Tiêu đề: Anh văn chuyên ngành Hóa ( tài liệu cùa Cô Hà ) Fri Mar 19, 2010 5:28 pm
Unit 1 : LIGHT Light travels very fast. It moves at 186.300 miles a second; that is 300.000 kilometers a second. Light reaches us from the moon in less than a second and a half. The moon is about 238.800 miles from us; it is more than 380.000 kilometers away. Light from the sun reaches us in 8.1/2 minutes. The sun is about 93 million miles from the earth. The stars are farther away than the sun. Light from the nearest star reaches us about four years. When you look at the star, you do not see its present conditions. You see it as it used to be. Light from some stars takes hundreds of the years to reach it. We never see a star as it is now. We see it as it was long ago: perhaps hundred or thousand of years ago. Astronomers watch the stars through big telescopes. Some of these telescopes have glass lenses in them. A lens is around piece of glass. But it is not flat. The side of lens is curved. The middle part of some lenses is thicker than the edge. In order lenses, the edge is thicker than the middle part. Cameras have lenses at the front. A very good lens costs a lot of money; it costs more than any other part of the camera. A ray of light usually travels in a straight line; but sometimes it bends. The light reaches the film of camera through the lens. It leaves the air and goes in to the glass. Then it bends. The ray also bends when it leaves the glass. Light also bends when it reaches the lenses of a telescope. Some telescopes do not use a lens at the front. They use a curved mirror at the back. A curve mirror is better than a lens in some ways. The world’s biggest telescopes are on Mount Palomar in America. Near it, on Mount Wilson, there is another big telescope. Both of them use mirror, not lenses at the front. With these great telescopes astronomers can see star and the other things very far away. Some of these things are not only stars. They are great groups of stars. The earth is in a group of stars. There are about 100.000.000.000 stars in it. We call this group the galaxy. Outside the galaxy there is empty space; but thousands of millions of miles away there is another galaxy. Light from this other galaxy reaches us after about 2 million years. There are millions of these galaxies; and they appear to be the rushing away from us. The astronomers at Mount Palomar and Mount Wilson can see some of them well; but they cannot see one as it is now. The light takes millions of years to arrive; so they see a distant galaxy as it used to be. The light left it millions of years ago. It traveled across space and then went in to an astronomer’s eye. Perhaps no men were living when they started.
Unit 2 : SUBSTANCES AND THEIR TRANSFORMATIONS All objects surrounding us in nature are composed of different substances. Iron, glass, wood, water, sugar, etc…Are all examples of such substances? Chemistry is the study of substances and their transformations. Therefore, the first problem we take up upon beginning a course in chemistry is how to distinguish and recognize substances. Substances are distinguished by their properties – color, taste, specific gravity, greater or less hardness, melting and boiling points, etc. For example, in describing the properties of sugar, we can taste that sugar is a hard, brittle substance, white in color, sweet in taste, without odor, easily soluble in water, heavier than water, with a specific gravity of 15.8, etc. In order to learn the properties of a substance one must have it in its pure form. Even small admixtures of foreign substances may change properties of substance. For example, pure water is colorless, tasteless and transparent, but if drop milk is added to a glass of water, water becomes clouded; if a drop of ink is added, the water becomes colored. All the enumerated properties are not those of water, but of the admixtures. In some case we may see at once that a substances in heterogeneous that is a mixture of different substances. Take granite, for example. We notice in its pink particles of field-spar, semitransparent crystals of quartz and dark shining scales of mica. In other case it can not be seen at a glance that a given substances is heterogeneous, but this may be detected by various methods. Thus the heterogeneity of milk may be shown if we let the milk stand: the thicker layer of cream rises to the top. This means that milk is heterogeneous. We can also use a microscope. Under the microscope it will be clearly seen what milk is a liquid which consists of tiny suspended globules of fat.
Unit 3 : PHYSICAL CHANGE AND CHEMICAL CHANGE In experiments with different objects, two sorts of change can be produced. An iron, for example, can be heated, cooled, bent, cut or magnetized. Expect for the cutting, the changes are easily reversed. More important, the iron is still iron. Such changes are called physical changes. In physical change, substances are altered their properties but they are not changed to different substances. Melted wax is still a wax and frozen water (even though we give it a difference name, ice) is still composed of water. Nearly all substances are solids at low temperatures, gaseous at high temperatures and liquid at some intermediate range of temperatures (iodine at ordinary pressure is an exception since it does not from a liquid). Further more, melting and boiling are easily by cooling the substance instead of heating it. Ready reversal is relatively common among physical changes. In another sort of change, call a chemical change, the original substances disappear and new substances are formed. When iron rusts, the metal disappear and a new substance, a brown powder or scaled call rust, is formed. Rust is not iron but it contains iron. The change form iron to rust is not at all easy to reverse. The iron and steel we use are made from hematite, a brown rock similar in composition to rust, but fierce heating with coke is needed to accomplish the change. Another chemical change occurs if we place a nail in a glass beaker and pour beaker and pour over it an acid such as hydrochloric acid. Bubbles of gas escape and the nail disappear in solution. If we heat the acid in which the nail dissolved, water and acid are driven off and we eventually recover yellow crystals quite unlike the original iron nail. On the other hand, if we and some common salt to water and stir, the salt disappears but on driving the water off by heating we can recover the salt unchanged. We concluded that when the salt dissolved, it became distributed through the water without changing into another substance. The change in dissolving salt in water is therefore a physical change but dissolving the nail in acid is a chemical change. Both physical and chemical change is accompanied by change in energy, commonly by the taking in or giving out of heat. Thus boiling requires to be supplied and condensation, the reverse process, gives out heat. Large heat effects are particularly common in chemical changes and the production of much heat is often an indication that a chemical changes is taking place. A physical change occurs when a substance is changed in from or properties but is not changed into other substance. A chemical change occurs when a substance is changed into one or more other substance.
