My Science School

The earth itself is a store of energy, as the rocks inside it are extremely hot. Water in underground streams and lakes can be heated by running over hot or molten rock. It may then come to the surface in hot springs or geysers. In some parts of the world the hot water or steam is used to turn turbines to produce electricity. This is called geothermal energy.

This key renewable source covers a significant share of electricity demand in countries like Iceland, El Salvador, New Zealand, Kenya, and Philippines and more than 90% of heating demand in Iceland. The main advantages are that it is not depending on weather conditions and has very high capacity factors; for these reasons, geothermal power plants are capable of supplying baseload electricity, as well as providing ancillary services for short and long-term flexibility in some cases.

There are different geothermal technologies with distinct levels of maturity. Technologies for direct uses like district heating, geothermal heat pumps, greenhouses, and for other applications are widely used and can be considered mature. The technology for electricity generation from hydrothermal reservoirs with naturally high permeability is also mature and reliable, and has been operating since 1913. Many of the power plants in operation today are dry steam plants or flash plants (single, double and triple) harnessing temperatures of more than 180°C. However, medium temperature fields are more and more used for electricity generation or for combined heat and power thanks to the development of binary cycle technology, in which geothermal fluid is used via heat exchangers to heat a process fluid in a closed loop. Additionally, new technologies are being developed like Enhanced Geothermal Systems (EGS), which are in the demonstration stage.

To promote wider geothermal energy development, IRENA coordinates and facilitates the work of the Global Geothermal Alliance (GGA) – a platform for enhanced dialogue and knowledge sharing for coordinated action to increase the share of installed geothermal electricity and heat generation worldwide.

A joule (J) is a small unit of energy. More commonly, we measure energy in kilojoules (kJ), which are units of a thousand joules each. A medium orange probably contains about 250kJ of chemical energy. The same weight of chocolates might contain 1700kJ of energy.

When we raise an apple up to a height of one meter, we perform approximately one joule of work. So what is a joule? Joule is the unit of energy used by the International Standard of Units (SI). It is defined as the amount of work done on a body by a one Newton force that moves the body over a distance of one meter. Wait a minute … is it a unit of energy or a unit of work?

Actually, it is a unit of both because the two are interrelated. Energy is just the ability of a body to do work. Conversely, work has done on a body changes the energy of the body. Let’s go back to the apple example mentioned earlier to elaborate. An apple is a favorite example to illustrate a one joule of work when using the definition given earlier (i.e., the amount of work done ….) because an apple weighs approximately one Newton. Thus, you’d have to exert a one Newton upward force to counteract its one Newton weight. Once you’ve lifted it up to a height of one meter, you would have performed one joule of work on it.

Now, how does energy fit into the picture? As you perform work on the apple, the energy of the apple (in this case, its potential energy) changes. At the top, the apple would have gained about one joule of potential energy. Also, when the apple is one meter above its original position, say the floor, gravity would have gained the ability to do work on it. This ability, when measured in joules, is equivalent to one joule.

Meaning, when you release the apple, the force of gravity, which is simply just the weight of the body and equivalent to one Newton, would be able to perform one joule of work on it when the apple drops down from a height of one meter.

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Energy from the Sun is stored in the leaves of plants, but it is also possible to store electrical energy in batteries. Inside a dry-cell battery there is a chemical paste called an electrolyte (which contains charged particles), a positive terminal (or electrode) and a negative terminal. When the battery is put into an electrical circuit, chemical reactions cause electrons to flow out through the negative terminal, through the circuit, and back through the positive terminal. When all the chemical reactions have taken place, the battery is “dead” and has to be replaced or, in the case of some batteries, recharged.

Human beings have been looking for a good way to store energy for a long time. One of the major things that has been holding up electric cars is battery technology -- when you compare batteries to gasoline, the differences are huge. For example, a typical electric car might carry 1,000 pounds (454 kg) of lead-acid batteries. Those batteries take several hours to recharge, and might give the car a 100-mile (160-km) range. Two or 3 gallons of gasoline give the same range, weigh less than 30 pounds (13 kg), and you can pump that much gasoline in about a minute. 

