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

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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

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