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Organic chemistry is the study of compounds containing carbon. It is called «organic» because scientists used to think that these compounds were found only in living things or fossils. However, vast numbers of different carbon-containing compounds can now be produced artificially in laboratories and factories, for use in industry. For example, drugs, plastics, and pesticides are all synthetic organic substances. About 4. 5 million of the 5 million compounds known today contain carbon.

Text 2 

An important nonmetallic element, carbon occurs naturally in three forms, or allotropes. There are graphite, diamond and buckminster-fullerence. Carbon can form millions of different compounds (combinations of elements). This is because a carbon atom can bond with up to four atoms (of carbon or other elements) and because the carbon atoms can link up in chains and rings of different sizes and patterns.

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Organic (carbon-containing) compounds can be divided into two major groups – aliphatic and aromatic compounds – according to the way in which the carbon atoms bond. In aliphatic compounds, the carbon atoms are linked in chains. These chains can contain anything from two to many thousands of carbon atoms, with other types of atoms attached to each carbon atom. In aromatic compounds, the carbon atoms are joined in a ring.

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Acids are substances that release hydrogen ions in water. Alkalis are substances that release hydroxide ions (ions made up of hydrogen and oxygen) in water. If acids and alkalis are mixed, the two types of ions cancel each other out, and a new substance called a chemical salt is formed. The acidity or alkalinity of a substance can be measured using the pH (potential for hydrogen) scale, which runs from 1 to 14. All acids have a pH lower than 7; the stronger the acid, the lower the pH. All alkalis have a pH greater than 7; the stronger the alkali, the higher the ph. Neutral substances, such as water, is neither acidic nor alkaline. They have a pH of 7.

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The Earth provides all the raw materials we need. The problem is to separate the substances we want from the mixtures in which they naturally exist. Chemists use a variety of different methods of separation, depending on the type of mixture and the properties of the substances it contains. We sometimes need to separate substances at home, too. In a coffee-maker, for example, a filter separates the ground coffee beans from the liquid coffee. This is known as filtration.

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Separating the different parts of a compound using electricity is called electrolysis. For this to work, the compound must be either in molten form or dissolved in water, and it must contain ions. Two electricity – conducting plates (called electrodes) are placed in the compound to be split (called the electrolyte). When the plates are connected to a battery, an electric current passes through the compound, which is gradually split into two parts. This happens because the negative electrode (the cathode) has an excess of negatively charged particles, so it attracts the positive ions of the compound. The positive electrode (the anode) attracts the negative ions.

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A chemical reaction occurs when substances change into new substances. For this to happen, the bonds between atoms and molecules must break and re-form in different ways. Because the bonds can be strong, energy, usually in the form of heat, is often needed to start a reaction. The new substances (products) have properties different from those of the original substances (reactants). Chemical reactions do not occur only in laboratories; they happen all around us – for example, when cars rust and when food is cooked.

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A solution forms when one substance (usually a solid) dissolves in another (usually a liquid). The solid (called the solute) breaks up into tiny particles and spreads throughout the liquid (the solvent) so that you can no longer see any solid. Solutions are always clear; if the mixture is cloudy, it is a suspension. Solid particles spread throughout the liquid, but the particles are bigger than those of a solution. If you leave a suspension to stand, most of the solid particles will eventually sink. A solution will not separate out in this way.

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At room temperatures, water is a clear tasteless and odorless liquid. It is made up of hydrogen and oxygen atoms grouped together as molecules. The molecules draw together at the surface of water to form surface tension, which acts like a kind of skin. They are also drawn to the molecules of other substances, which is why water «wets» things, like drinking glasses, or our bodies when we swim.