Here's a list of other technologies that people commonly used to store energy. Some of these work in an electric car, while others are better for stationary applications:

Imagine a world where everything that used electricity had to be plugged in. Flashlights, hearing aids, cell phones and other portable devices would be tethered to electrical outlets, rendering them awkward and cumbersome. Cars couldn't be started with the simple turn of a key; a strenuous cranking would be required to get the pistons moving. Wires would be strung everywhere, creating a safety hazard and an unsightly mess. Thankfully, batteries provide us with a mobile source of power that makes many modern conveniences possible.

While there are many different types of batteries, the basic concept by which they function remains the same. When a device is connected to a battery, a reaction occurs that produces electrical energy. This is known as an electrochemical reaction. Italian physicist Count Alessandro Volta first discovered this process in 1799 when he created a simple battery from metal plates and brine-soaked cardboard or paper. Since then, scientists have greatly improved upon Volta's original design to create batteries made from a variety of materials that come in a multitude of sizes.

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Our energy comes from the Sun — but not directly. Plants convert sunlight into chemical energy. We then eat the plants or other animals that have fed on them, so the chemical energy is stored in our bodies. For this energy to be released, chemical reactions need to take place in our bodies. These reactions require oxygen, which we take in from the air we breathe. That is why we get breathless when we are running and turning a lot of chemical energy into kinetic energy.

Energy can be found in many things and takes many forms. There is potential energy in objects at rest that will make them move if resistance is removed. There is kinetic energy in objects that are moving. The molecules making up all matter contains a huge amount of energy, as Einstein's E = mc^2 pointed out to us. Energy can also travel in the form of electromagnetic waves, such as heat, light, radio, and gamma rays. Your body is using metabolic energy from your last meal as you read this. Energy is constantly flowing and changing form. If you take your metabolic energy and rub your hands together, you have made metabolic energy into mechanical energy. Your hands will heat up. That is some of the mechanical energy turning into heat energy.

So energy can change form, but where did that energy ultimately come from? Let's trace back a chain of events. A bicycle is rolling down the hill, transferring potential energy into kinetic (movement) energy. The bicycle got its potential energy (energy due to position related to gravity) by the rider using metabolic energy to move the pedals. The pedals used mechanical energy to move the chain, which moved the wheels. The rider's metabolic energy came from chemical energy that was stored in the molecules of the food she ate. That chemical energy entered the animal whose meat she ate by the animal digesting a plant and breaking the bonds in its molecules. The plant made the molecules by using light energy from the Sun. The Sun's light energy came from electrons in its atoms lowering energy states, and releasing energy. The energy in the atoms came from the nuclear reactions in the heart of the Sun.

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Coal, oil or gas may be used to fuel a power station. All of these are fossil fuels, formed millions of years ago when the bodies of plants and animals were crushed under enormous pressure. Electric Power Plants have a number of components in common and are an interesting study in the various forms and changes of energy necessary to produce electricity.

Boiler Unit: Almost all of power plants operate by heating water in a boiler unit into super-heated steam at very high pressures. The source of heat from combustion reactions may vary in fossil fuel plants from the source of fuels such as coal, oil, or natural gas. Biomass or waste plant parts may also be used as a source of fuel. In some areas solid waste incinerators are also used as a source of heat. All of these sources of fuels result in varying amounts of air pollution, as well as, the carbon dioxide (a gas implicated in global warming problems). In a nuclear power plant, the fission chain reaction of splitting nuclei provides the source of heat.

Turbine-Generator: The super-heated steam is used to spin the blades of a turbine, which in turn is used in the generator to turn a coil of wires within a circular arrangement of magnets. The rotating coil of wire in the magnets results in the generation of electricity. A generator converts the kinetic energy into electrical energy.

