14. Substances in Common Use

Crystalline washing soda is Na₂CO₃·10H₂O. On keeping in air it loses nine of these molecules and becomes a white powder, Na₂CO₃·H₂O.

The property of spontaneously emitting invisible, highly penetrating and high-energy radiation, shown by elements of high atomic number such as uranium, thorium and radium, is called radioactivity. The radiation comes from the unstable nucleus and is of three types — alpha, beta and gamma rays. Substances with this property are called radioactive substances.

A nucleus is said to be unstable when it cannot hold its protons and neutrons together permanently. This happens in heavy elements with a high atomic number (generally 82 to 92), whose nuclei have too many protons and neutrons, or an unsuitable proportion of neutrons to protons. Such a nucleus breaks down spontaneously and emits alpha, beta or gamma radiation until it becomes stable.

• Artificial colours in pickles, jam and sauce contain small amounts of lead and mercury, which harm people who eat these products regularly.
• Excessive consumption of foods with added colours can cause ADHD (Attention Deficit Hyperactivity Disorder) in children.
• They may also cause allergies, skin rashes and stomach disorders.

• Radiography: gamma rays from cobalt-60 or iridium-192 in a radiography camera detect internal cracks and voids in cast-iron articles and welded joints.
• Measuring thickness, density and level: the radiation passing through aluminium, plastic or iron sheets during manufacture shows whether the required thickness is maintained; material inside packing can also be examined.
• Luminescent paint: radium, promethium and tritium with a phosphor make clock hands and other objects visible in the dark.
• Lamps and portable X-ray units: krypton-85 is used in HID lamps and promethium-147 as a source of beta rays in portable X-ray units.
• Ceramics: uranium oxide was earlier used in luminous colours for decorating ceramic articles.

• The atmosphere and chemical substances have no effect on Teflon.
• Neither water nor oil sticks to Teflon-coated articles.
• High temperatures do not affect it, as its melting point is 327°C.
• Teflon-coated articles are easy to clean.
• It is a poor conductor of electricity.

I will use natural colours made from plants: red and pink from beetroot, orange and yellow from the flowers of flame of the forest (palash) and gulmohar, and marigold, green from spinach or henna leaves, and yellow from turmeric.

Why: artificial colours contain harmful chemicals. The red colour, for example, contains a high proportion of mercury, which can cause blindness, skin cancer, asthma, itching and permanent blocking of sweat pores. Natural colours are safe for the skin, eyes and hair, are easily washed off, and do not pollute water or soil.

• Food does not stick to Teflon-coated (non-stick) utensils, so cooking needs very little oil, which is good for health.
• Coated utensils and articles are very easy to clean.
• Teflon is not affected by chemicals, water, air or high temperature (up to its melting point of 327°C), so it protects the article and lasts long.
• Being a poor conductor, it is used to insulate wires and parts in electronic instruments, and it protects vehicle parts from heat and rain.

Bleaching powder (calcium oxychloride) slowly decomposes by reacting with the carbon dioxide in the air, releasing chlorine gas:

Because chlorine is continuously released in small amounts, bleaching powder always smells of chlorine.

Water from wells and bore-wells is hard because it contains dissolved chlorides and sulphates of calcium and magnesium. When washing soda (Na₂CO₃) is added, it reacts with these salts to form insoluble calcium and magnesium carbonates, which settle down:

The calcium and magnesium ions are thus removed from the water, so it becomes soft and forms lather easily with soap.

Soap is the sodium or potassium salt of fatty acids. Hard water contains calcium and magnesium salts. When soap is mixed with hard water, the calcium and magnesium ions react with it to form calcium and magnesium salts of fatty acids. These are insoluble in water, so they separate out as a white precipitate (scum), and lather does not form.

In powder coating, the powder is sprayed by electrostatic spray deposition. The powder particles are given an electric charge, while the metal object is earthed. The charged particles are attracted to the metal surface and stick to it uniformly, even at corners and edges, so they do not fall off before the object is heated in the oven. Particles carrying the same charge also repel one another, so they spread evenly. As a result, a smooth, uniform layer is formed with very little wastage of powder.

In anodising, the aluminium article is dipped in dilute acid in an electrolytic cell and electric current is passed. Oxygen gas is released at the anode. Since the aluminium article is the anode, this oxygen reacts with its surface and forms a layer of hydrated aluminium oxide of the desired thickness. This layer protects the article from corrosion and can be made attractive by adding colour. If the article were the cathode, only hydrogen would be released on it and no oxide layer would form.

A radioactive substance gives out three types of radiation with different charges:

• Alpha rays are positively charged (He⁺⁺) and heavy, so they deviate slightly towards the negatively charged plate.
• Beta rays are negatively charged electrons and very light, so they deviate substantially towards the positively charged plate.
• Gamma rays are electromagnetic radiation with no charge, so they pass straight without deviation.

The electric field separates the three types into three paths, so they strike the photographic plate at three different places.

When a space shuttle re-enters the earth’s atmosphere at very high speed, friction with the air heats its outer surface to extremely high temperatures. Advanced ceramics can withstand very high temperatures without decomposing or melting, and they are poor conductors of heat. Special ceramic tiles are therefore fixed on the outer layer so that the heat does not reach the inside, protecting the shuttle and the astronauts.

Artificial food colours are synthetic colouring substances added to foods to make them look attractive. They come as powders, gels and pastes, and are used in ice cream, ice candies, sauces, fruit juices, cold drinks, pickles, jams and jellies, sweets, and sometimes even in packaged meat, chilli powder and turmeric.

