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Encyclopedia about Chemistry

 

Production of iron and aluminum

Another use of electrolysis is the purification of pure metals from their ores. A supply of electrical current can work to spark an oxidation or reduction process, so that materials can be extracted from their electrolytic solutions, or from a mix of molten metals. In this way, materials can be won in their pure form. Besides the electrolysis of an aqueous solution, an electrolysis can be performed on a molten mass of metals. Technically, electrolysis processes can be used to purify sodium and aluminum from a molten mass.

Aluminum is one of the most prevalent metals on Earth. Yet it is a complicated process to win pure aluminum from its mixtures. Crude aluminum is found in nature most often as a component of bauxite.

The process of purifying aluminum can be divided into two phases.

Starting with bauxite, we use the Bayer process to gain aluminum in the following manner: Bauxite is allowed to react with sodium hydroxide, a base. This leads to the release of aluminum into solution in the form of aluminum hydroxide. After filtration, the aluminum is separated from the hydroxide ions as aluminum hydroxde. This is filtered off, and when heated, calcination takes place. The result is the production of an aluminum oxide compound.

This aluminum-containing product is put under electrolysis, forming pure aluminum and hydrogen. The electrolysis of a stream of molten metal means that the metal will be separated from a molten mixture of salts of the metal at high electrical current but low voltage.

Iron is known as a transition metal found in the fourth period of the periodic table. In its pure form, it is white, relatively soft and magnetic. In nature, it is usually found combined with other atoms, in compounds. Hematite is one of is most important ores. Iron is separated from its ores in large ovens.

In order to win iron, industrial furnaces are necessary, as are an iron ore, limestone and carbon. The necessary materials are placed in a large oven. The oven has a ventilation system to allow air to circulate. The heating of limestone results in the creation of a calcium oxide.

  1. The oxygen in the air reacts with carbon, producing carbon dioxide.
  2. At very high temperatures, this carbon dioxide reacts with oxygen to produce carbon monoxide.
  3. Carbon monoxide reduces iron in the ore to pure iron, as in the reaction Fe2O3 + 3CO = 2 Fe + 3CO2

The gases produced are called exhaust gases and are released through the chimney of the industrial furnace.

The impurities, called slag, are lighter than the iron produced, so they can be separated, from the bottom to the surface of the iron. In the lower part of the industrial furnace, crude iron is produced. Crude iron contains around 2-5% carbon and 3-4% slag. In this state, iron can be used for casting or for forging. Otherwise, it is possible to use further chemical processes to produce steel.

Steel is made of iron and a certain amount of carbon, not to exceed 1.5% of the total. Carbon makes steel harder, while lowering its malleability. Other metalloids may also be added in, so that steel can attain its usual properties. For example, steel can contain as much as 11-14% chromium.

According to the latest steel production processes, slag additives and scrap iron are added to the molten mass of crude iron. The addition of oxygen works to improve the oxidation of impurities and helps to clean up the steel.

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The composition of air and its pollutants

No matter where we are on our planet, the Earth, we are surrounded by the atmosphere, or air. Air, however, should not be confused with oxygen. Oxygen is just one of the components of air. There are others. Air is composed of the following:

77.1% nitrogen

20.8% oxygen

1.1% water vapor

0.9% argon

0.1% other gases (hydrogen, carbon dioxide, noble gases…)

The proportions of these gases does not usually change in any significant manner, although the concentration of carbon dioxide or sulfide compounds in the air above big cities and industrial centres can increase dramatically in a rather short period of time.

Pollution of the atmosphere

We human beings have a greater influence on the environment we live in than any other organism that has walked this Earth in all its long history. It is true that natural systems can lead to the pollution of the Earth’s atmosphere, of course. For example, the breakdown of organic matter can lead to the release of some poisonous gases into the atmosphere. Plants can breakdown these pollutants, producing oxygen from the poisonous carbon dioxide.

But the plant world is not capable of breaking down and transforming all of the pollutants which are being produced today. In addition, the world’s forests are being destroyed in order to obtain the large spaces needed for a demanding, growing human population whose needs are growing, too. With a quickly growing population on the Earth, more and more harmful pollutants are being produced. As of now, there is no way known to neutralise or get rid of these pollutants.