Cooling Water: After the steam travels through the turbine, it must be cooled and condensed back into liquid water to start the cycle over again. Cooling water can be obtained from a nearby river or lake. The water is returned to the body of water 10 -20 degrees higher in temperature than the intake water. Alternate method is to use a very tall cooling tower, where the evaporation of water falling through the tower provides the cooling effect.

The electrical energy is carried along wires to homes and factories, where it is converted into heat, light or sound energy by electrical appliances.

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Chemical energy is released when chemical reactions take place. It is stored in many different kinds of substances, such as foods and fuels. Kinetic energy is the energy of movement. An object that is being acted on by a force is said to have potential energy.

Types of energy can be categorized into two broad categories – kinetic energy (the energy of moving objects) and potential energy (energy that is stored). These are the two basic forms of energy. The different types of energy include thermal energy, radiant energy, chemical energy, nuclear energy, electrical energy, motion energy, sound energy, elastic energy and gravitational energy.

Thermal energy is created from the vibration of atoms and molecules within substances. The faster they move the more energy they possess and the hotter they become. Thermal energy is also called heat energy.

Chemical energy is stored in the bonds of atoms and molecules – it is the energy that holds these particles together. Stored chemical energy is found in food, biomass, petroleum, and natural gas.

Nuclear energy is stored in the nucleus of atoms. This energy is released when the nuclei are combined (fusion) or split apart (fission). Nuclear power plants split the nuclei of uranium atoms to produce electricity.

Electrical energy is the movement of electrons (the tiny particles that make up atoms, along with protons and neutrons). Electrons that move through a wire are called electricity. Lightning is another example of electrical energy.

Also known as light energy or electromagnetic energy, radiant energy is a type of kinetic energy that travels in waves. Examples include the energy from the sun, x-rays and radio waves.

Light energy is a form of electromagnetic radiation. Light consists of photons, which are produced when an object's atoms heat up. Light travels in waves and is the only form of energy visible to the human eye.

Motion energy – or mechanical energy – is the energy stored in objects; as objects move faster, more energy is stored. Examples of motion energy include wind, a flowing river, a moving car, or a person running.

Sound energy is the movement of energy through substances. It moves in waves and is produced when a force makes an object or substance vibrate. There is usually much less energy in sound than in other forms of energy.

Elastic energy is a form of potential energy which is stored in an elastic object - such as a coiled spring or a stretched elastic band. Elastic objects store elastic energy when a force causes them to be stretched or squashed.

Gravitational energy is a form of potential energy. It is energy associated with gravity or gravitational force – in other words, the energy held by an object when it is in a high position compared to a lower position.

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Although both feel painful, wasp stings are alkali and bee stings are acid. That means that it is best to treat them with acid and alkali substances respectively.  Although bee venom is slightly acidic and wasp venom slightly alkaline, the difference is largely coincidental. Neither insect relies on the pH of their venom for any destructive power.

A typical sting injects less than 50 micrograms of venom, so even quite concentrated acid or alkali would barely be noticeable. Instead, the venom comprises a complex cocktail of proteins that stimulate the production of the stress hormone cortisol, destroy cell membranes, raise the heartbeat and inhibit blood clotting. Bee and wasp venom differ in the specifics of the proteins involved but their general effect is the same. They certainly don’t neutralise each other: if you somehow managed to be stung by one of each on the same spot, you would just feel twice the pain.

Not all bees sting. Male bees cannot, and bees are not out to get anyone! They will only usually sting if they are provoked or feel threatened. Bees are generally non-aggressive animals. A wasp stings contains alkali with a pH of 6.9 which is light green and almost neutral .By pouring vinegar on it the sting can be neutralised. When it has neutrilised it will turn green which is pH 7.

Wasp venom contains a series of hydrophobic peptides, mastoparans and chemotactic peptides as major peptidergic components. The first major component in the venom is mastoparam. The peptides in the mastoparan family are tetradecapeptide amides which cause degranulation of the mast cells to release histamine from the cells, and act on the adrenal chromaffin cells to release catecholamines and adenylic acids.

