Category Science & Technology

            An acid is a chemical, which when dissolved in water, gives a solution containing hydrogen ions. Acids turn blue litmus red, they react with certain metals to release hydrogen, they react with bases to form salts and they promote certain chemical reactions.

            All acids taste sour. Fruits such as lemons taste sour because they contain citric acid. Vinegar is sour because it contains acetic acid.

            There are two main chemical groups of acids. They are organic and inorganic acids. Organic acids contain carbon while inorganic acids don’t. Some examples of inorganic acids are hydrochloric acid, nitric acid and sulphuric acid. They are also called mineral acids and they are very strong. Formic acid, acetic acid, etc are organic acids. They are weaker acids.

            Most of the organic acids are harmless. But inorganic acids can be dangerous as they can burn the skin. How do acids burn the body?

            Inorganic acids have a strong tendency to absorb water and release a lot of heat in the process. Since most of the living cells contain water, strong acids like hydrochloric, sulphuric and nitric acid react with them and kill the cells, causing severe burns.

            Acids are also essential for the body. Our stomachs contain hydrochloric acid to digest food. The stomach lining protects us from the acid, if the lining breaks; the acid can burn and cause an ulcer. Amino acids are essential for all kinds of life. Eight special amino acids are needed to stay alive.

            Acids also have tremendous industrial importance. Millions of tons of sulphuric acid is made every year and used for many industrial purposes. It dissolves rust and scale deposited on iron. Acids are also used in making fertilizers, pigments, dyes, plastics and synthetics. Aquaregia, which is a mixture of nitric and hydrochloric acid, is used to dissolve gold and platinum.

            Certain precautions are taken by people handling acids. They wear special clothes to protect their bodies’ from burns. Acids must always be poured slowly into water and never the other way round. If you are burnt by an acid, you should wash your skin with a lot of water, followed by a weak ammonia solution. If your eyes are affected, wash them immediately with water and then with sodium bicarbonate solution, which neutralizes any acid left.

 

        Dyes are colour substances which impart their colour to the fabrics on which they are applied and for which they have a chemical affinity.

          Until the middle of the last century, the only dyes available were natural products obtained mostly from plants and flowers. Their range was limited. These natural dyes included: woad, a blue dye obtained from the plant woad; indigo, another blue dye from a plant. Some other dyes such as madder (red) safflower and turmeric (yellow) were extracted from certain kinds of sea-snails.

          The most important breakthrough in this field was made in 1856 with the discovery of the first synthetic dye by William Henry Perkin. This was mauveine, a bluish-purple dye discovered accidentally by William Perkin during experiments aimed at synthesizing the drug quinine. After this discovery, efforts were made to develop dyes from coal tar. As a result of these efforts, several thousand dyes were synthesized subsequently.

          These synthetic dyes were satisfactory when used with animal fibres such as wool, but they were easily washed off from vegetable fibres like cotton. This difficulty was overcome by treating the fibres with metal salts or with solutions of these salts in tannic acid before dyeing.

          After these dyes a large number of azo dyes were developed. Azo dyes are two component dyes used for cellulose fibres. The material is first treated with one component, and then put in the solution of the other component. The two components react to produce a dye within the fibres themselves. These dyes are highly resistant to washing.

          Another group of very stable dyes used for cellulose fibres is known as Vat dyes. These dyes, which include synthetic indigo used for dyeing blue denim, are mixed with chemicals to make them soluble for the dyeing process. After the material has been dyed, it is treated with other chemicals to make it more stable.

          Today we have a large number of synthetic dyes obtained from coal tar or petroleum products which are not only used to colour textiles, but also plastics, paper, leather, fur, oil, rubber, soap, food, cosmetics, ink and metal surfaces. 

Man has been using soap and water as cleaning agents for thousands of years. The first soap was made in the middle east about 5000 years ago. The discovery of soap less detergents is not very old. The first synthetic detergent was not invented until 1916, but since then the manufacture of non – soap detergents became a major development of the petrochemical industry. New methods of fabric cleaning came into use, such as dry cleaning.

Dry cleaning is a method of cleaning fabrics with chemical solvents instead of soap and water. Many of these solvents are derivatives of crude oil. Petrol is the most important of them. Benzene is also used in dry cleaning. Their fumes can be dangerous if inhaled and they catch fire easily. Some safer synthetic chemicals such as polychloroalkanes and alkanes have also been developed. The most common dry cleaning chemicals are carbon tetrachloride and trichloro ethylene.

In a dry cleaning establishment, clothes are usually treated first for stains. Then they are placed in the dry-cleaning machine with the cleaning fluid or solvent and tumbled slowly for up to half an hour. After a rinse in clean fluid, the clothes are spun around rapidly to extract the liquid, and are finally fluffed in hot air. Any stains remaining are removed by hand and clothes and then steam pressed.

Dry cleaning has several advantages over ordinary soap cleaning. Cleaning fluids can dissolve stains (especially oil and grease) which soap and detergents cannot remove. The process is most useful for delicate or expensive silken and woollen fabrics because it does not have any undesirable effect on them. For instance, the colours do not fade, as they might in water. 

          Quartz is a hard, glossy mineral made of silicon and oxygen. It is found in most kinds of rocks in colourless, often transparent form. There are also coloured varieties including semi-precious stones such as amethyst and citrine. Pure quartz is called rock crystal also. In appearance it looks like glass. It has six sided crystalline structure. It ranks 7 on the Mohs’ scale of hardness and is resistant to chemical or mechanical breakdown.

          Quartz is extremely hard and will scratch glass. It melts at a very high temperature. It can be made into tubes, sheets or blocks. It can also be blown into various shapes by using oxy-hydrogen flame.

          Quartz has great economic importance. Sandstone, composed mainly of quartz, is an important building stone. Large amount of quartz sand is used in the manufacture of glass and porcelain and in metal casting for foundry moulds. Quartz is used as an abrasive in sandpaper and grindstones. It is used to make prisms and lenses which can transmit ultra-violet light. Tubing and various vessels of fused quartz have important laboratory application. It is also used in ornamental work and industry where its reaction to electricity makes it valuable in electronic instruments. Quartz fibres are used in extremely sensitive weighing devices.

          Quartz is a piezoelectric material, i.e. when pressure is applied across the two surfaces of a quartz crystal, an electric voltage develops across the crystal and when voltage is applied across the two faces of the crystal, and it expands, or contracts. Due to this property, it can help to change electric signals into sound waves and vice versa. The piezoelectric property of quartz plays an important role in radios, television and radar. Quartz oscillators are used in Quartz crystal watches to give accurate time.

          Natural quartz crystals of commercial grade are obtained from Brazil. Quartz can also be made synthetically.