Current Affairs UPSC

 Synthetic Fibers and Plastics   1.           Synthetic Fibres  

• A synthetic fibre is a chain of small units joined together. Each small unit is actually a chemical substance. Many such small units combine to form a large single unit called a polymer.
• Polymers occur in nature also. Cotton, for example, is a polymer called cellulose. Cellulose is made up of a large number of glucose units.
• Silk fibre obtained from silkworm was discovered in China and was kept as a closely guarded secret for a long time. Attempts were made to make silk artificially. Towards the end of the nineteenth century, scientists were successful in obtaining a fibre having properties similar to that of silk. Such a fibre was obtained by chemical treatment of wood pulp. This fibre was called rayon or artificial silk.
• Although rayon is obtained from a natural source, wood pulp, yet it is a man-made fibre. It is cheaper than silk and can be woven like silk fibres. It can also be dyed in a wide variety of colours. Rayon is mixed with cotton to make bed sheets or mixed with wool to make carpets.
• Nylon is another man-made fibre. In 1931, it was made without using any natural raw material (from plant or animal). It was prepared from coal, water and air. It was the first fully synthetic fibre.
• Nylon fibre was strong, elastic and light. It was lustrous and easy to wash. So, it became very popular for making clothes.
• We use many articles made from nylon, such as socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains etc. Nylon is also used for making parachutes and ropes for rock climbing. A nylon thread is actually stronger than a steel wire.
• Polyester is another synthetic fibre. Fabric made from this fibre does not get wrinkled easily. It remains crisp and is easy to wash. So, it is quite suitable for making dress material.
• We must have seen people wearing polyester shirts and other dresses. Terylene is a popular polyester. It can be drawn into very fine fibres that can be woven like any other yam.
• PET is a very familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products.
• Polyester (Poly+ester) is actually made up of the repeating units of a chemical called an ester. Esters are the chemicals which give fruits their smell. Fabrics are sold by names like polycot, polywool, terrycot etc. As the name suggests, these are made by mixing two types of fibres, Polycot is a mixture of polyester and cotton. Polywool is a mixture of polyester and more...

 Solutions, Osmosis, Electro - Chemistry   1.           Solutions  

• 1 part per million (ppm) of fluoride ions in water prevents tooth decay, while \[1.5\]ppm causes the tooth to become mottled and high concentrations of fluoride ions can be poisonous (for example, sodium fluoride is used in rat poison).
• Intravenous injections are always dissolved in water containing salts at particular ionic concentrations that match with blood plasma concentrations and so on.
• Solutions are homogeneous mixtures of two or more than two components. By homogenous mixture we mean that its composition and properties are uniform throughout the mixture. Generally, the component that is present in the largest quantity is known as solvent.
• Such a solution in which no more solute can be dissolved at the same temperature and pressure is called a saturated solution. An unsaturated solution is one in which more solute can be dissolved at the same temperature.
• Pressure does not have any significant effect on solubility of solids in liquids. It is so because solids and liquids are highly incompressible and practically remain unaffected by changes in pressure.
• Many gases dissolve in water. Oxygen dissolves only to a small extent in water. It is this dissolved oxygen which sustains all aquatic life. On the other hand, hydrogen chloride gas (HCl) is highly soluble in water. Solubility of gases in liquids is greatly affected by pressure and temperature. The solubility of gases increase with increase of pressure.
• Henry was the first to give a quantitative relation between pressure and solubility of a gas in a solvent which is known as Henry's law. The law states that at a constant temperature, the solubility of a gas in a liquid is directly proportional to the pressure of the gas.
• Increase with increase of temperature indicating that the solubility of gases increases with decrease of temperature. It is due to this reason that aquatic species are more comfortable in cold waters rather than in warm waters.
• Henry's law finds several applications in industry and explains some biological phenomena. Notable among these are:
• To increase the solubility of \[C{{O}_{2}}\] in soft drinks and soda water, the bottle is sealed under high pressure.
• Scuba divers must cope with high concentrations of dissolved gases while breathing air at high pressure underwater. Increased pressure increases the solubility of atmospheric gases in blood. When the divers come towards surface, the pressure gradually decreases. This releases the dissolved gases and leads to the formation of bubbles of nitrogen in the blood. This blocks capillaries and creates a medical condition known as bends, which are painful and dangerous to life. To avoid bends, more...

