Category Chemistry

What is Plastic?

            Plastics do not occur naturally but are manufactured. The word ‘plastic’ has originated from the Greek word ‘Plastikos’ which means ‘to mould’. It is made from simple organic chemicals. It has many varieties and colours.

            Plastic was invented by Alexander Parkes of England in 1862. In those days it was called ‘Parkesine’ after him. Parkesine was the first plastic ever produced.

            Many plastics have ‘poly’ in their names for example, polythene. Poly comes from a Greek word meaning ‘many’. Polythene means ‘many molecules of ethene joined together’.

                   The manufacturing of plastic on a commercial scale was started for the first time by Leo Hendirk Backeland. He made it from phenol and formaldehyde. Subsequently, new techniques were developed for the production of plastics. Today, scientists have discovered many raw materials which are used in the making of various kinds of plastic products. Most plastics are made from chemicals found in oil, although a few come from wood, coal and natural gas. Common types include polythene, polystyrene, PVC and nylon.

                  Today, plastic has become an integral part of our life. Its uses are endless. Transparent plastics are used for making lenses and windows of aeroplanes. Polythene bags, a plastic product, are used in almost all walks of life. Articles of domestic use like buckets, cups, brushes, combs, baskets, cabinets for radios, transistors etc. are also made of plastics. Toys and sports goods made from plastic have flooded the markets everywhere. The yarn for making Terylene cloth is, in fact, made from plastic. Today scientists have even succeeded in developing heat insulating plastics. Foam cushions, seats in trains, cars and aeroplanes – all are made from plastics. Now, plastics are used as surgical aids also. There is hardly any field of life in which plastics are not used. 

What is dry ice?

Ice, which we generally see around us, is made by freezing the water. Water turns into ice when it is cooled to 0°C. There is another kind of ice which is known as dry ice.

Dry ice is solid carbon-dioxide. It is formed when carbon-dioxide turns directly from a gas into a solid at a temperature of about – 80°C. It is so cold that if held in hand it causes frost bite. It is usually prepared by cooling carbon-dioxide under high pressure. It looks rather like snow but can be made into blocks by compressing the flakes. Dry ice is very heavy.

Dry ice is very important for cooling or refrigerating foods such as ice creams and meat and medicines. It is also used to stimulate fog and steam effects in television or stage plays because it rapidly turns back to gas at ordinary temperature without becoming liquid.

 

How do we get Wool from Sheep?

             Warm clothes that we wear during the winter are mostly made of wool which comes from sheep. Wool is also obtained from goats and other animals like llama and alpaca. Mostly it is the wool from sheep that we use for our winter dresses. Wool is basically fine soft hair that forms the coats of these above mentioned animals. Hair grows on the body of sheep, as they grow on our heads. Sheep and similar other animals have fine thick wool hair which are called fleece. The fleece or hair of a sheep insulates it from the cold in winter. In other words, wool is animal fibre forming the protective covering or fleece of sheep. Do you know how this wool comes to you from sheep? Wool is mainly obtained by shearing fleece from living animals and sometimes from slaughtered sheep also.

              When the fleece is sheared, it is rolled up in bundles sorted out into different qualities or grades, cleaned; stains of various types, dried, entangled fibres are disentangled, twisted and spun in soft, loose irregular thread or yarn. Such strands used together are called 2-ply, 3-ply etc., according to the coarseness or fineness of fabric desired. Wool may be dyed at the various stages of the manufacturing process. Wool fibre is warmer but coarser than cotton, linen, silk and rayon.

 

Continue reading “How do we get Wool from Sheep?”

How is copper useful to us?

              Copper is a reddish orange metal that has been used for more than 5000 years. After gold it was the first metal to be discovered by man. Native copper is found in small quantities in solid or granular form. Most of it occurs in the combined state as sulphides, carbonates, silicates and oxides. Copper pyrite is its most important ore. About 50% of world’s supply of copper comes from copper pyrite.

