THE MEASUREMENTS IN CHEMISTRY
In order to understand the quantitative relationships which exist between various kinds of matter, the chemist who is interested in matter and changes which it undergoes, has to measure the quantities of matter with which he works, that is since mass is the measure of the quantity of matter, he is to measure mass. The measuring device the chemist is to employ in this determination should be the balance.
Since for every chemical change there is always accompanying energy change which the chemist has to take into account, the calorimeter and the thermometer have to be used.
The chemist usually employs graduated cylinders, burettes, pipettes and volumetric flasks for the measurements of volumes of liquids, and the gas burette for the measurement of volumes of gases.
The chemist employ the barometer if he has to measure the pressure. The analytical chemist and the physical chemist employ such devices as calorimeters, polarimeters, refractometers and a number of electrical devices.
If the chemist is to examine very small samples of matter, he should use a microscope. The microscope is an instrument which by the combination of lenses permits men to see objects which are too small to be seen with a naked eye; It is an instrument which is useful in many sciences and which, although more frequently used in a qualitative way, can also be used quantitavely.
THE METRIC SYSTEM
The fundamental unit of the metric system is the metre. The millimeter and centimetre are the units which the chemist uses very frequently in his work. If one is to measure extremely short distances, the micron is to be used.
The unit of mass is the gram, milligram or the kilogram.
The unit of the heat measurement is the calorie.
Words to be remembered:
in order to burette
quantitative flask
to undergo volumetric
relationship pressure
device sample
determination unit
balance frequently
№9
ISOTOPES
The word “isotope” is derived from the Greek “isos”, “topos” and means “the same place”.
Hence, isotopes are atoms having the same atomic number, but differing in atomic weight (mass number), e.g. ¹²9C and ¹³6 C are isotopes of carbon, or one out of every 5,000 atoms of hydrogen has an atomic weight of 2.016 instead of 1.008.
This odd atom has a neutron in its nucleus as well as a proton, it being known as heavy hydrogen. The water containing it is known as heavy water.
Isotopes occur with considerably greater frequency in other elements than in hydrogen, an extreme case being chlorine, its atomic weight being 35.5. It is made up of two groups of atoms in a ratio of 3:1, the weight of one group being 35, that of the other 37.
In the case of uranium, for example, one isotope of atomic weight 235 is found in every 140 atoms of the standard weight, with the weight being 238.
The chemical properties of isotopes being identical with those of regular atoms, their discovery was of little interest to chemists. Physicists, however, got interested in them, a new way of approaching to the structure of matter being opened.
Words to be remembered:
nucleus chlorine
as well as ratio
contain identical
considerably approach
extreme case
Notes on the text:
odd atom - лишний атом
in the case of uranium - если мы имеем дело с ураном (в случае с ураном) regular atoms - обычные атомы
e.g. = for example - например
№10
LIQUIDS (I)
The liquid state occupies an intermediate position between the gaseous and solid states, liquid having a definite volume but no definite shape.
Like a gas, a liquid can take the shape of any vessel in which it is put, but in contrast to a gas, a definite quantity of liquid is required for filling the vessel. A liquid cannot be compressed so much as a gas because its molecules are already close together, large pressure producing small changes in volume.
Increasing the temperature increases the kinetic energy of all molecules.
The change of a liquid into a gaseous or liquid states being dependent upon the kinetic energy of the molecules, which in turn is dependent upon the temperature, there are definite temperature characteristics for most liquids at which these changes occur. They are known as transition temperatures.
If we place one liquid layer carefully on top of a layer of a more dense liquid in which it is soluble, and set the vessel where it won’t be disturbed, we shall see that two liquids begin gradually mixing. It is also to be taken into consideration that all liquids do not flow with the same ease, water, alcohol, gasoline flowing easily, while heavy oil glycerin flowing very slowly.