 Hydrogen   1.           Position of Hydrogen in the Periodic Table  

• Hydrogen has the simplest atomic structure among all the elements around us in Nature. In atomic form it consists of only one proton and one electron. However, in elemental form it exists as a diatomic (\[{{H}_{2}}\]) molecule and is called dihydrogen. It forms more compounds than any other element. In the global concern related to energy can be overcome to a great extent by the use of hydrogen as a source of energy.
• Hydrogen has electronic configuration \[1{{s}^{1}}\]. On one hand, its electronic configuration is similar to the outer electronic configuration (\[n{{s}^{1}}\]) of alkali metals, which belong to the first group of the periodic table. On the other hand, like halogens (with \[n{{s}^{2}}n{{p}^{5}}\] configuration belonging to the seventeenth group of the periodic table), it is short by one electron to the corresponding noble gas configuration, helium (\[1{{s}^{2}}\]).
• Hydrogen, therefore, has resemblance to alkali metals, which lose one electron to form unipositive ions, as well as with halogens, which gain one electron to form uninegative ion. Like alkali metals, hydrogen forms oxides, halides and sulphides. However, unlike alkali metals, it has a very high ionization enthalpy and does not possess metallic characteristics under normal conditions. In fact, in terms of ionization enthalpy, hydrogen resembles more with halogens.
• Like halogens, it forms a diatomic molecule, combines with elements to form hydrides and a large number of covalent compounds. However, in terms of reactivity, it is very low as compared to halogens.
• Inspite of the fact that hydrogen, to a certain extent resembles both with alkali metals and halogens, it differs from them as well.
• Dihydrogen is a colourless, odourless, tasteless, combustible gas. It is lighter than air and insoluble in water.
• Hydrogenation of vegetable oils using nickel as catalyst gives edible fats (margarine and vanaspati ghee).

    2.           Dihydrogen (\[{{H}_{2}}\])  

• Dihydrogen is the most abundant element in the universe (70 per cent of the total mass of the universe) and is the principal element in the solar atmosphere.
• The giant planets Jupiter and Saturn consist mostly of hydrogen. However, due to its light nature, it is much less abundant (\[0.15\]per cent by mass) in the earth's atmosphere.
• In the combined form it constitutes \[15.4\]per cent of the earth's crust and the oceans.
• In the combined form besides in water, it occurs in plant and animal tissues, more...

The s - Block Elements   1.           In Periodic Table  

• The s-block elements of the Periodic Table are those in which the last electron enters the outermost s-orbital. As the s-orbital can accommodate only two electrons, two groups (1 & 2) belong to the s-block of the Periodic Table.
• Group 1 of the Periodic Table consists of the elements: lithium, sodium, potassium, rubidium, caesium and francium. They are collectively known as the alkali metals. These are so called because they form hydroxides on reaction with water which are strongly alkaline in nature.
• The elements of Group 2 include beryllium, magnesium, calcium, strontium, barium and radium. These elements with the exception of beryllium are commonly known as the alkaline earth metals. These are so called because their oxides and hydroxides are alkaline in nature and these metal oxides are found in the earth's crust.
• Among the alkali metals sodium and potassium are abundant and lithium, rubidium and caesium have much lower abundances. Francium is highly radioactive.

