C
Boiling Point 1465°C
Density 2.17g/cm3
Refractive Index 1.5442
Mohs Hardness 2.5
Co-Efficient of Thermal Expansion @ 0°C 40x10-6
Solubility g/100g H2O at 0°C 35.7
Sodium chloride is used for:
• Windows for analytical instruments
• De-icing
• Food and cooking
• High power lasers
• To produce chlorine and sodium
• Historically it has been used as a form of currency
Sodium hydroxide
sodium hydroxide chemical compound, NaOH, is a white crystalline substance that readily absorbs carbon dioxide and moisture from the air.
It is very soluble in water, alcohol, and glycerin.
It is a caustic and a strong base
It is commonly known as caustic soda, lye, or sodium hydrate.
The principal method for its manufacture is electrolytic dissociation of sodium chloride; chlorine gas is a coproduct.
Small amounts of sodium hydroxide are produced by the soda-lime process in which a concentrated solution of sodium carbonate (soda) is reacted with calcium hydroxide (slaked lime); calcium carbonate precipitates, leaving a sodium hydroxide solution.
The major use of sodium hydroxide is as a chemical and in the manufacture of other chemicals; because it is inexpensive, it is widely used wherever a strong base is needed.
It is also used in producing rayon and other textiles, in making paper, in etching aluminum, in making soaps and detergents, and in a wide variety of other uses.
Sodium Bicarbonate NaHCO-3
Sodium Bicarbonate, commonly called baking soda, is a white odourless, crystalline solid, completely soluble in water but slightly soluble in ethanol. It is the mildest of all sodium alkalis.
It is prepared from purified sodium carbonate or sodium hydroxide solution with passing carbon dioxide which is bubbled into the solution of pure carbonate, and the bicarbonate precipitates out to be dried as the bicarbonate is less soluble than the carbonate.
Sodium bicarbonate is also made as an intermediate product in the Solvay process (described above)which is to make sodium carbonate from calcium carbonate by treating sodium chloride with ammonia and carbon dioxide.
The major use of sodium bicarbonate is in baking powders.
Sodium Bicarbonate plays an important role in the products of many diverse industries with functions of releasing CO2 when heated above about 50 C or when reacted with a weak acid makes sodium bicarbonate a key ingredient in food leavening as well as in the manufacture of effervescent salts and beverages.
It can react as an acid or a base in water treatment.
In health and beauty applications, mild abrasivity and ability to reduce odors chemically by neutralizing the acid by-products of bacteria are utilized.
It is also used in treating wool and silk, fire extinguishers, pharmacy, leather, oredressing, metallurgy, in cleaning preparations and industrial & chemical processe.
Uses
food & food processing, beverages , pharmaceuticals , animal foodstuffs , household cleaning products , rubber & plastics foam blowing , fire extinguishers & explosion suppression , effluent & water treatment, flue gas treatment , oil drilling , industrial & chemical processes
Thursday, January 24, 2008
AIEEE Chemistry Unit 15A P Block Elements
Group - 13 to Group 18 Elements
General Introduction: Electronic configuration and general trends in physical and chemical properties of elements across the periods and down the groups; unique behaviour of the first element in each group.
General Introduction: Electronic configuration and general trends in physical and chemical properties of elements across the periods and down the groups; unique behaviour of the first element in each group.
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