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Encyclopedia about Chemistry


Chemistry and technology

Chemistry can and does find widespread use in technology. Most of the time, the materials employed are used on a day-to-day basis and have been perfected through myriad chemical techniques.

There are over 100 chemical elements known to date, and almost all of them can form multiple compounds. Chemistry is the science of combining these elements in order to form new materials that have an ever wider use.

One of the most far-reaching chemical discoveries was the invention of plastics and other synthetic materials. There are a number of different types of plastics and other synthetic materials, each with its own different properties. Many react as temperature changes. Some, however, are able to withstand changes in temperature.

These find use in situations when a material must be exposed to very high or very low temperature, for example in a heat insulator.

Nature has also been a reliable supplier of the basic materials that we human beings take for granted. In nature, calcium is one of the basic raw materials. From it, lime and limestones in their various forms can be produced, these often being used in the construction industry. Lime is also an ingredient in cements and cement mortar.

With the addition of certain molecules, the colour of numerous materials can be changed. Glass, for example, can be turned brown if a certain concentration of barium carbonate is added to it. It can be turned green if an iron oxide is mixed in.

The colour of foods and foodstuffs is also the domain of chemistry. At the same time, this area of the natural sciences is living proof of the numerous uses and many-sided nature of many of the compounds that make up certain materials.

and who would have thought that our bodies, the coal and other fuels we use to heat our homes, and the bubbles in many of our drinks, are all composed of one and the same element, carbon?

Today’s wide variety of cleaning products were without exception tested in laboratories around the world. This is how we keep things clean: by using chemicals which can quickly and effectively remove stains, and make our world a brighter place to live in.

and what about transportation? Flying, either by airplane or by the precursors of what will one day be spaceships, is the result of long years of chemistry (and physics) research. This brings up a scientific truth: Chemistry, including the chemical industry, is closely related to other natural science branches, such as physics, biology and even mathematics. In many cases, these sciences are so closely related that it is impossible to separate them. That is why, together, they are called the natural sciences.

It is beyond the scope of this document to name all of the things that chemistry has done to improve our world. We can, of course, try to show some of the advances that have been made in the wonderful world of chemistry with the help of a few examples. It is, however, like the view through a narrow keyhole into a large room. It is possible to see a few of the larger features, such as where some of the furniture is placed. But the real content of the room, down to its intricate details - that is impossible to see without much closer examination. So are many of the discoveries made, thanks to chemistry, that we tend to take for granted.

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Sulphur, sulphuric acid and its salts

Sulphur is a member of the sixth main group of the periodic table, Group VIA. It is a yellow solid which is not soluble in water. It is not a metal. In nature, it occurs in two crystalline structures:

monoclinic and hexagonal.

Sulphur burns in air as a blue flame, producing sulphur oxide (SO2). It forms sulphides with a number of metals. It is used in the production of some medicines, rubbers and fungicidal products.

Sulphur is found on Earth in what are called sulphur beds, or deposits. Besides being found in its pure form, sulphur-containing compounds are found in oil, natural gas and in some rock formations which contain carbon and other materials (for example in iron sulphides chemical formula FeS).

Sulphur oxide (SO2)

Sulphur oxide is a colourless, suffocatingly toxic and poisonous gas. When it is dissolved in water, it forms sulphuric acid. Sulphur oxide is used in the production of sulphuric acid, as a bleach and as a preservative in some foods.

Sulphurous acid (H2SO3)

Sulphurous acid is a weak acid which is found in solution only. It is a product of the dissolving of sulphur oxide in water.

Sulphuric acid (H2SO4)

Sulphuric acid is a viscous, colourless, very corrosive acid. Concentrated sulphuric acid contains 2% water. It is a very strong oxidising agent and is often used to rid a system of water (it is very hygroscopic). Sulphuric acid is a strong acid. More negative metals than hydrogen dissolve in it, forming a salt and water. A dilute solution will not dissolve copper. A more concentrated solution, however, will dissolve copper, oxidising it at the same time.

Chemists come across two terms which are oft-used in the field: sulphates and sulphides. As one might guess, both terms have something to do with sulphur. Sulphates and sulphides are the salts of sulphuric acid, derived from sulphur hydrides. Sulphates are salts which arise from the reaction between a metal and sulphuric acid. Sulphides are compounds which are the product of the reaction of a metal with sulphurous acid. Sulphates have one sulphur atom bonded to four atoms of oxygen. Sulphides have sulphur atoms which are not attached to any oxygen atoms.

Sulphates are solid materials composed of sulphur and metal atoms which contain the sulphate ion, chemical formula (SO4- ) and one metal cation. These types of compounds are widespread in nature (for example CaSO4 – calcium sulphate, also known as gypsum).

