Category Chemistry

What is Carbon Cycle?

               Of all the elements known to man, carbon is one of the most important for him. Diamond, the most valuable gem, is a form of carbon. Graphite is also a form of carbon which forms the lead of lead pencils. Again, coal which is a main source of heat and power in the present age is mostly carbon. The most important fact about carbon is that it is a necessary element for all living things. In fact, scientists believe that wherever carbon has been found in any quantity on the earth, life in all probability existed there. Carbon is the most widely distributed non-metallic element and it is a common constituent of all organic compounds. Do you know what Carbon Cycle is?

               Carbon cycle is the process of constant circulation of carbon between living organisms and the atmosphere. It maintains a balanced percentage of carbondioxide in the air. The main source of carbon for all lives is the carbondioxide gas in the atmosphere. This gas is taken from air and returned to it by all organisms. In this continuous cycle, the limited carbondioxide in the air is being constantly re-used.

               Green plants take in carbondioxide gas from the atmosphere; combine it with water from the soil, to make more complex carbon compounds. Carbondioxide is returned to the air by plants in two ways. Firstly during night they give off carbondioxide. And secondly, when they die and their remains decay, carbondioxide is released into the air.

               Animals, including human beings, get some carbon from the carbondioxide in the air. However, most of their carbon is obtained from plants, vegetables, fruits or cereals. All animals return carbon to the air by breathing out carbondioxide during respiration. Like plants they also give out carbondioxide when they decay after death. Carbondioxide is also released when animals or plants are burnt. Again, when fossil fuels like coal, petroleum or natural gas are burnt, carbondioxide is released into the atmosphere.

               Today, Carbon Cycle is in danger by the increased consumption and burning of fossil fuels and large tracts of tropical forests. As a result, carbondioxide is building-up in the atmosphere breaking the equilibrium and contributing to the global warming as termed by the scientists.

 

What is Ceramics?

               The word ‘ceramics’ has its origin in the Greek word Keramos, which means “potter’s clay”. Today the word refers to all types of pottery, whatever its composition or use. All ceramics are made from various clays, together with materials such as flint, felspar or china clay.

               However, strictly speaking ceramics are compounds of silicon, carbon, oxygen and nitrogen combined with other elements like sodium, potassium, calcium, barium etc. The principal raw material used in the manufacture of ceramics is clay. These clays are formed by decomposing natural rocks which are exposed to the wearing action of air and water. Granite is the rock which provides the bulk of useful clays. It is composed of quartz, mica, felspar etc. These clays are crushed and ground into fine particles. The particles are mixed and moisted with right proportion of water, which makes the particles flexible for shaping. Different methods are used for getting the desired shape.

               After the product has dried, it is heated. This process takes place in a special type of furnace called kiln. Ceramics are heated at temperatures ranging from 650°C to 1650°C. Firing makes the products hard in the desired shape and turns their glaze into a smooth coat. This process also makes the product leak-proof, durable and decorative.

               Clay and shale are used to make building products, such as bricks and drain pipes. Calcium silicates are used in making the cement. Gypsum is used in the manufacture of plaster. Porcelain is used in making bath-tubs, sinks and toilets. Bowls, cups and plates are also made from porcelain. Artificial bone joints and false teeth are made from porcelain.

               Some ceramics such as alumina and porcelain, do not conduct electricity and used as insulators in automobile spark plugs, electric power lines. Some types of capacitors are made from Barium titanate which is a ceramic material. Refractories are another important group of ceramic products used for lining furnaces. They resist heat and chemical action. Alumina, silica and magnesium compounds are used as refractories. Uranium oxide ceramics are used as fuel elements for nuclear reactors. Alumina in the form of ruby is used in the making of lasers, which produce extremely strong light beams.

 

What is the absolute zero?

               It is our common practice to measure our body temperature with the help of a thermometer when we feel feverish. In ordinary thermometers, the lowest temperature is marked as 0°C. Today scientists can produce temperatures well below 0°C. Kelvin William Thomson a British Physicist first pioneered the absolute scale of temperature. The scale which is used to measure low temperatures therefore called ‘Kelvin’ scale or absolute scale of temperature.

               Theoretically the lowest possible temperature which a gas can attain is known as absolute zero. In centigrade scale it is equal to -273.15°C. This is based on the theory that the volume of a gas reduces in correspondence to the fall in temperature. So according to this theory, the gaseous volume would disappear and would loose all its kinetic energy if its temperature was lowered to -273.15°C or absolute zero. The gas molecules would be completely at rest, and it would not possess any heat. In practice, however, all gases change to liquids and then to solids before their temperature reach absolute zero.

               Scientists have never been able to reach absolute zero in their laboratory experiments. The lowest recorded temperature so far was achieved by magnetizing copper nuclei at a low temperature. When the electromagnet was switched off, the copper nuclei became demagnetized; the temperature fall was upto a million part of a degree above absolute zero.

               Materials react strangely when cooled to a temperature near absolute zero. At this temperature, oxygen gas freezes to a bluish white solid, and a rubber ball becomes so brittle that it shatters instead of bouncing. Mercury, normally a liquid, becomes and shines like hard silver. Hydrogen becomes a liquid and begins creeping into the sides of its container. Natural gas is shipped around the world in special containers after being cooled and liquefied at a low temperature.