                     History reveals that copper was used by man as early as the Stone Age. By 4000 B.C. mining of copper had begun, by 6000 B.C. man had started using instruments, weapons and ornaments of copper. Later, man came to know that bronze, an alloy of Cu, Zn and Sn is harder than Cu. He then used bronze for making utensils, weapons and ornaments. Other alloys of copper like brass are also used for the same purposes. Copper also makes an alloy with aluminium which is called aluminium bronze. As time passed copper came to be one of the most important metals in the world, used extensively in electrical and other industries for making wires, dynamo, coils, motor coils, for minting purposes, to make coins, in engineering industry and so on. Copper is used all over the world for making electric wires because of its softness and tenacity. It is a very good conductor of electricity and heat. Much of the world’s copper comes from Canada, USA, Chile, Zambia and Russia. 

What is helium?

Most of the gases can be prepared in the laboratory but there are some which are found in nature only. Helium is one such gas.

                It is an inert gas. It is odourless and tasteless. Helium has some special characteristics due to which it has proved very useful for us. It is second lightest gas next to hydrogen but it has a speciality that, unlike hydrogen, it is non inflammable.

               This gas was discovered in 1868 independently by English scientists Sir Joseph Norman Lockyer and French Chemist, Pierre Janssen. While studying the solar spectrum to find the elements present in the sun, they came across some lines which were not observed earlier. These lines suggested the presence of a new element in the sun. The element was named as Helium after the Greek word ‘helios’ meaning ‘the sun’. Thereafter, scientists made efforts to know if helium was present in the earth’s atmosphere. They detected very small quantities of helium in the atmosphere. Atmospheric air contains only one part in 1, 86,000 parts, i.e., 0.0005239 percent.

               On account of its lightness and non-inflammability, it is used in weather balloons. Helium is also used to ease the breathing difficulties of asthmatic patients. Deep sea divers are given a mixture of oxygen and helium for breathing so that after coming back, they do not suffer with bends. Helium is also used to weld aluminium. A mixture of helium and neon is used to produce laser beams. Helium can be liquefied at – 268.9 degree centigrade. Liquid helium is used in low temperature work.

               There are some places in America like Texas, New Mexico, and Kansas etc. where the amount of helium present in the atmosphere goes upto 8%. It is also present in atmosphere in Canada, Africa and the Sahara desert. America is the world’s richest source of this gas and is therefore the biggest seller of helium to other countries. In earlier times this gas was very costly, but now it has become quite cheaper.

How is oxygen useful to us?

                 Without oxygen there would have been no life on this earth. Without it no living being – trees, plants or animals can survive. Hence it will not be a misnomer to call it a life-giver. Do you know what is it and why is it absolutely essential for us?

                Oxygen is a gaseous element. This was discovered by two scientists independently. Carl Scheele, a Swedish chemist, discovered oxygen in 1772 and Joseph Priestley, discovered it in 1774 in England. It is a colourless, tasteless and odourless gas. In the atmosphere the air contains 21% oxygen, 78% nitrogen and rest one percent other gases. In the earth’s crust, it is found in the form of oxides of metals, the proportion being up to 50%. At – 182.9°C under right pressure it can be liquefied. In the liquid state its colour becomes light blue. At – 218.4°C, it can be converted into solid state.

               In the laboratory, this is obtained by heating the mixture of potassium chlorate and manganese dioxide. From the atmosphere, it is obtained by the fractional distillation of air. The air is compressed to two hundred times the normal atmospheric pressure and passed through a narrow hole into a chamber. As the pressure is suddenly dropped, the air is liquefied and collected in the chamber. The nitrogen gas is separated from this by a special method and oxygen is obtained in the liquid state.

              All living beings need oxygen for breathing. Plants also ‘breathe’ oxygen. They absorb oxygen during the night. During the day they give off oxygen by photosynthesis.

              By burning oxygen gas along with the acetylene gas, a high temperature flame is produced. This flame is used for welding and cutting metals. Liquid oxygen is also used as a fuel in space vehicles.

 

Continue reading “How is oxygen useful to us?”