Sulphides contain a sulphur anion and the cation of a metal (for example iron sulphide, FeS).

Sulphuric acid is produced through a process known as contact oxidation. The reaction mechanism has pure SO2 oxidising at 500° C under the influence of a vanadium catalyst. The cooled gas is led through a 98% solution of sulphur acid. The compound SO3 is absorbed, to create H2S2O7. By diluting with water, sulphuric acid of the desired concentration is produced.

Sulphuric acid is used in the production of some fertilisers and nitrogen-containing compounds, as well as some phosphoric compounds and the salts of acids. It is also used in the production of storage and other batteries.

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Phosphorus, phosporic acid and its salts

Besides nitrogen, phosphorus is the most important element found in the fifth main group of the period table (Group VA). It has five electrons in its outermost shell. Phosphorus is a solid at room temperature. It is found in a number of what are called alotropic modifications: For example, there is red phosphorous and white phosphorous. It is also found in the bodies of both animal and human hosts, in the compound calcium phosphate.

White phosphate is an oily, poisonous substance which has a characteristic odour. It burns in air, so it has to be stored under water. When heated in the presence of oxygen, it changes into the less reactive red phosphorous. Red phosphorous forms 4-atom molecules and is soluble in fats and oils.

When heated, it reacts slowly to form phosphorous oxide. In so doing, energy is released which radiates in the presence of light. This is the characteristic gleam of white phosphorous in the dark, which has led to glowing materials being called phosphorous. The name phosphorous, then, derives its original meaning from the Latin root which means ‘carrier of light’.

Red phosphorous is a red, soft crystal. It is not poisonous. It does not burn in air. It is composed of an unending chain of phosphorus atoms. It is completely and totally insoluble. Red phosphorus is used in the production of matches.

When red or white phosphorous is burned, a white solid material is formed. This is phosphoric oxide, a strongly hygroscopic reagent which reacts strongly with water and can produce phosphoric acid, which is used to protect some materials from corrosion.

Phosphoric acids are those which come from phosphorus derived from oxygen-containing acids. Phosporic acids are relatively strong and non-volatile. They have a pleasant-smelling odour and are non-toxic. When added to some drinks, they are taste boosters, making these drinks have more intensive tastes. They are produced by dissolving phosphoric oxide in water.

Phosphoric acid (H3PO4) is the most important of all of the phosphorous-containing acids. It is found in numerous physiologically important compounds (for example in DNS). Besides the better-known H3PO4, there are other phosphorous-containing acids such as H3PO3 which is produced as an intermediate in the dissociation reaction with water at a temperature of over 200° C.


Phosphates are salts of the phosphoric acid family, especially those of the ortho phosphorous acids. Because these have three hydrogens included, they can be replaced. There are, therefore, three degrees of phosphates which can be derived from this group of phosphoric acid.

Primary phosphates have just one atom of hydrogen replaced by a metal, giving the chemical formula

MH2PO4. Secondary phosphates have two atoms of hydrogen replaced by two atoms of metal, giving the chemical formula M2HPO4. Tertiary phosphates have all three of their hydrogens replaced, resulting in the chemical formula M3PO4.

Heating results in primary and secondary phosphates being transformed into metaphosphates (with rings in the molecules) or to high molecular polyphosphates. These phosphates are most often used in the production of wash powders or as water softeners.

There are relatively large beds of phosphates found in nature. These are often transformed into fertilisers.

The esters of acidic orthophosphates are also called phosphates. These are often used to repel pests. They can also, however, be used as intermediates in the material transport of some organisms.

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Ammonia and ammonium-containing compounds

Ammonia (NH3) is one of the most important and most fundamental chemical compounds. There are three atoms of hydrogen bonded to one atom of nitrogen in a molecule of ammonia. The three bonds are all polar in nature, thanks to the differing electronegativities of N and H. The ammonia molecule has a pyramidal structure.

Ammonia, a colourless gas, has a repellent stench. It can be dissolved in water to a great degree. At room temperature, one litre of water can dissolve 700 litres of ammonia. Ammonia corrodes and is poisonous. Ammonia can be liquified rather easily. Liquid ammonia is colourless and behaves similarly to water, because molecules of ammonia create dipoles thanks to their polar bonds. With acids, ammonia forms ammonium salts.

In the laboratory, ammonia can be produced by the reaction of a concentrated solution of sodium hydroxide and ammonium chloride.

NH4 + CL + Na + OH ® NH3 + H2O + Na + Cl

Ammonia is easy to recognise in its gaseous state because of its distinctive odour. An indicator can be used to determine whether ammonia is present in an aqueous solution. If so, the paper indicates base. We get the same alkaline reaction when indicator paper is subjected to the effects of an ammonia pair. When reacted with hydrogen chloride, ammonium chloride is formed. This reaction can be recognised because of the formation of white smoke.