Unit 4 : PROPERTIES OF SOLOIDS Solids which, like butter, can be easily altered in shape are sometimes called plastic solids. A brittle solid, like ice, is one which may break if tapped sharply. Knives, scissors and chisels, are brittle and break if one attempts to bend them. A tough solid is likely to bend without breaking. Steels for screw-drivers, spanners and hammers are tough and will usually bend before breaking. Crystals are an interesting form of solid matter. Larger crystals are not common except in laboratories but most solids tend to form crystals. Metals, for examples, are generally crystalline in form although the crystals structure can usually only be seen in specially prepared specimens with the aid of microscope ( the mottle effect of new galvanized iron is due to zinc crystals on the iron sheet). Crystals occur in nature in many rocks. In granite, for example, the crystals are easily visible. Crystals are generally brittle and, when broken, form smaller crystals having the same geometrical shape as the large. The shape of crystals is characteristic for a particular compound. There are flat surface called cleavage planes at definite angles to each other. In a crystal, the atoms or molecules are arranged in a definite pattern, called crystals lattice. When a crystal is forming, e.g. form molten rock, the particles tend to arrange themselves in the crystal lattice. The extent of growth of a crystal depends on a number of factors, one being the time avaible for the crystal growth to occur. In general, the longer the time during which the crystal form the bigger it is likely to be. A solid which does not have a regular arrangement of atoms or molecules within it is said to be amorphous. Super cooled liquid, such as glass and toffee, are examples of amorphous solids. They are said to be supper cooled because they are cooled before the particles have had time to arrange themselves into crystalline patterns. Old glass of some types is sometime s said to be ‘devitrified’. It loses its transparency because the particles have, over a long time, partly arranged themselves into crystals. The glass becomes weak and has to be replaced.
Unit 5: CHANGES OF STATE Molecules in a solid are help together firmly, although they can vibrate about their positions in the solid. Addition of heat energy causes the vibration to become more violent and, at a certain stage, the molecules, although still close enough to attract one another, begin to move independently. Thus there is change of state from solid to liquid, called melting. The change occurs at a particular temperature, called the melting point of the solid. Different solids have different melting points. When the liquid formed by the heated solid is allowed to cool, the motion of the molecules becomes less. As it cools past the melting point, the liquid changes back to the solid. It is said to have solidified or frozen ( ‘frozen’ usually refers to water ). Addition of heat energy to a liquid causes the molecules to move rapidly and a point ( the boiling point of liquid ) is reached where they move so rapidly that at least some become gaseous. The change of state from liquid to gas is call vaporization or boiling. If heat energy is removed from the gas, the molecules lose energy and reach a condition where they return from the gas to the liquid state. The gas is then said to condense. In a liquid, some molecules near the surface possess enough energy to move away from the attraction of nearly molecules and they escape into the gas above the liquid surface. In this way the liquid may slowly become a gas at a temperature below its boiling point. The liquid is thus said to evaporate. When heated, most solid melt to become liquids and the liquids, on further heating, become gases. Some solids, however, when heated pass directly from the solid to the gaseous state. Dry ice, solidified carbon dioxide used for keeping ice cream cold, is one such solid. Iodine is another, such solid are said to sublime.
Được sửa bởi wildfox007 ngày Fri Mar 19, 2010 5:34 pm; sửa lần 1.