               The Kelvin scale is used for scientific measurements, e.g. the liquefaction temperature on the Kelvin scale for Hydrogen is 20K and for liquid Helium it is 4.2K.

 

How do ice columns grow inside caves?

               Ice columns appear in many caves or caverns. They are called stalactites and stalagmites. Stalactites are the stony deposits hanging like icicles from roofs of the caves. Stalagmites are similar deposits rising in columns and cones from floors of the caves. Do you know how are they formed?

               Most of the caves occur chiefly in lime stone and chalk formations. Limestone is a fairly soft rock mainly made of calcium carbonate that can be dissolved by a weak acid. The acid that dissolves limestone comes from rain water. Falling drops of rain pick up carbon-dioxide from the air. This carbon dioxide changes the rain water into carbonic acid that dissolves the limestone. The seepage of water down the cave walls and through the roof produces constant dripping and evaporation. Stone icicles formed on the cave roof, slowly grow with the addition of successive layers of calcium carbonate. The word ‘stalactite’ has Greek origin and means ‘drop by drop’. This is why these stone icicles are also known as “dripstone”.

               At the initial stage, the stalactite remains hollow due to faster, carbonate deposit at the outer ring of the water drops. However it slowly turns to solid when the cavity fills up in the process of evaporating the water particles from the mineral substances.

               If the seepage of water is quick the drop might fall on the cave’s floor. It deposits its calcium carbonate there and cones and domes of stone are formed. These are called as stalagmites. They may grow up to join the stalactites above and form single columns. They may even grow as high as to block the entrance of the cave. Each stalactite or stalagmite grows at a different rate, depending on the wetness of the cave, the inside temperature of the cave and the thickness of the limestone bed above it. Some stalactite might grow an inch a year while others would take one hundred years or so to grow that much. When water stops reaching the underground caves, the stalactites stop growing and the cave is considered “dead”. 

How do we get common salt?

               It has been estimated through scientific analysis that the water of the seas contains about four and a half million solid cubic miles of salt. All these salts have reached into the seas from the earth. The rain water and melted snow water dissolve minerals from rocks and flow down through the rivers into the oceans and seas. These are main sources of salt deposits in ocean and sea water. It has been found that on the whole sea water contains about three to three-and-half percent of common salt. But millions of years ago evaporation took place from the water of bays, which were cut off from the sea and became salt lakes.

               Now the question arises, how do we get common salt?

               Common salt in fact is a compound of sodium and chlorine. It also contains several minerals such as iodine. One atom of sodium combines with one atom of chlorine and forms one molecule of sodium chloride.

               Since sea has an abundant quantity of salt, it remains the main source of its supply. To obtain it through artificial means, water is led into wide, shallow basins about 3 feet deep. In the first one the solid impurities like sand, mud and tiny living creatures get settled. Calcium sulphate is also separated from the water in this basin. The water then flows into a succession of basins and evaporates there. In the process, sodium chloride is deposited there. This is collected, dried, refined and purified.

               In cold countries, a different method is used for the extraction of salt. In this, sea water is allowed to freeze, since the ice from frozen sea water does not incorporate the molecules of salt. These accumulate in the unfrozen water under the ice and make it more salty. The floating ice is gradually removed and further frozen, until only a little highly saline water remains. This is collected and evaporated by means of artificial heat, and salt is collected.

               There are many salt deposits in the world. The salt formations of Kansas, Oklahoma, Texas and New Mexico in the U.S.A. cover an area of about 100,000 square miles and are the largest in the world.

               Common salt is basically used for flavouring and preserving food. 

Can fresh water be obtained from the Sea?

               We all know that sea water is salty. It  contains many minerals which make it salty. Salinity of sea water varies a great deal in different parts of the ocean. On an average, there are 35 parts of salt to every 1000 parts of sea water. Now the question is whether it is possible to remove salt from the sea water and make it drinkable.

               There are several methods to make the sea water drinkable. One method is distillation. In this, sea water is boiled and the steam is condensed into water. Water gets vaporized leaving behind the salt. Water so obtained is fresh and good for drinking. For this purpose, nuclear energy or solar energy is used.

               In another method, electrical energy is used. Here, an electrical current is passed through the sea water. The electric current causes positive salt ions to flow in one direction and negative ions in the other. In fact, about 3.5 per cent of sea water consists of dissolved elements. These elements are sodium and chlorine which together form salt. On passing electricity, sodium ions move towards cathode and chlorine ions towards anode. This way, salt is removed from the water and water becomes worth drinking.

               In another method, some special types of membranes are used to purify water. There are thin membranes which let pure water through while blocking the flow of salts. Water filtered with these membranes becomes pure.

                By another method, the sea water is simply frozen. This process extracts salt from the water. After the salt has been separated from the ice, the ice is melted, giving fresh water. But this process is only for limited purposes.

               One of the best methods of obtaining fresh water is called multi-stage flash distillation. In it sea water vaporizes rapidly several times, each time in a higher vacuum and at a lower temperature.

               The world is now faced with an ever-increasing demand for fresh water.

               Scientists in many countries of the world are developing new methods for obtaining fresh water from the sea. In Israel, for example, and other oil-producing countries in Middle East, it has become worthwhile to build big plants to distill fresh water from the sea. However, due to high cost in processing, it is not still considered economically viable as an alternate source of fresh water. The research on the subject is still in experimental stage.