NH3 + HCl ® NH4Cl

Synthesis of ammonia

Ammonia can be synthesised from the elements nitrogen and hydrogen in what is known as the Haber-Bosch reaction. After years of experimentation, the technology finally developed, and in 1909, F. Haber and C. Bosch started getting close to their dream. A few years later, the synthesis had been performed successfully (F. Haber won the Nobel Prize in 1918 for the feat). An equilibrium reaction, in the presence of a catalyst, resulted in the formation of ammonia. In order to make the reaction work effectively, high temperature and high pressure are needed.

3H2 + N2 ® 2NH3

The opposite reaction is highly exothermic. When it is carried out, there is a significant loss of volume as a result. According to Le Chatelier’s principle, when a force or outside variable in introduced into a system in equilibrium, that system will act to create a new equilibrium under the new conditions. The least boost to the above reaction, therefore, leads to an increase in the product side of a synthetic reaction. With the help of a catalyst, the activation energy of the reaction is greatly reduced. Still, the hydrogen present only begins to react with nitrogen at any significant rate at temperatures of 450 - 500° C. and in the end, the mixture of products formed contains only up to 20% ammonia. This is separated out from the rest of the liquids, and the unused gases can be reused. Iron, and some of its various oxides, are used as a catalyst.

Production of the ammonium ion

Ammonia reacts with water to produce the ammonium ion and a hydroxide ion. In this reaction, one atom of hydrogen bonds to the lone electron pair of the original ammonia compound NH3. A proton, then, is transferred.

NH3 + H2O ® NH4 + OH

Because this is also an equilibrium reaction, besides molecules of water and ammonia which were in the solution to begin with, there are ammonium ions and hydroxide ions present, too. The solution behaves in an acidic manner. It is called a solution of ammonium water.

Ammonium salts

The reaction of ammonia or a solution containing ammonium ions with an acid results in the formation of a salt, which can be called an ammonium salt. These have an ionic lattice.

Ammonia plus hydrogen chloride ® ammonium chloride

NH3 + HCl ® NH4Cl

Ammonia plus sulfuric acid ® ammonium sulphide

2NH3 + H2SO4 ® (NH4)2SO4

Ammonia plus nitric acid ® ammonium nitride

NH3 + HNO3 ® NH4NO3

Ammonia and hydrogen chloride are dissociated from ammonium chloride, the reverse of the first reaction above, which is the synthesis of ammonium chloride. The hydroxide compounds of alkaline metals and alkaline earth metals and ammonium salts break down, or dissociate, into free ammonia.

Ammonium salts are used in nitrogen and other mineral fertilisers.

Nitric acid

Nitric acid is a an oxygen-containing acid composed of nitrogen. Pure nitric acid is a colourless liquid. It forms an azeotropic mixture with water. This type of azeotropic mixture should have the same boiling point if it is mixed in the same relative mixture in both mixed fractions. For this reason, the mixture cannot be separated by distillation. In the presence of light, the compound breaks down into oxygen and nitric oxide. Nitric acid was earlier called aqua regia, something similar to the king of the solvents, because all of the metals besides gold dissolve in it. Nitric acid is produced using the Oswald process: Ammonia reduces in air at a temperature of 780-940° C with the help of a platinum catalyst to produce nitric oxide. This compound gradually breaks down to NO2. When water is allowed to react with this compound, nitric acid (HNO3) is the result.

Nitric acid is used in the production of nitric fertilisers and as a nitric and oxidation agent in the chemical industry.

In nature, the nitric group is found exclusively in the form of salts, or nitrates. Nitrates are salts of nitric acid which contain the NO3 group. They are found most often in the form of ionic crystals which are water soluble. As a matter of fact, all nitric salts are water soluble - without exception. Besides fertiliser, they are used for their explosive character in fireworks.

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Nitrogen and its compounds

Nitrogen (Latin nitrogenium) is the first element of Group V main group elements, a group that is called the nitrogen group. The nitrogen atom has five electrons in its outermost electron shell. Nitrogen is a colourless, odourless gas which is found as a two-atom molecule in nature (N2). The two nitrogen atoms are joined by a triple bond. Each nitrogen atom has one unbonded electron pair.

Nitrogen was recognised as one component of air in 1777 by C.W. Scheele. At the time, it was found not to be essential for either combustion processes or organism respiratory functions. It is almost completely insoluble in water. It does make up around 78.1% of the Earth’s atmosphere. Besides being part of the air that we breathe, nitrogen is found in various other compounds, as nitrates bonded with, among others, sodium and potassium, as in the molecule potassium nitrate (KNO). Nitrogen, however, is generally not very reactive.