When a liquid flows, layers of molecules begin rubbing over each other, friction being generated by this rubbing of layers of particles. The greater the friction, the slower is the flow. A liquid which resists flowing, or resists the reaction of any other deforming force upon it results in a homogeneous solution. We give this example for illustration that the molecules of a liquid diffuse, though much slowly than do those of a gas.
The molecules of a liquid are much closer together than they are in a gas, because of the greater relative strength of attraction, the density of liquids being much greater. Naturally as the volume of a liquid begins varying with temperature its density will also start varying with temperature.
It should be noted that the closeness of the molecules also is known as viscous, the opposite of viscosity being fluidity. Viscosity diminishes and fluidity increases with temperature.
Words to be remembered:
intermediate soluble
shape gradually
vessel to flow
to compress gasoline
to increase rub
dependent friction
transition viscosity
layer fluidity
dense in turn
№11
LIQUIDS (II)
The molecules within the interior of a liquid have a definite average energy of motion, and thus a definite average velocity at each temperature. Some of them, however, at any given instant, have a velocity sufficiently greater than the average velocity to enable them to break through the surface layer of molecules and escape. Thereafter they are free to wander about in the space above and constitute a vapour - namely a gas that can be condensed to a liquid merely by increasing the pressure upon it. (Air is not a vapour, for to condense it to a liquid it must be both compressed and cooled).
The escape of the molecules from a liquid into its vapour is called evaporation. After a sufficient number of molecules have collected in the space above the liquid, their haphazard wanderings bring them back to the surface as fast as other molecules escape. Thereafter, there is a balance between evaporation and recondensation and thus a constant number of molecules within the closed space at any given moment; and these, by bombardment of the walls of the vessel set up a constant pressure, called the vapour pressure.
Words to be remembered:
interior volatile
average to escape
motion constant
sufficient within
surface velocity
vapour thereafter
evaporation wander
№12
SOLID STATE (I)
If you take a paper clip and bend it would stay bent, it wouldn't, spring back and it wouldn’t break. The metal of which the clip is made is ductile. Some other materials are not ductile at all. If you tried to bend a glass rod (unless you are holding it in a flame), it would simply break. It is brittle. In this respect as in many others, glass behaves quite differently from a metal. The difference must lie either in the particular atoms of which metals and glass are made up or in the way the are put together, probably both. There are of course many other differences between metals and glass.
Metals, for example, conduct electricity and therefore are used for electrical transmission lines, glass hardly conducts electricity at all and can serve as an insulator. Glass being transparent, it can be used in windows whereas a sheet of metal even more than a millionth of an inch thick is quite opaque. It is of course interesting to understand the reasons of these differences in behaviour.
During the past 20 years studies of this kind have been called solid-state physics, or sometimes since the subject includes a great deal of chemistry, just “solid state”. It is a major branch of science that has revealed new and previously unsuspected properties in metals. Solid-state physics has become one of the most important branches of technology. It has given rise to technological progress. Having studied this branch of technology, engineers could understand much better the phenomenon of quantum mechanics as it is applied to solids. Though solids, of course, were the subject of experimental investigation long before quantum mechanics was invented.
Words to be remembered:
interior therefore
opaque transparent
ductile branch
break conduct
insulator previously
№13
SOLID STATE (II)
If we consider the fact known since the earliest studies of electric currents, we should remember that metals conduct electricity well and most materials do not.
It is only the discovery of electron that could help the scientists to understand some of these facts well. With the discovery of electron it was assumed that in metals some or all of the atoms had lost an electron and that in insulators such as glass they had not. The electrons in a metal proved thus to move freely, whereas the electrons in insulators do not. Why did this happen in metals? This very question had to await the discovery of quantum mechanics. The next question was: “How are the electrons arranged?”
As far as this question is concerned we can say that solids can be divided into two classes: crystalline and amorphous. In the crystalline group, which is the largest and includes the metals and most minerals, the atoms are arranged in a regular way. In some metals (for instance copper and nickel) they are backed together. In other metals (such as iron, for example), they are arranged in the form of a cube. The commonest of the amorphous group of solids appear in glass, its atoms are put together in a more disordered way than those of a metal.
