2020-05-21
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1) In what state is chlorine found in nature?
2) At what temperature does chlorine liquefy?
3) Is chlorine easily soluble in water?
4) What action does chlorine exert in water?
5) What is the reactivity of chlorine?
6) What products are obtained when sodium chloride or potassium chloride solutions are subjected to electrolysis?
7) By what method is chlorine generally produced?
8) What products are produced if fused sodium chloride is used?
II. Make up a description of any element you like.
Unit 6. ANALYTICAL CHEMISTRY
METHODS OF ANALYSIS
The analysis of a complex material usually involves four steps, sampling, dissolving the sample, separating mutually interfering substances, and determining the constituents of interest. The first step, sampling can be a significant problem, particularly in industrial applications.
Sampling is complete when the subdivision is small enough to permit analysis.
The second step is the dissolving of a sample. If we know the nature of the sample we use a suitable reagent.
Gravimetric methods involve a weighing operation as the final measurement.
Gravimetric analysis have been developed for almost everything from A(luminium) to Z(irconium).
Gravimetric procedures may be done in various ways: by precipitating, by dissolving, by removing as a volatile compound.
Volumetric methods involve measurement of that volume of a solution of known concentration which reacts with a known amount of the sample. Such a solution is called a standard solution.
Volumetric techniques are now applicable to most of the elements and to many specific inorganic and organic compounds. They are widely used in all phases of chemistry, in medicine, and in many allied sciences.
Physico-chemical methods depend upon the measurement of physical properties other than mass and volume. Such methods are important when the simpler methods of analysis are inadequate.
METHODS OF SEPARATION
Methods of separating a solid and a liquid are built around two processes, filtration and centrifugation.
Filtration is the process of passing the suspension of solid and liquified through a porous barrier which will trap the solid. The barrier may be filter paper, sintered glass, asbestos matting, glass wool and others.
Centrifugation is mechanized setting (or floating) and depends upon the difference between the densities of the solid and the solution. Gravitational setting is usually inadequate. A centrifuge can be used to enhance the gravitational force moving the particles. Most centrifuges operate at hundreds of revolutions per minute. Extremely difficult separations require speeds of tens of thousands of revolutions per minute.
NOTES AND COMMENTARY
| are built around two processes – базируются на двух процессах the process of passing … through – прцесс пропускания … через | mechanized setting - механическое осаждение depends upon – зависит revolutions per minute – обороты в минуту |
ION EXCHANGE METHODS IN ANALYTICAL CHEMISTRY
Ion exchange is now one of the recognized processes of chemical engineering. It has been applied to the separation processes of quantitative analysis.
General Principles. By ion exchange we mean the exchange of ions of like sign between a solution and a solid insoluble body in contact with it. For such an exchange to be possible, the solid must contain ions of its own. The solid (called the ion exchanger) must have an open, permeable molecular structure, so that ions and solvent molecules can move freely in and out. Many substances, both natural and artificial, have ion exchanging properties.
In analytical work we are primarily interested in the synthetic organic exchangers. These have a high capacity for holding ions and they are not broken down by acids or alkalies, they have a relatively simple composition.
NOTES AND COMMENTARY
| by "ion exchange" we mean -под ионным обменом мы подразумеваем of like sign -одноименные по знаку for such exchange to be possible –чтобы осуществить этот обмен | of it own -свои собственные can move freely in and out -могут свободно входить и выходить |
CHROMATOGRAPHY AND ION EXCHANGE TECHNIQUE
Chromatography is a method of chemical analysis based upon the selective absorption and partial fractionation of various substances by certain suitable materials. The method is simple and requires a minimum of special equipment. The technique consists of pouring a solution through a column containing a suitable adsorbing material. A selective developing agent is then passed through the column and the different substances in the solution are spread down the column into layers visibly separated from one another, provided the substances are colored. In the case of colorless substances, the layers of the different substances may be located by the use of ultra-violet light or by chemical tests.
This method was first described by the Russian botanist Tswett, in 1906. Tswett was engaged in the extraction and purifictaion of plant pigments.
Methods of chromatography have been applied to the separation of the rare earths and a number of procedures, based on chromatography techniques, have been developed for the separation of the inorganic cations and anions.
NOTES AND COMMENTARY
| are spread down … into layers -оседают пластами | provided -при условии, что was engaged in -занимался |