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It is possible to measure the acidity or alkalinity of soil. Acid soils are usually found in peaty or forest areas, while alkali soils often occur where the underlying rocks are chalk or limestone. Most plants prefer a soil that is neither too acid nor too alkali, but some are only happy in a particular soil. Heathers and rhododendrons, for example, prefer an acid soil.

The pH scale indicates acidity or alkalinity. A soil with a pH number below 7 is acid, while one with a pH above 7 is alkaline. Garden plants typically grow best in neutral or slightly acid soil (pH 7 or slightly below). Most won’t thrive in highly acid or highly alkaline soil, though a few have adapted to such extremes. In general, some nutrients cannot be efficiently absorbed by plant roots if soil pH is too high. If it is too low, on the other hand, nutrients may be taken up too efficiently: the excess cannot be processed fast enough and overloads a plant’s system, causing it to languish and die.

Local climate gives you a clue to the likely soil pH. In high-rainfall areas, soils are often acid. It’s in these regions that you tend to find acid-loving plants like azaleas, rhododendrons, camellias, and blueberries. Alkaline soils, in contrast, are typically found in low-rainfall areas. Many of the plants popular for waterwise gardens–sorts that need little water once they are established–do well in soil on the alkaline side. The olive, native to the Mediterranean basin, is one example of a plant that thrives in alkaline soil; oleander (Nerium oleander) and pomegranate also perform well.

Lime, available in either ground or powdered form, is often suggested to raise pH. Ground limestone is the slightly less potent of the two and raises pH more slowly. The amount needed depends on the soil texture (more is needed for clay than for sandy soil, for example) and other factors. Wood ashes and oyster shell also make acid soil more neutral.

To lower pH, common sulfur is the least expensive choice, though ferrous sulfate and aluminum sulfate are sometimes recommended instead. Ferrous sulfate, which also adds iron to the soil, is of the most help to plants that show yellow leaves as well as overall poor health. You’ll also lower the pH of alkaline soil over time by regularly applying organic amendments such as compost and manure.

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Many products and processes require the use of acids and alkalis. Here are just some of them. Car batteries contain acid. Acids are also used to make fertilizer, paint, detergents, plastics, dyes and some artificial fabrics. Alkalis are used in the manufacture of soap, floor cleaners, indigestion tablets and cement.

The most commonly made industrial chemical in the world, sulphuric acid has numerous applications across industries. Companies make it as a precursor to phosphoric acid, which, in turn, finds use in detergents and phosphate fertilizers. However, if it gets out into the environment, sulphuric acid can acidify rain. Many industries use and make nitric acid for use in nitrate fertilizers and in explosives. The steel industry uses hydrochloric acid to clean metal sheets before processing. On the other side of the pH scale, paper manufacturers make use of sodium hydroxide to remove lignin from paper pulp. Also called lye, food producers use it as a chemical peeling agent for fruits. Bleach also finds use in the production of explosives, and care should be taken in the household, where it can commonly be found.

Perhaps the most common alkaline material found in the average home, sodium bicarbonate is a relatively weak base, weighing in at a pH of 8.3. Also known as baking soda, sodium bicarbonate is commonly used as a cooking ingredient where it acts to lower the temperature at which the browning reaction occurs. Humans also use it in products to soothe stomach acid.

Sodium hydroxide has a pH that sits around 14, the top of the pH scale. Commonly called lye or soda lye, the chemical reacts rapidly in water, causing a rapid rise in temperature that, in some cases, can ignite combustible materials. Because it is so corrosive, it is rare for commercial outlets to sell it in concentrations in water higher than 50 percent. It has some human uses, including the manufacturing of paper, explosives, dyes and soaps. Many household drain and oven cleaners also contain lye.

Humans create ammonium hydroxide by adding ammonia gas to water, which creates a liquid with a high pH and a stark ammonia smell. Highly poisonous and caustic, ammonium hydroxide can kill or seriously injure human beings. Mostly, commercial producers sell this chemical as household ammonia, a common cleaning agent.