The structure of an amorphous material is much more difficult to discover than that of a crystalline solid and considerable effort is being made to learn more about the arrangement of atoms in such materials.
Much has been learned about solids but much is still to be learned. There is a number of problems which are to be solved. No wonder that many scientists have been working at this interesting, so-called “solid state” science.
Words to be remembered:
to consider copper
electric current considerable
discovery effort
to arrange to appear
for instance to solve
№14
PROPERTIES OF SOLIDS
The molecules of solids are close to each other, they are vibrating in a fixed position. There is a strong force of attraction between molecules in a solid. Because of the strong attraction between molecules solids have certain properties. If we examined solids thoroughly, we should find that these properties are: tenacity, hardness, malleability and ductility.
Tenacity is a measure of solid’s resistance to being pulled apart. Steel has a high tensile strengths concrete has a much lower tensile strength. Hardness is a measure of a substance’s ability to scratch another substance. The diamond is the hardest solid, it being able to scratch all other substances.
Malleability refers to a solid’s ability to be hammered or rolled into thin sheets. Gold is famous for its malleability, copper, tin and aluminum being other examples of malleable materials.
Ductility is the ability to be drawn out in the form of wires.
Notes on the texts:
tenacity - вязкость to scratch - царапать
malleability - ковкость to draw our - извлекать
ductility - пластичности wire - провод
Words to be remembered:
attraction tensile
certain concrete
hardness strength
resistance ability
tensile diamond
№15
ORGANIC CHEMISTRY
Organic chemistry is an extremely interesting field of natural science and of great technological significance. The overwhelming majority of chemists prove to be engaged in producing organic compounds, several millions being known so far.
In view of their obvious success in the manufacture of synthetic compounds, the chemists are greatly interested in this field of science.
The name organic chemistry, which was originally used to refer to the chemistry of substances that occur in living organisms, is now used for the chemistry of the compounds of carbon. The chemistry of carbon was greatly influenced about a century age through the development of a general structure theory, this theory being a chemical theory, induced from chemical facts.
In recent years it has received added verification through the determination of exact structures of molecules and crystals by physical methods, especially X-ray diffraction, electron diffraction, and the analysis of the spectra of substances.
During the first half of the 19th century many organic compounds were found, to have been obtained from plants and animals and also to have been made in the laboratory. They were analyzed for their constituent elements and their properties were carefully studied. Efforts were made to find some correlation between the chemical composition and the properties of the substances.
Word to be remembered:
significance determination
majority occur
manufacture exact
verification so far
through constituent
№16
ELEMENTARY CARBON
Carbon occurs in nature in its elementary state in two allotropic forms namely diamond, this being the hardest substance known, and graphite, a soft, black crystalline substance used as a lubricant. Having investigated all the substances thoroughly the scientists found charcoal, coke, and carbon black to be microcrystalline or amorphous (non-crystalline) forms of carbon.
Carbon burns to form gases: carbon monoxide CO, and carbon dioxide CO2, the former being produced when there is a deficiency of oxygen or the flame temperature is very high.
This investigation followed by others resulted in new discoveries in the field of carbon. It has been found out that carbon monoxide is a colourless, odourless gas with small solubility in water. It is poisonous, because of its ability to combine the hemoglobin in the blood in the same way that oxygen does, and thus to prevent the hemoglobin from combining with oxygen in the lungs and carrying it to the tissues. It should be noted that the exhaust gas from automobile engines contain some carbon. Nevertheless carbon monoxide is a valuable industrial gas, for use as a fuel and as a reducing agent.
