CBSE Class 10 Chemistry Chemical Industry Notes Set 13

Glass

Glass is a transparent, amorphous mixture of silicates, usually of sodium and calcium, made by fusing sand (silica) with soda ash and limestone at about 1500°C and cooling it slowly (annealing) to remove strain. It is often called a supercooled liquid as it has no definite melting point.
1. Soda glass: soft, melts easily; windows and bottles.
2. Potash (hard) glass: contains potassium carbonate; resists heat, used for chemical apparatus.
3. Borosilicate (Pyrex): tolerates sudden heat changes.
4. Lead (flint) glass: bright and heavy, used for lenses and cut glass.
5. Special kinds: laminated (safety) glass with a plastic layer, fibre glass, Crookes glass (absorbs ultraviolet) and coloured glass.
Colours: cobalt oxide gives blue, manganese dioxide violet, cuprous oxide red, ferric oxide brown or yellow and chromic oxide green.

Cement

Cement is made by heating limestone and clay in a rotary kiln at about 1500°C to form clinker, which is cooled and ground with 2 to 3 percent gypsum. Gypsum slows the setting. Average composition: lime 60 to 67%, silica 17 to 25%, alumina 3 to 8%, with small amounts of iron oxide, magnesia and sulphur trioxide. The setting of cement is a chemical process, hydration. Concrete is cement with sand and gravel; reinforced concrete contains steel rods or mesh.

Plastics

Plastics are synthetic polymers that can be moulded. Thermoplastics soften on heating and can be reshaped (polythene, PVC, polystyrene). Thermosetting plastics harden permanently when moulded because of cross-linking (bakelite, melamine). Addition polymers form from alkenes; condensation polymers form with loss of small molecules such as water.

Fibres and Rubber

Natural fibres: cotton, wool, silk. Semi-synthetic: rayon (regenerated cellulose). Synthetic: nylon (hexamethylenediamine and adipic acid), terylene (terephthalic acid and ethylene glycol).
Natural rubber is a polymer of isoprene. Vulcanisation is heating rubber with sulphur to make it harder, stronger and more elastic. Synthetic rubbers include neoprene, Buna and thiokol.

Soaps, Detergents and Matches

Soap is the sodium or potassium salt of a fatty acid, made by boiling fat or oil with alkali (saponification). It forms scum with calcium and magnesium of hard water, so detergents (salts of sulphonic acids) are better in hard water. In safety matches antimony trisulphide and potassium chlorate are in the head and red phosphorus is on the box; strike-anywhere matches contain phosphorus sesquisulphide, P₄S₃.