The only sure way to protect the environment is to develop chemistry and its processes in such a way that the consumer goods and processes that release harmful pollutants into the air are replaced by other, less harmful ones to the environment. For example, in the last few years, freon, which was used as an ingredient in sprays and as a refrigerant in refrigerators, has been replaced, because it was found to harm the ozone layer.

No solution has yet been found to the problem of the greenhouse effect. The sun’s rays are reflected off of the Earth, only to return to the atmosphere. Gases in the atmosphere, first and foremost carbon dioxide, act as a greenhouse to hold some of that heat in the Earth’s atmosphere. Of course, it should be pointed out that the greenhouse effect, in a more natural setting, is a natural phenomenon which renders life on Earth possible.

In the 20th century, however, the oxidation of carbon dioxide has risen dramatically, thanks to the burning of fossil fuels (organic: coal, oil, natural gas) and the burning of the rain forests. This artificial and rapid increase in the concentration of carbon dioxide in the air, some scientists have concluded, could raise the Earth’s average temperature. This phenomenon is called global warming. If the Earth’s average temperature does continue to rise as it has done in the last few decades, the polar ice caps could melt. Complete melting of both polar ice caps would raise sea level a few hundred metres, and reduce humanity’s, and the Earth’s, livable habitat in a fundamental way. The end result could be the destruction of many habitable landscapes, as well as the environment of the plants and animals which still inhabit the Earth.

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Water, hydrogen

Pure water is composed of just two atoms, oxygen and hydrogen, one atom of the former, two of the latter. Water is colorless, but it can appear as a blue liquid at its surface. At normal air pressure, water freezes at 0° C. Its boiling point is 100° C. The density of liquid water is at its highest value at 4° C. For that reason, ice floats on water, and water freezes at its surface first. When frozen, water, now ice, increases its volume by around 9% . Because of this property, leaving water in some type of container on a cold day could lead to that container breaking or cracking.

Water is the most common compound found on Earth, covering 71% of its surface. The atmosphere is made up of 4% water vapour. Most living organisms are composed of about 60-70% water, and some living organisms are composed of up to 98% water (seaweed). Water is never found in its pure form in nature. It always contains some dust or other chemical impurities. Water which, after boiling the liquid away leaves more than 1 g of residue, is considered to be freshwater. If, however, after boiling away the liquid portion of water more than 1 g of residue is present, this water is considered to be saltwater. Of the Earth’s water, around 95% is saltwater (after boiling off of water portion more than 1 g of residue remains).

The hardness of water can be determined. This property depends on the amount of calcium, magnesium and other ions dissolved in the water. When water is distilled, these ions are removed, and the water, more pure than usual, can be used in chemistry and medicine. The distillation process involves boiling off the water. The water’s impurities do not boil off if they have a higher boiling point than water, instead remaining in the original vessel which contained the water. The water vapour then condenses, producing liquid water which is now purified. Neither people nor other living organisms should drink distilled water, however. This would cause them problems. Drinking water contains minerals that living organisms need. It should, of course, be free of harmful bacteria.

Water has another chemically important characteristic. Water molecules can hydrogen bond with each other. This type of bonding between oxygen and the hydrogens in another molecule of water is not the type of bond in which electrons are shared. Oxygen attracts the negatively charged electrons more strongly than hydrogen, giving oxygen a partial negative charge and hydrogen a partially positive charge. Electrostatic forces then take over. The water molecules align themselves in a way which has the oxygen atom in one water molecule lined up next to the hydrogen atoms in another molecule. This creates an electrostatic force between two water molecules. A structure of alternating charges is thus created. These weak forces between water molecules are the basis of surface tension. Hydrogen bonds are also responsible for water’s relatively high melting and boiling points.

Hydrogen is found in almost all compounds, whether they are inorganic or organic. It is by far the most common element in the universe. In its elementary form, it is a colourless, odourless flammable gas. It burns with a blue flame.