Pure nitrogen is produced by the liquification of air (Lindeo process). Air is compressed and the heat which results is removed from the system. If the air is to expand again, the gas molecules present need to be supplied with energy, to get them moving again. Instead, the heat of the system is removed. The gas cools down gradually, finally changing into a liquid. Nitrogen can be separated from the liquid air mixture using fractional distillation. Nitrogen can also be won when the oxygen component of air is removed through reaction with some other material.

Because nitrogen is not very reactive, it is often used as a protective, non-interfering gas in industry. In its liquid form, it is used as a cooling agent in the freezing of some dried, processed foods, often when those foods are canned. As a gas, nitrogen is a raw material in the production of nitrogen-based compounds like ammonia and nitric acid. Nitrogen is one of the most important components of both

plants and animals, because it is included in all protein molecules. Molecular nitrogen which is found in the atmosphere cannot, however, be used as a foodstuff. Plants, then, must take nitrogen in through its salts, through plants’ roots. For this reason, the production of nitrogen-based fertilisers is extremely important for a plant’s health and well-being.

Nitrogen-containing compounds which appear in nature

In the Earth’s atmospheric system, 90% of the nitrogen present is in the gaseous state. Just one percent is found in bonded, compound form on the Earth’s surface, or in the bodies of living organisms. When it is found on the Earth’s surface, nitrogen is mostly in the form of the ammonium and nitrate ions. Living organisms contain nitrogen mostly in the form of amino acids, peptides and proteins. There is also nitrogen to be found in the form of sodium nitrate, so-called Chile saltpetre, or in potassium nitrate, also called Indian saltpetre, the latter in large quantity.

The nitrogen-containing salts found in the Earth’s crust are taken in by plants through their roots and are later used in the production of amino acids, proteins and other compounds. Plants are primary producers of organic nitrogen compounds. All animals, including the human animal, must meet their nutritional needs, in a direct or indirect way, by ingesting some form of plant material. Once used, nitrogen is freed from the compound it was included in, often when that organism’s organic material begins to decay, in the form of ammonia. Nitrifying bacteria then change ammonia to nitrates which can be reingested by plants.

The nitrogen cycle

Nitrogen is a vital raw material in the lives of all living organisms, if only in small doses. Animals and human beings get their nitrogen from plants, not being capable of taking it in directly from the atmosphere. Most plants take in nitrogen in the form of the ammonium ion or in nitrate ions from the ground. The nitrogen which occurs in the atmosphere is bonded by several symbiotic microorganisms (nitrogenous bacteria of legumes, fungi in the root systems of alders) and transferred into the host plant. The nitrogen dioxide which is formed in thunderstorms also makes its way into the ground. This is how nitrogen, in the form of ammonium and nitrate ions, makes its way into the food chain: through the root systems of plants. After the microorganisms that brought it into those root systems die, and nitrogen is freed from the proteins which contained it in the form of ammonia, again by the actions of microorganisms. Part of this is then once again changed by bacteria to ammonium and nitrate ions... These are once again taken in by plants... Other ammonium is used by the denitrifying bacteria, changing it to molecular nitrogen, which is then returned to the atmosphere.

The compounds of nitrogen which do reach humans and other animals are later broken back down and released as decomposed matter which returns to the Earth. There, plants and microorganisms take over once again.

The effect of human beings on the natural nitrogen cycle

The necessity of feeding the world’s growing population has led to more intensive agricultural practices in recent years, and the depletion of a great amount of farmland. The harvests of some plants have shown them to be low in nitrogen, as well as other phosphorous and potassium-containing compounds. In order to produce enough high-quality food for the world, the foods that are grown need to be supplied with enough fertiliser. In the past, manure, compost and even peat were used. Now, artificial fertilisers have come into fashion, because of the fact that they do contain the nutrients that crops need - and in sufficient concentration.

Yet plants cannot take in too much of this artificial fertiliser. A significant amount of it, therefore, gets into underground water supplies, which increases the amount of ions, or the hardness, in our drinking water. The materials contained in fertilisers are dangerous for human health. Unused fertiliser gets into our seas and rivers, causing the eutrophisation of the water (water plants grow too quickly and use all of the oxygen available in the water, leading to water animals and plants dying for a lack of oxygen). With more and more traffic on the freeways, more and more carbon dioxide is being pumped into the atmosphere. This makes breathing more difficult and is causing the extinction of the rain forests, as well as increased pollution and the harming of trees. In addition, nitrogen concentration in the atmosphere is decreasing, thanks to the synthesis of ammonia.

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