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International symbols warn people that the contents of containers are dangerous.  Hazard pictograms alert us to the presence of a hazardous chemical.  The pictograms help us to know that the chemicals we are using might cause harm to people or the environment.  The CLP hazard pictograms are very similar to those used in the old labelling system and appear in the shape of a diamond with a distinctive red border and white background.  One or more pictograms might appear on the labelling of a single chemical.

Hazard symbols have come a long way from the rudimentary drawings used to designate poison in the early 1800s. As a result of updated OSHA chemical labeling requirements, 2016 marks the first full year of adoption of the Globally Harmonized System of Classification and Labeling of Chemicals (GHS) in the U.S.

The GHS system, part of OSHA's Hazard Communication Standard (HCS), consists of nine symbols, or pictograms, providing recognition of the hazards associated with certain substances. Uses of eight of the nine are mandatory in the U.S., the exception being the environmental pictogram. Each pictogram covers a specific type of hazard and is designed to be immediately recognizable to anyone handling hazardous material.  In addition to pictograms, labels are required to include a signal word (“danger” or “warning”), a brief hazard statement and a precautionary statement outlining ways to prevent exposure. 

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An indicator is a substance that changes colour when it comes into contact with something acid or alkali. Several materials occurring in nature will do this, including litmus, which comes from lichen and a substance in red cabbage. By using a range of different dyes, scientists make something called a universal indicator, which is able to show how acidic or alkali a substance is.

Indicator any substance that gives a visible sign, usually by a colour change, of the presence or absence of a threshold concentration of a chemical species, such as an acid or an alkali in a solution. An example is the substance called methyl yellow, which imparts a yellow colour to an alkaline solution. If acid is slowly added, the solution remains yellow until all the alkali has been neutralized, whereupon the colour suddenly changes to red.

Like most indicators, methyl yellow is visible even if its concentration is as low as a few parts per million parts of solution. Used at such low concentrations, indicators do not have any influence on the conditions for which they are recommended. The common application of indicators is the detection of end points of titrations.

The colour of an indicator alters when the acidity or the oxidizing strength of the solution, or the concentration of a certain chemical species, reaches a critical range of values. Indicators are therefore classified as acid-base, oxidation-reduction, or specific-substance indicators, every indicator in each class having a characteristic transition range. Methyl yellow, an acid-base indicator, is yellow if the hydrogen ion (acid) concentration of the solution is less than 0.0001 moles per litre and is red if the concentration exceeds 0.0001. Ferrous 1,10-phenanthroline, an oxidation-reduction indicator, changes from red to pale blue when the oxidation potential of the solution is increased from 1.04 to 1.08 volts; and diphenylcarbazone, an indicator for mercuric ion, changes from yellow to violet when the mercuric ion concentration is increased from 0.000001 to 0.00001 mole per litre. Each of these indicators thus has a relatively narrow transition range, and each is capable of giving a sensitive, sharp indication of the completion of a reaction, that is, the end point.

Although the visible change of the indicator is usually a colour change, in some cases it is a formation or disappearance of turbidity. If, for example, a soluble silver salt is added to a solution of cyanide that contains a trace of iodide, the solution remains clear until all the cyanide has reacted to form the soluble silver cyanide complex ion. Upon the addition of more silver, the solution becomes turbid because insoluble silver iodide forms. Iodide is therefore an indicator for excess silver ion in this reaction.

Another kind of indicator is the adsorption indicator, the best-known representative of which is the dye fluorescein. Fluorescein is used to detect the completion of the reaction of silver ion with chloride ion, the colour change occurring in the following manner. After a quantity of silver large enough to precipitate all the chloride has been added, additional silver ion is partially adsorbed on the surface of the particles of silver chloride. Fluorescein also is adsorbed and, in combining with the adsorbed silver ion, changes from yellow-green to red.

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The abbreviation pH stands for “power of hydrogen”. It describes how concentrated the hydrogen ions in a substance are. A pH value below seven shows that the substance is acid. Above seven, it is an alkali.