Uses of water

Water is important for living organisms as a transport mechanism for needed materials including gases, and to keep up needed pressure in cells. In plants, water is an important component of photosynthesis. It is also an important solvent, refrigerant and transport mechanism in everyday life. It is especially important in chemistry. Many materials could not be studied without the help of water, because of these materials’ reactivity in water. Salts, acids and bases are almost always studied as solutions in water.

When preparing water as the product of a chemical reaction, it is necessary to realise what purpose the water is going to be used for. Chemical and physical processes can be used to produce for example drinking water from surface or underground water, or to produce water which does not contain any iron or manganese. Or, soft water can be made, to be used in breweries, paint factories and textile factories. The most important processes are separation, filtration and distillation. Using these processes, unwanted components of water can be separated.

The water chain on Earth

Water movement around the Earth can be described exactly using water chains. From bodies of water such as lakes and oceans, from land, from living organisms, even from rain, water is constantly evaporating. After cooling in the highest reaches of the atmosphere, this water falls to the Earth again, as precipitation, onto dry ground but also into rivers, lakes, seas and oceans. Then, plants use some of the water which has fallen as rain. The rest of the water is transferred from dry ground to the Earth’s rivers, seas and oceans.

Water pollution

Another environmental problem is caused by water pollution. The ever increasing use of foreign materials which do not occur naturally leads to water pollution. These foreign materials, also called pollutants, get into our water through canalisation and trash. The processes are varied, the result the same: water pollution. Water which escapes from waste dumps, and acid rain, can cause water sources to become polluted. Living organisms are capable of getting rid of a number of harmful materials on their own, as long as they occur in relatively small amounts, and the influx into their bodies is slow. Otherwise, if a harmful concentration of pollutants is infused into a living organism, that organism can die, especially if it lives in or near polluted water. Even those organisms which are capable of removing harmful pollutants from their bodies can be threatened if a high concentration of pollutant is introduced. Laws and conscientious behaviour are helping to avoid a catastrophe in the oceans and other water sources of the world. At least, we are trying to limit the scope of individual catastrophes. Chemistry, of course, has its own important role to play in the battle.

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Alkaline metals, Alkaline earth metals, sodium

The alkaline metals include lithium, sodium, potassium, rubidium, cesium and the radioactive francium. All of these elements are metals. All have one electron in their outermost shell. They are members of the first main group in the periodic table, IA.

Alkaline metals do not appear in nature in the elemental state, but rather always as compounds. All of the elements in the alkaline metal group have similar characteristics which are derived from their similar electron configuration. Like all elements in the same group, they share many of the same properties. These common group properties are not exactly the same from element to element, however. They change with increasing atomic mass (for example, hardness, burning temperature, melting and boiling point). The high reactivity of the alkaline metals is the result of their having one electron in their outermost shell. The reaction of one of these, or its oxide as the case may be, results in the formation of a hydroxide, a compound which has basic character.

When atoms react, the most important factor in how they behave is the number of electrons in their outer shell. These electrons are called valence electrons. They can form chemical bonds with other atoms. When this happens, an electron must be transferred, that is, donated or accepted, to or from the outermost electron shell of another atom. Alkaline metals have only one valence electron, and they always donate this one electron when they form chemical bonds. For this reason, all elements in this group can attain an oxidation state of +1, meaning that they have given up their one electron.

The elements of the second main group of the periodic table are called the alkaline earth metals. Their chemical properties are also similar to each other, and their physical properties are based on a few basic laws. Beryllium, magnesium, calcium, strontium, barium and radium are all Group IIA elements. They all have two electrons in their outermost electron shell. For this reason, they are not as reactive as the elements of Group IA. They are all metals.

The most important alkaline earth metal is sodium. This element has great significance in both the compounds which it naturally occurs in, and those which can be made synthetically. Sodium is a component of table salt, and of the dough which makes bread. It is a component of many strong bases and of soap, to mention just a few.