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Tiêu đề: Re: Anh văn chuyên ngành Hóa ( tài liệu cùa Cô Hà ) Fri Mar 19, 2010 5:29 pm
Tổng số bài gửi : 147 Được cảm ơn : 104 Birthday : 16/01/1990 Join date : 10/03/2010 Age : 28 Đến từ : Dĩ An - Bình Dương
Tiêu đề: Re: Anh văn chuyên ngành Hóa ( tài liệu cùa Cô Hà ) Sun May 09, 2010 12:17 pm
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Tiêu đề: Re: Anh văn chuyên ngành Hóa ( tài liệu cùa Cô Hà ) Wed May 12, 2010 9:35 pm
Part 2 Unit 6 : TYPE OF SOLUTIONS When substances are mixed together, two general classifications of such mixtures arise: heterogeneous mixtures and homogeneous mixtures. The heterogeneous mixtures can be seen to contain two or more components that are not uniformly distributed within one another. A random collection of iron nails and sugar crystals and pile of sand and the water are heterogeneous mixtures. Most heterogeneous mixtures are a little value to man since pure substances are easier to handle and control. In certain special cases, the heterogeneous mixtures are essential to civilization. A few examples are concrete, whole raw milk and rain. Heterogeneous mixtures usually vary in composition and consistency. In science, we prefer uniform systems of mixtures so that we can have better control and understanding. Therefore, the homogeneous mixture of components is best suited to our needs. The homogeneous mixture is really a uniform solution of material dissolved in one another, such that all parts of the solution are identical not only in physical appearance, but also in composition. We can speak of different kinds of solution – the word solution implies a homogeneous solution. There is a gas dissolved in a gas, such an air. Gases may be mixed in any proportions whatsoever. Another solution would be a gas dissolved in a liquid, such a beer. (CO2, H2O, and ethyl alcohol). Or we could have a solid in a solid such as a sliver coinage (Cu 10%, Ag 90%). As important and useful as above solution may be, they are not as important in chemistry as the solid dissolved in a liquid and the liquid dissolved in a liquid. Examples of these would be salt water (Nail solid and H2O liquid) or vodka (H2O and ethyl alcohol liquid). In both cases, all parts of the homogeneous solution are consistent in physical appearance and composition. The important difference between a pure substance and a homogeneous solution that looks like a pure substance is that the solution may contain different concentrations of materials that can always be isolated in the pure form. For examples, we could dissolve 10g of sugar in 100ml of water or 20g of sugar in 100ml of water, or an infinite variety of other combinations and still end up with a homogeneous solution. It is not itself a pure substances but it is composed of pure substances that may be regained and separated by physical means such as evaporation, fractional distillation (converting the liquid to gas and leaving the solid or less volatile liquid behind), and any other process that would accomplish the desired separation.
Unit 7: POLYMERS Among the major fields of science and technology which are to receive attention in the coming years in chemistry, special attention being paid to the chemistry of polymers and synthetic fibers. The attraction of this field is that substances which never existed on earth, but without which technical progress is impossible, are created. Natural substances can not be like polymers in lightness, strength, chemical durability, ability to absorb and reflect vibrations, stop or let through sound or radio waves or nuclear radiation. Polymers can be porous and monolithic, transparent or opaque. They have long been used as excellent electrical insulators. Now we have produced semi-conductor polymer. Add to this the fact that polymers lend themselves to machining much better than wood, stone or metal and you will understand why so much attention is being given to this man-made material. Some scientist are working to alter the properties polymers obtained from oil and coal resins, the usual raw materials. The quality of polymer depends not only on the components of its giant molecule, but on its structure as well. Another important factor affecting the properties, appearance and quality of a substance is the arrangement of the molecules. Just as the same kind of building material can be used to build either a skyscraper or cottage, the same molecule can be used to create substance with the most varied properties. In order to produce a material with planned properties, the molecules of the required polymers must be placed in a certain order. Still another important factor is the nature of the elementary links which make up a polymer molecule. A method of producing an entirely new group of polymers possessing interesting magnetic properties has been discovered. It is based on the ability of X-Rays and nuclear radiation to destroy the bonds between the atoms of a polymer. This method can be an endless number of hybrids with planned properties.
Unit 8: FRONTIERS OF CHEMISTRY Organic chemistry is a young science. In the 19th century chemist first synthesized, or put together, an organic compound from inorganic (non-organic) material. Further they show that carbon atoms have four available bonds which allow the to combine with other atoms. Since those early years, the organic chemist invented many technique for analyzing compound whose structure are unknown and for preparing compound that do not exist in nature. Many of these compound are now used as medicine, dyed, foods and other products of industry. In the last few decades chemist learn a great deal about the way in which the properties of a molecule are related to its structure. With the help of this knowledge they made great studies in understanding the structure of giant molecules. Another striking development is the increased use of catalysts in both industrial and laboratory processes. Since no one yet knows precisely how catalysts works, each one has to be found by trial and error. Eventually we shall have such tailor made catalysts for we have already known quite a lot about the action of the existing ones. The most difficult problems in organic chemistry are those connected with investigating the compound in living things. Although our knowledge is slight, it is growing rapidly. Think for a moment of photosynthesis, the process by which water and carbon dioxide combine in a green plant to form sugar, although every single person depends on photosynthesis for his food supply, we still do not understand one the reaction. When photosynthesis can be carried out artificially on a large scale, we shall be able to set up factories to mass produce food.
Unit 9: SOLIDS, LIQUIDS AND GASES
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Tiêu đề: Re: Anh văn chuyên ngành Hóa ( tài liệu cùa Cô Hà ) Wed May 12, 2010 9:37 pm
tài liệu của Thầy Hải thì khi nào học thầy sẽ đưa... còn một bài nữa... hehe học tốt môn này nha mấy mems