  2.           Uses of s Block Elements  

• Lithium metal is used to make useful alloys, for example with lead to make "white metal’ bearings for motor engines, with aluminium to make aircraft parts.
• And with magnesium to make armour plates. It is used in thermonuclear reactions. Lithium is also used to make electrochemical cells.
• Sodium is used to make a \[Na/Pb\]alloy needed to make \[PbE{{t}_{4}}\] and \[PbM{{e}_{4}}\]. These organolead compounds were earlier used as anti-knock additives to petrol, but nowadays vehicles use lead-free petrol.
• Liquid sodium metal is used as a coolant in fast breeder nuclear reactors.
• Potassium has a vital role in biological systems. Potassium chloride is used as a fertilizer. Potassium hydroxide is used in the manufacture of soft soap. It is also used as an excellent absorbent of carbon dioxide.
• Caesium is used in devising photoelectric cells.
• Uses of Sodium Carbonate (Washing Soda), \[N{{a}_{2}}C{{O}_{3}}.10{{H}_{2}}O:\]
• It is used in water softening, laundering and cleaning.
• It is used in the manufacture of glass, soap, borax and caustic soda.
• It is used in paper, paints and textile industries.
• It is an important laboratory reagent both in qualitative and quantitative analysis.

  3.           more...

 The p - Block Elements   1.           The Boron Family  

• Boron is a fairly rare element, mainly occurs as orthoboric acid, (\[{{H}_{3}}B{{O}_{3}}\]), borax, \[N{{a}_{2}}{{B}_{4}}{{O}_{7.}}10{{H}_{2}}O\], and kemite, \[N{{a}_{2}}{{B}_{4}}{{O}_{7}}.4{{H}_{2}}O\]. In India borax occurs in Puga Valley (Ladakh) and Sambhar Lake (Rajasthan).
• Aluminium is the most abundant metal and the third most abundant element in the earth's crust (\[8.3\]per cent by mass) after oxygen (\[45.5\]per cent) and Si (\[27.7\]per cent). Bauxite, and cryolite, are the important minerals of aluminium. In India it is found as mica in Madhya Pradesh, Kamataka, Orissa and Jammu.
• Gallium, indium and thallium are less abundant elements in nature.
• Boron is non-metallic in nature. It is extremely hard and black coloured solid. It exists in many allotropic forms. Due to very strong crystalline lattice, boron has unusually high melting point. Rest of the members are soft metals with low melting point and high electrical conductivity.
• It is worthwhile to note that gallium with unusually low melting point (\[303\]K), could exist in liquid state during summer. Its high boiling point (\[2676\]K) makes it a useful material for measuring high temperatures. Density of the elements increases down the group from boron to thallium.
• Boron is unreactive in crystalline form. Aluminium forms a very thin oxide layer on the surface which protects the metal from further attack.
• White fumes appear around the bottle of anhydrous aluminium chloride. Reason is that Anhydrous aluminium chloride is partially hydrolysed with atmospheric moisture to liberate \[HC1\]gas. Moist \[HC1\] appears white in colour.
• Borax is the most important compound of boron. It is a white crystalline solid. On heating, borax first loses water molecules and swells up. On further heating it turns into a transparent liquid, which solidifies into glass like material known as borax bead.
• The metaborates of many transition metals have characteristic colours and, therefore, borax bead test can be used to identify them in the laboratory. For example, when borax is heated in a Bunsen burner flame with \[CoO\]on a loop of platinum wire, a blue coloured \[Co{{(B{{O}_{2}})}_{2}}\] bead is formed.
• Boric acid is considered as a weak acid because it is not able to release proton \[({{H}^{+}})\] ions on its own. It receives \[O{{H}^{-}}\]ions from water molecule to complete its octet and in turn releases \[{{H}^{+}}\] ions.

    2.           Uses of Boron and Aluminium and their Compounds  

• Boron being extremely hard refractory solid of high melting point, low density and very more...

