Methods of separation

METHODS OF ANALYSIS

ANALYTICAL CHEMISTRY

Answer the questions.

EXERCISES

VOCABULARY

naturally occurring – той,що зустрічається в природі essentially – по суті specific gravity=specific weight – питома вага to separate from impurities – відокремлювати від домішок wood pulp – деревна целюлоза purified - очищений cotton pulp – бавовняна маса fibre - волокно linen - льон jute - джут

hemp -коноплi degree - ступінь straw - солома cotton rags – дрантя cotton linter – лінтер (бавовняний пух) regenerated - відновлений film - плівка protecting coating – захисне покриття thickening agent – згущувач

1. What is cellulose?

2. What are the properties of cellulose?

3. How much cellulose does wood contain?

4. What is wood pulp?

5. What is highly purified cellulose called?

6. Where are natural cellulose fibres used?

7. What cellulose is used for making paper?

8. What is regenerated and chemically modified cellulose used for?

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 has been developed for almost everything from Aluminium to Zirconium.

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 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 liquefied 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.

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