The pH value describes the activity of hydrogen ions in aqueous solutions typically on a scale of 0 to 14.  Based on this pH scale, liquids are characterized as being acidic, alkaline or neutral: a solution which is neither acidic nor alkaline is neutral.  This corresponds to a value of 7 on the pH scale.  Acidity indicates a higher activity of hydrogen ions and a pH measurement value lower than 7.  Alkaline solutions are characterized by a lower hydrogen ion activity or higher hydroxide ion activity.

The pH scale is logarithmic.  A difference of one pH measurement unit represents a tenfold, or ten times increase or reduction of hydrogen ion activity in the solution.  This explains how a solution's aggressiveness increases with the distance from the neutral point.

One of the keys to understanding pH measurements is the term "activity", because the activity is temperature dependent it is not the same as the solution's concentration.  Activity, a, is defined as the product of the activity coefficient, y, which is always smaller than 1, and the actual concentration, c, of the concerned compound (a=y * c).

Activity is the effective concentration of a chemical compound, or more precisely its particles in the solution.  In a real solution the activity is constantly smaller than the actual concentration.  This is true because only in an ideal (infinitely thinned) solution the saluted particles do not affect each other.  In this case they are spread apart because many molecules of the solvent are between them.  The difference between activity and concentration becomes apparent in real solutions of ions, because ions interact with each other as a result of their electric charge.  To describe or calculate the characteristics of a solution as exactly as possible the activity and not the concentration must be used in the mass action law.

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A base is the opposite of an acid. Most soap and many household cleaners are bases. An alkali is a base that can be dissolved in water. People commonly use the term alkaline for basic solutions, but their meanings are not the same. All alkaline solutions are basic, but not all bases are alkaline. It's common to refer to the alkalinity of a substance, such as soil, when pH is the property you're really discussing.

In chemistry, a base is a water solution of any chemical compound that produces a solution with a hydrogen ion concentration lower than that of pure water. Sodium hydroxide and ammonia are two examples. Bases are the chemical opposites of acids. Bases reduce the hydrogen ion concentration in water whereas acids increase them. Acids and bases neutralize each other when they combine.

In chemistry, the term alkali refers to salts (ionic compounds) containing alkali and alkaline earth metal elements that accept a hydrogen ion in solution. Alkaline bases are best known as bases that dissolve in water. Alkali metals react vigorously with water, producing hydroxides and releasing hydrogen. The reaction with air covers the surface of the solution with oxides. In nature, ionic compounds (salts) contain alkali metals but never in a pure state.

Alkaline bases include a slimy or soapy feel to the touch because of saponification of fatty acids in human skin. Alkalis form hydroxide ions (OH-) when dissolved in water and all are Arrhenius bases. Normally water-soluble, some alkalis, such as barium carbonate, become soluble only when reacting with an acidic solution containing water. Moderately concentrated solutions (pH of 7.1 or greater) turn litmus paper blue and phenolphthalein from colorless to pink. Concentrated solutions cause chemical burns (caustic).

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The word “acid” comes from a Latin word meaning sour. Acids contain hydrogen and, when dissolved in water, produce positively charged hydrogen ions. Our tongues are able to detect acidic flavours, such as those of vinegar or citrus fruits, but these are very weak in comparison to some acids used in industry, such as sulphuric acid, which burns badly if it comes into contact with skin.

Acids are chemical agents that release hydrogen ions when added to water. Their chemistry makes them one of the most important classes of molecules in nature and science. So many of us have heard of the term pH, which in general is the measure of the amount of acidity or alkalinity that is in a solution. More specifically, it is a measure of the amount of protons or hydrogen ions that are present in an aqueous solution. Acids are primary contributors to the measure of pH in a solution, and the presence of acids a key characteristic of almost all solutions.