 Surface Chemistry   1.           Adsorption and Absorption  

• In adsorption, the substance is concentrated only at the surface and does not penetrate through the surface to the bulk of the adsorbent, while in absorption, the substance is uniformly distributed throughout the bulk of the solid. For example, when a chalk stick is dipped in ink, the surface retains the colour of the ink due to adsorption of coloured molecules while the solvent of the ink goes deeper into the stick due to absorption. On breaking the chalk stick, it is found to be white from inside.
• A distinction can be made between absorption and adsorption by taking an example of water vapour. Water vapours are absorbed by anhydrous calcium chloride but adsorbed by silica gel. In other words, in adsorption the concentration of the adsorbate increases only at the surface of the adsorbent, while in absorption the concentration is uniform throughout the bulk of the solid,

 

• Applications of Adsorption: The phenomenon of adsorption finds a number of application. Important ones are listed here :
• Production of high vacuum: The remaining traces of air can be adsorbed by charcoal from a vessel evacuated by a vacuum pump to give a very high vacuum.
• Gas masks: Gas mask (a device which consists of activated charcoal or mixture of adsorbents) is usually used for breathing in coal mines to adsorb poisonous gases.
• Control of humidity: Silica and aluminium gels are used as adsorbents for removing moisture and controlling humidity.
• Removal of colouring matter from solutions: Animal charcoal removes colours of solutions by adsorbing coloured impurities.
• Heterogeneous catalysis: Adsorption of reactants on the solid surface of the catalysts increases the rate of reaction. There are many gaseous reactions of industrial importance involving solid catalysts. Manufacture of ammonia using iron as a catalyst, manufacture of \[{{H}_{2}}S{{O}_{4}}\] by contact process and use of finely divided nickel in the hydrogenation of oils are excellent examples of heterogeneous catalysis.
• Separation of inert gases: Due to the difference in degree of adsorption of gases by charcoal, a mixture of noble gases can be separated by adsorption on coconut charcoal at different temperatures.
• In curing diseases: A number of drugs are used to kill germs by getting adsorbed on them.
• Froth floatation process: A low grade sulphide ore is concentrated by separating it from silica and other earthy matter by this method using pine oil and frothing agent.
• Adsorption indicators: Surfaces of certain precipitates such as silver halides have the property of adsorbing some dyes like eosin, fluorescein, etc. and thereby producing a characteristic colour at the end point.
• Chromatographic more...

 Miscellaneous: Chemistry   1.           Corrosion  

• Corrosion slowly coats the surfaces of metallic objects with oxides or other salts of the metal. The rusting of iron, tarnishing of silver, development of green coating on copper and bronze are some of the examples of corrosion. It causes enormous damage to buildings, bridges, ships and to all objects made of metals especially that of iron. We lose crores of rupees every year on account of corrosion.
• In corrosion, a metal is oxidised by loss of electrons to oxygen and formation of oxides. Corrosion of iron (commonly known as rusting) occurs in presence of water and air. At a particular spot of an object made of iron, oxidation takes place and that spot behaves as anode.
• The ferrous ions are further oxidised by atmospheric oxygen to ferric ions which come out as rust in the form of hydrated ferric oxide and with further production of hydrogen ions.
• Prevention of corrosion is of prime importance. It not only saves money but also helps in preventing accidents such as a bridge collapse or failure of a key component due to corrosion. One of the simplest methods of preventing corrosion is to prevent the surface of the metallic object to come in contact with atmosphere. This can be done by covering the surface with paint or by some chemicals (e.g., bisphenol). Another simple method is to cover the surface by other metals (Sn, Zn, etc.) that are inert or react to save the object. An electrochemical method is to provide a sacrificial electrode of another metal (like Mg, Zn, etc.) which corrodes itself but saves the object.

  2.           Rusting of Iron  

• Rusting of Iron is one change that affects iron articles and slowly destroys them. For rusting, the presence of both oxygen and water (or water vapour) is essential.
• In fact, if the content of moisture in air is high, which means if it is more humid, rusting becomes faster.
• People who lives near, the coast always complaining about iron articles rusting so fast.
• So, how do we prevent rusting? Prevent iron articles from coming in contact with oxygen, or water, or both. One simple way is to apply a coat of paint or grease.
• Another way is to deposit a layer of a metal like chromium or zinc on iron. This process of depositing a layer of zinc on iron is called galvanisation. The iron pipes we use more...