Substances used: synthetic dyes such as tartrazine (yellow) and sunset yellow, which are prepared from petroleum products. Some colours contain traces of heavy metals such as lead and mercury.

Harmful effects:

• The lead and mercury in colours added to pickles, jam and sauce harm those who consume these products regularly.
• Excessive consumption of coloured foods can cause ADHD (Attention Deficit Hyperactivity Disorder) in children.
• They may cause allergies, rashes and stomach disorders.

Natural food colours made from seeds, beetroot, flowers and fruit concentrates are safer and should be preferred.

The water molecules that are included in a definite proportion in the crystal structure of some ionic compounds are called water of crystallization. It is shown in the formula, as in CuSO₄·5H₂O. On heating, this water is lost and the crystal shape and colour are lost.

1. Electrolysis of a dilute aqueous solution of salt: when a little salt is dissolved in water and electric current is passed, water gets decomposed — hydrogen gas is released at the cathode and oxygen gas at the anode, in the volume ratio 2 : 1. The salt only makes the water a good conductor.
2. Electrolysis of saturated brine: when current is passed through a saturated solution of sodium chloride, hydrogen gas is released at the cathode and chlorine gas at the anode, and sodium hydroxide is formed in the cell. This method is used to manufacture chlorine and NaOH.
   2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
3. Electrolysis of fused salt: when salt is heated to about 800°C it melts (the fused state). On electrolysis of fused salt, chlorine gas is released at the anode and liquid sodium metal at the cathode. This method is used to obtain sodium metal.
   2NaCl (fused) → 2Na + Cl₂

• Forms a thick protective oxide layer on aluminium articles, which prevents corrosion.
• Used for cooking utensils such as griddles and pressure cookers; the layer makes them hard-wearing and keeps food from reacting with the metal.
• Colour can be added during anodizing, so it is used to give an attractive finish to aluminium window frames, doors and other articles.

• Gives iron articles a layer harder than paint, which prevents rusting.
• The coating is highly durable, hard and attractive, so it is used on furniture, cupboards, grills, vehicle parts and appliances.
• It can also be done on plastic and MDF board articles.

• Industry: radiography for detecting cracks in metal; measuring thickness of sheets; luminescent paints.
• Agriculture: improving seeds by changing genes; preserving food with cobalt-60; preventing sprouting of onions and potatoes; strontium-90 as a tracer in crop research.
• Medicine: phosphorus-32 for polycythemia; strontium-89, samarium-153 and radium-223 for bone cancer; radioactive iodine for hyperthyroidism; arsenic-74 to detect small tumours.
• Research: in scientific research, and in nuclear power generation.

• Pots, roofing tiles (Mangalore tiles), bricks, pottery, terracotta articles, porcelain crockery and bone china.
• Porcelain vessels such as crucibles and evaporating dishes in laboratories.
• As electrical insulators in electrical instruments.
• For lining the inside of kilns, on the outer surfaces of ships, in jet engine blades and on the outer layer of space shuttles.
• Some ceramics are used as superconductors.

• Dyeing hair can cause hair fall, damage to hair texture, burning of the skin and harm to the eyes.
• Lipstick contains the dye carmine, which can cause stomach disorders.
• Artificial colours such as those used on Rang Panchami contain harmful chemicals like mercury, which can cause blindness, skin cancer, asthma, itching and blocking of sweat pores.
• Waste dyes from factories pollute water and soil.

• Traces of lead and mercury in them harm those who consume coloured foods regularly.
• Excessive consumption can cause ADHD in children.
• They may cause allergies and stomach problems.

• Radiation affects the central nervous system.
• It damages DNA and causes hereditary defects passed on to the next generations.
• It penetrates the skin and causes diseases like skin cancer and leukaemia.
• Radioactive pollutants from explosions spread through the air and are difficult to control; those released into the sea enter fish and then the human body.
• Strontium-90 enters the body through plants, fruits, cereals and milk and can cause bone cancer and leukaemia.
• Radioactive paint on watch dials can cause cancer. The Chernobyl disaster (1986) showed how serious these effects can be.

The textbook lists these harmful effects:

• Aluminium–zirconium compounds in deodorants may cause headache, asthma, respiratory disorders and heart problems.
• Aluminium chlorohydrate may cause various skin disorders, and possibly skin cancer.
• Antiperspirant deodorants clog the sweat pores and reduce sweating.
• They also contain parabens and alcohol in large proportions, which can irritate the skin.

The picture shows powder coating being done by electrostatic spray deposition (ESD).

• A powder made from a polymer resin, a pigment and some other ingredients — melt-mixed, cooled and ground into a uniform powder — is sprayed from a spray gun on to a polished metal object.
• The powder particles are given an electrostatic charge as they leave the gun, so they are attracted to the metal surface and stick to it as a uniform layer.
• The coated object is then heated in an oven. A chemical reaction in the layer forms long, cross-linked polymer chains.
• The result is a coating that is harder than paint, highly durable and attractive, and prevents the iron object from rusting.

Points to note during the visit:

• Powder coating unit: how the metal surface is cleaned and pre-treated (degreasing, removing rust); how the powder is prepared; how the electrostatic spray gun charges the powder; the temperature and time in the curing oven; which articles are coated.
• Teflon (non-stick) coating unit: how the utensil surface is roughened and cleaned; how the Teflon layers are sprayed; the high-temperature baking; the quality checks.
• Safety measures: masks, gloves, exhaust fans and the handling of waste powder and fumes.

Present the process as a flowchart with photographs, and compare the two methods.