The pH scale is a scale that is used to represent the level of acidity in a solution. A solution with a pH of 7 is neutral, while a solution with a pH below 7 is an acid, and a solution with a pH above 7 is a base. An acid dissociates, or breaks apart, and donates protons, or hydrogen ions, in an aqueous solution, while a base donates hydroxide ions in a solution. Water, for example, is neutral with a pH of 7. When acids are added, they release more hydrogen ions into the solution, and this causes the pH of the solution to drop. Let me repeat: more hydrogen ions equals a lower pH and a more acidic solution.

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Poor metals have a low melting point and are quite soft, but they are still very useful. The seven metals that come to the right of the transition metals in the periodic table are known as poor metals. They are aluminium, gallium, indium, thallium, tin, lead and bismuth. Lead has a very high density, so radiation cannot easily pass through it. That is why radioactive materials are often carried in lead-lined containers and the operators of x-ray machines wear lead aprons. Poor metals may be combined with other metals to form useful alloys.

The name aluminum is derived from the ancient name for alum (potassium aluminum sulphate), which was albumen (Latin, meaning bitter salt). Aluminum was the original name given to the element by Humphry Davy but others called it aluminum and that became the accepted name in Europe. However, in the USA the preferred name was aluminum and when the American Chemical Society debated on the issue, in 1925, it decided to stick with aluminum.

Aluminum is a soft and lightweight metal. It has a dull silvery appearance, because of a thin layer of oxidation that forms quickly when it is exposed to air. Aluminum is nontoxic (as the metal) nonmagnetic and non-sparking.

A silvery and ductile member of the poor metal group of elements, aluminum is found primarily as the ore bauxite and is remarkable for its resistance to oxidation (aluminum is actually almost always already oxidized, but is usable in this form unlike most metals), its strength, and its light weight. Aluminum is used in many industries to make millions of different products and is very important to the world economy. Structural components made from aluminum are vital to the aerospace industry and very important in other areas of transportation and building in which light weight, durability, and strength are needed. The use of aluminum exceeds that of any other metal except iron. Pure aluminum easily forms alloys with many elements such as copper, zinc, magnesium, manganese and silicon.

Nearly all modern mirrors are made using a thin reflective coating of aluminum on the back surface of a sheet of float glass. Telescope mirrors are also coated with a thin layer of aluminum. Other applications are electrical transmission lines, and packaging (cans, foil, etc.).

Because of its high conductivity and relatively low price compared to copper, aluminum was introduced for household electrical wiring to a large degree in the US in the 1960s. Unfortunately problems on the functioning were caused by its greater coefficient of thermal expansion and its tendency to creep under steady sustained pressure, both eventually causing loosening the connection; galvanic corrosion increasing the electrical resistance.

The most recent development in aluminum technology is the production of aluminum foam by adding to the molten metal a compound (a metal hybrid), which releases hydrogen gas. The molten aluminum has to be thickened before this is done and this is achieved by adding aluminum oxide or silicon carbide fibers. The result is a solid foam which is used in traffic tunnels and in space shuttle.

Aluminum is an abundant element in Earth's crust: it is believed to be contained in a percentage from 7.5% to 8.1%. Aluminum is very rare in its free form. Aluminum contribute greatly to the properties of soil, where it is present mainly as insoluble aluminum hydroxide.

Aluminum is a reactive metal and it is hard to extract it from its ore, aluminum oxide (Al2O3). Aluminum is among the most difficult metals on earth to refine, the reason is that aluminum is oxidized very rapidly and that its oxide is an extremely stable compound that, unlike rust on iron, does not flake off. The very reason for which aluminum is used in many applications is why it is so hard to produce.

Several gemstones are made of the clear crystal form of aluminum oxide known as corundum. The presence of traces of other metals creates various colors: cobalt creates blues sapphires, and chromium makes red rubies. Both these are now easy and cheap to manufacture artificially. Topaz is aluminum silicate coloured yellow by traces of iron.

Recovery of this metal from scrap (via recycling) has become an important component of the aluminum industry. Industrial production world-wide of new metal is around 20 million tons per year, and a similar amount is recycled. Known reserves of ores are 6 billion tones.