 THE HARAPPAN CULTURE: BRONZE AGE CIVILIZATION   THE INDUS or the Harappan culture is older than the chalcolithic cultures which have been treated earlier, but it is far more developed than these cultures. It arose in the north-western part of the Indian subcontinent. It is called Harappan because this civilization was discovered first in 1921 at the modern site of Harappa situated in the province of West Punjab in Pakistan. It extended from Jammu in the north to the Naramada estuary in the south, and from the Makran coast of Baluchistan in the west to Meerut in the north-east. The area formed a triangle and accounted for about 1,299,600 square kilometers.        Nearly 1500 Harappan sites are known so far in the subcontinent. Of these, the two most important cities were Harappa in Punjab and Mohenjo-Daro (literally the mound of the dead) in Sindh, both forming parts of Pakistan. Situated at a distance of 483 kilometers they were linked together by the Indus. A third city lay at Chanhu daro about 130 km south of Mohenjo-Daro in Sindh, and a fourth at Lothal in Gujarat at the head of the Gulf of Cambay. A fifth city lay at Kalibangan, which means black bangles, in northern Rajasthan. A sixth called Banawali is situated in Hissar district in Haryana. It saw two cultural phases, pre-Harappan and Harappan, similar to that of Kalibangan. The Harappan culture is noticeable in its mature and flourishing stage at all these six places. It is also found in its mature phase in the coastal cities of Sutkagendor and Surkotada, each one of which is marked by a citadel. The later Harappan phase is found in Rangpur and Rojdi in the Kathiawar peninsula in Gujarat. In addition to these, Dholavira lying in the Kutch area of Gujarat shows Harappan fortification and all the three phases of the Harappan culture. These phases also appear in Rakhigarhi which is situated on the Ghaggar in Haryana and is much bigger than Dholavira.   Town Planning and Structures The   Harappan   culture   was distinguished by its system of town planning. Harappa and Mohenjo-Daro each had its own citadel in each city lay a lower town containing brick houses, which were inhabited by the common people. The remarkable thing about the arrangement of the houses in the cities is that they followed the grid system. According to it, roads cut across one another almost at right angles, and the city was divided into so many blocks. This is true of almost all Indus settlements.   The most important public place of Mohenjo-Daro seems to be the Great Bath, comprising the tank which is situated in the citadel mound. It is an example of beautiful brickwork. It measures 11.88 x 7.01 meters and 2.43 meters deep. Flights of steps at either end lead to the surface. There are side rooms for changing clothes. The floor of the Batch was made of burnt bricks. It is suggested more...