Formation of table salt

When two atoms of sodium join with one molecule of chlorine (Cl2), the one lone electron in sodium’s outermost electron shell is transferred to one chlorine atom. The chlorine atoms separate from one another, then join with one atom of sodium each to form two new molecules of sodium chloride, which crystallise, in the reaction 2Na + Cl 2NaCl. When the sodium atom’s electron is transferred, a positively charged sodium ion (cation) is formed. When chlorine captures that transferred electron, a negatively charged chlorine ion (anion) is formed. These are mutually attracted to each other. The formation of these ions allows both atoms (now ions) to reach a stable electron configuration in their outer shells, a noble gas configuration.

Electron arrangement can be thought of as an octet, as formulated by G.N. Lewis and W. Kossel. According to this theory, electrons are donated and accepted in such a way so that the atoms they belong to reach a noble gas configuration, one in which an octet of electrons is present in the valence shell of an atom. This is the energetically most advantageous state for any element. Often, reactions which lead to this electron configuration can be quite violent in nature. The release of reaction heat is one of the results of the reaction of sodium ions with chloride ions. Molecules of sodium chloride are regularly arranged in an ionic lattice. The crystals which are produced are cubic.

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Halogens

The halogen group of elements

Elements in this group include fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At) – an element which is not naturally occurring and can be prepared only in the laboratory. Because these elements have seven electrons in their outermost shell, they are members of the main group VIIA. They all share similar characteristics. In nature, halogens are found mostly as the negative components of salts. They are non-metals. Halogens are very reactive. They react with hydrogen to form a hydrogen-halogen compound. Oxides (compounds containing oxygen) are acidic in character. Halogens join with metals to form ionic bonds. The properties of halogens differ as a function of increasing atomic mass. The state of matter of individual group members changes from gaseous (flourine and chlorine) to solid (iodine and astatine). In the gaseous form, halogens always form two atom molecules (F2, Cl2, Br2). With increasing atomic mass, melting and boiling point rise, as does density. Solubility in water decreases as atomic mass grows.

Halogens often occur in nature bonded in salts. From these salts, pure halogen elements can be produced. These pure elements have many uses, first and foremost as raw materials in the chemical industry. They are ingredients in fertilisers, and they are used in medicine. These elements are important trace elements for living organisms (fluorine as an ingredient in toothpaste and bones). In addition, halogens are significant raw materials for the production of artificial substances (fluorine, chlorine). Pure crystals of fluorine can be used in the semiconductor industry. Iodine containing salts are used in some medicines and grocery products. Chlorine is often used to treat water, both drinking water and water for other uses.

Halides

Halides (hals = Greek for salt, gen = Greek tribal word for produce) are produced by the synthesis of metals and halogens. If glowing iron comes into contact with a copper wire coated with chlorine, these elements react violently to produce an iron chloride or copper chloride compound. Halides are salts. The salts of bromine are called bromides, the salts of chlorine chlorides (fluorides, iodides). When halides are formed, electrons are transferred between individual atoms. Thus, ions are formed which have the characteristic ionic lattice. The ions of the various halogens have the same arrangement as the ionic lattice of sodium chloride. For this reason, this typical structure is called the sodium chloride ionic lattice. Ionic lattices produce ionic crystals. The formula NaCl describes the smallest building block of an ionic lattice. We call this crystal a unit lattice.

Halides are easily soluble in water and other polar solvents (those which have polarly arranged molecules). When halogens are dissolved, electrically charged ions are released into solution. If we dissolve sodium chloride in water, freely moving positively charged ions of sodium (cations) and negatively charged ions of chlorine (anions) are released into solution. Ions are carriers of charge, so ionic solutions are able to conduct an electrical current. When solid halides are heated and melt, they move to the liquid state of matter, called a molten melt. Even these molten melts can conduct an electrical current.

Materials whose makeup is difficult to determine are investigated through spectroscopy. The principle of using a mass spectroscope is that a gaseous sample of some material is placed in a tube, where it is bombarded with electrons. The material is ionised (charged), and ions move to the end of the tube, where an oppositely charged electrode is placed. A magnetic field is created in the tube, and ions are separated according to their mass. On a detection screen, these ions are divided in such a way depending on their mass.

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