2. Answer the questions

1. Which is the most abundant element found in the Earth’s crust?

2. What are the properties of silicon?

3. At what temperature does silicon melt?

4. What compounds does silicon form?

5. Where is high-purity silicon used?

6. With what elements does silicon form useful and important compounds?

Cellulose

Cellulose (C6H10O5) is a naturally occurring carbohydrate. The molecular chains are essentially linear. Cellulose is a colourless solid, of specific gravity about 1.5 (one point five), insoluble in water and in all organic solvents.

Wood contains 40-50 per cent cellulose. Wood cellulose which has been separated from impurities by chemicals is called wood pulp.

Highly purified cellulose derived from cotton is termed cotton pulp. Cellulose fibres used in their natural form are termed natural celluloses. In this group are cotton, linen, jute, hemp etc.

Cellulose derivative solutions are characterized by high viscosity. This viscosity is largely determined by the degree of polymerization of the cellulose used in a given manufacturing process.

Natural cellulosic fibres, for example cotton and linen, are widely used in textile.

Cellulose from wood, straw, grasses, cotton rags and linters is used for making paper. Regenerated and chemically modified cellulose is used for making fibres, films, plastics, adhesives, explosives, protecting coatings and thickening agents.

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

Exercises

1. Answer the questions.

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?

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 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.