 THE LATER VEDIC PHASE   EXPANSION IN THE LATER VEDIC PERIOD (C. 1000-500 B.C.) THE HISTORY of the later Vedic period is based mainly on the Vedic texts which were compiled after the age of the Rig Veda. The collections of the Vedic hymns or mantras were known as the Samhitas. For purposes of recitation, the prayers of the Rig Veda were set to tune, and this modified collection was known as the Sama Veda Samhita. In addition to the Sama Veda. In post-Rig Vedic times two other collections were: composed. These were the Yajur Veda Samhita and the Atharva Veda Samhita. The Yajur Veda contains not only hymns but also rituasis which have to accompany their recitation. The Atharva Veda contains charms and spells to ward off evils and diseases. The Vedic Samhitas were followed by the composition of a series of texts known as the Brahmanas. These are full of ritualistic formulae and explain the social and religious meaning of rituals.   All these later Vedic texts were compiled in the upper Gangetic basin in circa 1000-500 B.C. These are called Painted Grey Ware (PGW) sites because they were inhabited by People who used earthen bowls and dishes made of painted grey pottery. They also used iron weapons. With the combined evidence from the later Vedic texts and PGW iron- phase archaeology we can an idea of the life of the people in the first half of the first millennium B.C. in western Uttar Pradesh and adjoining areas of Punjab, Haryana and Rajasthan.   The texts show that the Aryans expanded from Punjab over the whole of western Uttar Pradesh covered by the Ganga-Yamuna doab. The Bharatas and Purus, the two major tribes, combined and thus formed the Rum people. In the beginning they lived between the Sarasvati and the Drishadvati just on the fringe of the doab. Soon the Kurus occupied Delhi and the upper portion of the doab, the area called Kurukshetra or the land of the Kurus. Gradually they coalesced with a people called the Panchalas, who occupied the middle portion of the doab. The authority of the Kuru-Panchala people spread over Delhi, and the upper and middle portion of the doab. The authority of the Kuru-Panchala people spread over Delhi, and the upper and middle parts of the doab. They set up their capital at Hastinapur situated in the district of Meerut. The history of the Kuru tribe is important for the battle of Bharata, which is the main theme of the great epic called the Mahabharata. This war is supposed to have been fought around 950 B.C. between, the Kauravas and the Pandavas, although both of them belonged to the Kuru clan. As a result practically the whole of the kuru clan was wiped out.   Towards the end of the later Vedic period, around 600 B.C. the Vedic people spread from the board further east of Koshala in eastern Uttar Pradesh and videha in more...

  TERRITORIAL STATES AND THE FIRST MAGADHAN EMPIRE   The Mahajanapadas In the age of the Buddha we find 16 large states called Mahajanapadas, They were mostly Bituated north of the Vindhyas and extended from the north-west frontier to Bihar. Of these Magadha, Koshala, Vatsa and Avanti seem to have been considerably powerful. Beginning from the east we hear of the kingdom of Anga which covered the modern districts of Monghyr and Bhagalpur. It had its capital at Champa, Eventually the kingdom, of Anga was swallowed by its powerful neighbor Magadha.   Magadha embraced the former districts of patna, Gaya and parts of Shahbad, and grew to be the leading state of the time. North of the Ganga in the division of Tirhut was the state of the Vajjis which included eight clans. But the most powerful were the Lichchhavis with their capital at Vaishali which is identical with the village of Basarh in the district of Vaishali. The Pumas push the antiquity of Vaishali to a much earlier period, but archaeologically Basarh was not settled until the sixth century B.C. Further west we find the kingdom of Kashi with its capital at Varanasi. In the beginning Kashi appears to be the most powerful of the states, but eventually it had to submit to the power of Koshala.   Koshala embraced the area occupied by eastern Uttar Pradesh and had its capital at Shravasti, which is identical with Sahet- Mahet on the borders of Gonda and Bahraich districts in Uttar Pradesh. But we see the beginnings of a mud fort. Koshala contained an important city called Ayodhya, which is associated with the story in the Ramayana. Koshala also included the tribal republican territory of the Shaky as of Kapilvastu. The capital of Kapilavastu has been identified with Piprahwa in Basti district. Lumbini, which lies at a distance of 15 km from Piprahwa in Nepal served as another capital of the Shakyas. In an Ashokan inscription it is called the birthplace of Gautama Buddha and it was here that he was brought up.   In the neighborhood of Koshala lay the republican clan of the Mallas, One of the capitals of the Mallas lay at Kushinara where Gautama Buddha passed away. Kushinara is identical with Kasia in Deoria district. Further west lay the kingdom of the Vatsas, along the bank of the Yamuna, with its capital at Kaushambi near Allahabad. The Vatsas were a Kuru clan who had shifted from Hastinapur and settled down at Kaushambi. Kaushambi was chosen because of its location near, the confluence of the Ganga and the Yamuna. We also hear of the older states of the Kurus and the Panchalas which were situated in western Uttar Pradesh, but they no longer enjoyed the political importance which they had attained in the later Vedic period.   In central Malwa and the adjoining par of Madhya Pradesh lay the state of the Avanti’s. It was divided more...