Words to be remembered:
diamond flame
soft odour
lubricant solubility
thoroughly blood
to burn tissue
deficiency fuel
Notes on the texts:
charcoal – древесный уголь amorphous – аморфный, некристаллический
allotropic – аллотропный because of – из-за
№17
CARBON DIOXIDE
Carbon dioxide is a colourless, odourless gas with a weakly acid taste, due to the formation of some carbonic acid when it is dissolved in water. It appears to be about 50% heavier than air. It is easily soluble in water, one liter of water at 0°C dissolving 1,713 ml of gas under 1 atm pressure.
When crystalline carbon dioxide is heated from a very low temperature its vapour pressure reaches 1 atm at 79° at which temperature it vaporizes without melting. If pressure were increased to 2,5 atm the crystalline substance could be changed directly to a gas.
Carbon dioxide is known to combine with water to form carbonic acid H2CO3, it being a weak acid.
If you studied all the properties more thoroughly you would see that carbon dioxide is used for the manufacture of sodium carbonate, sodium hydrogen carbonate, and carbonated water and for many other uses.
From this short review it’s clear that chemistry of carbon and its compounds is a very important field of chemistry and should be studied carefully.
Words to be remembered:
colourless to vaporize
odourless to increase
acid to combine
taste weak
due to sodium
to dissolve review
soluable carefully
№18
FUEL
Carbon and hydrogen are the principal constituents of the solid fuels coal and wood. Coal has been formed in nature by the slow decomposition of vegetable matter, in the presence of water and absence of air. Most of it was formed during the Carboniferous Period of geologic time, about 250 million years ago. Coal consists of free carbon mixed with various carbon compounds and some mineral matter. Anthracite coal (hard coal) contains much volatile matter, and burns with a smoky flame.
Bituminous coal can be converted into coke by heating without access of air. When the heating is carried out in a by-product coke oven, many substances distill out, including gas for fuel, ammonia and a complex mixture of liquid and solid organic compounds. The solid material remaining in the ovens, consisting mainly of carbon, is called coke. It burns with a nearly colorless flame, and is used in great amounts in metallurgical processes.
Petroleum is a very important liquid fuel. It is a complex mixture of compounds of carbon and hydrogen.
The gas obtained from a coke furnace (coal gas) consists of hydrogen (about 50%), methane CH4 (30%), carbon monoxide (10%) and minor components. This coal gas was the original illuminating gas.
Natural gas, from gas wells and all wells, consists largely of methane.
Words to be remembered:
hydrogen mixture
principal petroleum
decomposition furnace
vegetable to consist
presence to remain
absence gas well
volatile oil well
access compound
№ 19
HYDROGEN
Hydrogen is known to be the lightest of the elements. If the temperature is 20°С, it is a colourless, odourless, tasteless gas, its density being 0,08987, i.e. 1/15 that of air.
Hydrogen was liquefied. The device used for it proved to be similar to that used in liquefying air. The gas is only slightly soluble in water, its solubility under standard pressure in 100 ml of water being 1,93 ml at 0°C.
Hydrogen could be found in the free state only in minute quantities because of its marked chemical activity. It is known to be prepared in the laboratory by its liberation from acids, bases, or water.
Specialists consider hydrogen to be an extremely promising energy source. The reserves of hydrogen are known to be practically unlimited, it containing almost three times more thermal energy than benzene. Another plus is that hydrogen can be used as fuel in transport, industry and at home.
Extensive use of hydrogen as an energy source will help to keep the environment clean - hydrogen combustion produces simply the vapour of distilled water.
Hydrogen is easy to transport and store. It could be shipped over large distances using conventional pipelines.
Even today it costs several times less to transport by pipe-lines than to transmit electricity across huge power lines, bike any other gaseous fuel it could be accumulated and kept for a long time either in conventional or natural reservoirs.
Scientists have found many ways of producing hydrogen on a commercial scale - basically from ordinary water. Large volumes of this fuel could be obtained from coal, its reserves being tremendous.
Words to be remembered):
tasteless liberation
density source
to liquefy environment
device combustion
similar pipe-line
soluble tremendous
quantity ordinary