Tools and measurements in chemistry

Read the text and tell about the tools you really use and measurements you carry out during your laboratory classes.

The experimental chemistry as well as the chemical industry needs instruments for accurate measuring. Good measuring instruments are able to give rapid results. The results had often to be checked thoroughly. There are many different kinds of measuring instruments and there is much information about the instruments which are to be used in chemical plants. The purpose of all measuring devices is to control a chemical reaction.

In order to understand the quantitative relationships which exist between various kinds of matter the chemist 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. Some balances are much more sensitive than others, that is, some can detect smaller differences in mass than others. The analytical balance is the most sensitive as well as electronic one which is used by most of chemists nowadays.

Very often a chemist has to measure volumes of liquids. The commonest instrument is the graduated cylinder. On the side of it one can see scratches. They correspond to milliliters. The cylinder has a lip so that its contents may be poured easily into another container.

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 volumetric flask is used for the preparation of solutions.

The burette and the pipette are used in quantitative analysis and other quantitative work. The burette is a glass tube opened at the top end. The pipette has a scratch on the neck. This scratch is the mark to which it can be filled.

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.

Chemist employ the barometer if they have 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 a chemist is to examine very small samples of matter, he should use microscope. It is an instrument which is useful in many sciences and which, although more frequently used in a qualitative way, can also be used quantitatively.

Notes to the text:

to take into account – принимать во внимание, учитывать

in order to – для того чтобы, чтобы

11. Open the brackets choosing the suitable word. Translate the sentences into Russian:

1. (A balance, a calorimeter, a thermometer) is a device which determines the quantity, but not the quality of heat in a body. 2. If a chemist determines mass, he is to employ (a flask, a thermometer, a balance). 3. (A calorimeter, a flask, a microscope) is used if a chemist must examine small samples of matter. 4. For the measurement of volumes of gases a chem­ist uses (burettes, pipettes, gas burettes). 5. The unit of (volume, mass) in the metric system is the gram. 6. On (the Centigrade scale, the Fahrenheit scale) the freezing point of water is 0°. 7. If a chemist must measure extremely short distances, (the centimetre, the micron) is to be used.

12. Explain what are the following tools and devices used for:

spectrometer, spectrograph, viscometer, polarimeter, barometer, hydrometer, calorimeter, colorimeter, diameter, elastometer, electrometer, galvanometer, manometer, manograph, tautomer, voltmeter, volumeter.

13. Read these words and word-combinations correctly:

liter, milliliter, meter, millimeter, gram, milligram, cubic, cubic centimeter, micron, ounce, pint, pound, inch, yard, per cent, 20 per cent by volume, degree, four degrees Centigrade, 32 degrees Fahrenheit.

Дата добавления: 2014-11-07