# 8th Class Science Materials : Metals and Non-metals NCERT Summary - Man-Made Materials

NCERT Summary - Man-Made Materials

Category : 8th Class

Man-Made Materials

Soaps

• Soaps are sodium or potassium salts of higher fatty acids (organic acids that have more than 16 carbon atoms in their molecules) like stearic, palmitic and oleic acids.
• The sodium soaps are called hard soaps and the potassium soaps are known as soft soaps.

Differences between Soaps and Detergents

 Soaps Detergents They are metallic salts of long chain higher fatty acids, These are sodium salts of long chain hydrocarbons like alky1 sulphates or alkyl benzene sulphonates. These are prepared from vegetable oils and animals fats. They are prepared from hydrocarbons of petroleum or coal. They cannot be used effectively in hard water as they produce scum, i.e., insoluble precipitates of $C{{a}^{2+}},$ $M{{g}^{2+}},$ $F{{e}^{2+}},$ etc. These do not produce insoluble precipitates in hard water. They are effective in soft, hard or salt water. These cannot be used in acidic solutions. They can be used even in acidic solutions. Their cleansing action is not as strong as that of detergents, Their cleansing action is by surfactants, which is a strong cleansing action. These are biodegradable. Some of these are not biodegradable.

Detergents

• A detergent can be denned as 'the sodium or potassium salt of a long chain alkyl benzene sulphonic acid or the sodium or potassium salt of a long chain alky1 hydrogen sulphate that have cleansing properties in water'.
• A detergent is a non-soapy cleaning agent that uses a surface-active agent for cleaning a substance in solution.
• Synthetic detergents are described as soap-less soaps. Unlike soaps they are effective even in hard or salt water, as they form no scum.
• Modem synthetic detergents are alkyl or aryl sulphonates produced from petroleum (or coal) and sulphuric acid.
• Like soaps, detergents contain one large non-polar hydrocarbon group and one short ionic or highly polar group at each end, which allow for the cleansing action of dirt in water.
• From the environment point of view, the eco-friendly detergent is the need of the hour in order to have clean environment, green environment.

Fertilisers

• Fertilisers make crops grow faster and bigger so that crop yields are increased. They're minerals, which must first dissolve in water so that plants can absorb them through their roots.
• Fertilisers provide plants with the essential chemical elements needs for growth particularly nitrogen, phosphorus and potassium. The proportions of these elements in a fertiliser are often shown as N : P : K : : 15 : 30 : 15.
• The name of formula of a compound often suggests which elements are provided by a particular fertiliser.
• By looking at the harmful consequences of indiscriminate use of fertilisers, it has become our primary duty to go for green agriculture or organic agriculture by using biopesticide, herbal weedicide, green manure to preserve ecological imbalance by keeping in fact the food chain so that food production be assured.

Examples of Fertilisers, their Formula and the Essential Elements

 Fertiliser Essential Acid Alkali Ammonium nitrogen nitric ammonia Ammonium phosphate Nitrogen and phosphorus Phosphoric acid ammonia Ammonium sulphate Nitrogen Sulphuric acid ammonia Potassium nitrate potassium and nitrogen nitric acid potassium hydroxide

Glass

• Glass is an amorphous solid (non-crystalline) material that exhibits a glass transition, which is the reversible transition in amorphous material (or in amorphous regions within semi-crystalline materials) from a hard and relatively brittle state into a molten or rubber-like state.
• Glass is typically brittle and can be optically transparent. Soda-lime glass is composed of about 75% silicon dioxide $(Si{{O}_{2}}),\,$sodium oxide $(N{{a}_{2}}O)$from sodium carbonate$(N{{a}_{2}}C{{O}_{3}})$, lime$(CaO)$, and several minor additives. It is used for making windowpanes, tableware, bottles and bulbs.
• Silicate glass generally has the property of being transparent.
• Laminated glass: It can also be called bulletproof glass. Several layers of safety glass are bound together with a transparent adhesive.

 Type of Glass Special use Soft glass Ordinary glass for window panes, test tubes, bottles, etc. Hard glass For combustion tubes and chemical glassware High refractive index glass (Flint glass) For making lenses, cut glasses Pyrex glass For high quality glass apparatus, cooking utensils Crook's glass Absorbs ultraviolet rays, for making lenses Jena glass It is resistant to heat, shock and common reagent. It is used for making good quality glass wares.

Glass Pigment

 Compounds Colour Iron Oxides green, brown Manganese oxide deep amber, amethyst, decolouriser deep blue Gold chloride ruby red Selenium compounds red Carbon oxides amber/brown Mix of managanese, corblay, iron black Antimony oxides white Uranium oxides yellow green (glows) Sulphur compounds light blue, red Tin compounds white Lead with antimony yellow

Portland Cement

• Portland cement is composed of four major oxides: Lime$(CaO)$, silica$(Si{{O}_{2}})$, alumina$(A{{1}_{2}}{{O}_{3}})$ and iron.
• Also Portland cement contains small amount of magnesia$(MgO)$, alkalies$(N{{a}_{2}}O,\,and\,{{K}_{2}}O)$, and sulphuric anhydrite$(S{{O}_{3}})$.

Approximate Composition Limits of Oxides in Portland Cement

 Oxide Common Name Content, % $CaO$ Lime 66-67 $Si{{O}_{2}}$ Silica 17-25 $A{{l}_{2}}{{O}_{3}}$ Alumina 3-8 $F{{e}_{2}}{{O}_{3}}$ Iron 0, 5-6 $MgO$ Magnesia 0, 1-4 $N{{a}_{2}}O\,and\,{{K}_{2}}O$ Alkalies 0, 2-1, 3 $S{{O}_{3}}$ Sulphuric anhydride 1-3

DIFFERENT FORMS OF CARBON ALLOTROPY

Allotropy

• A phenomenon in which an element is found in different forms having different physical properties but similar chemical properties is known as allotropy.
• The different forms are called the allotropic or simply allotropes.
• Phosphorus, sulphur, carbon, etc. are elements which occur in different allotropic forms.

Carbon

• It has various allotropic forms, but these can be classified into crystalline form (diamond, graphite) and amorphous form (coke, coal, lamp-black, carbon black, animal charcoal, gas carbon, wood charcoal, etc.)

Crystalline Forms of Carbon

1. Diamond: Diamond is the purest form of carbon. It is found very deep inside the Earth, including South Africa, Congo, and Angola. Of late, synthetic diamonds have also been prepared.

Properties

(i) It is the hardest natural substance.

(ii) It is insoluble in any solvent.

(iii) It is of specific gravity 3.5.

(iv) It is non-conductor of heat and electricity.

(v) It bums in air at $900{}^\circ C$ and gives out $C{{O}_{2}}$.

(vi) It occurs as octahedral crystals.

(vii) It is transparent and has refractive index of 2.45.

(viii) It occurs in the free state.

Uses

(i) It is used in making jewellery.

(ii) It is used for cutting hand tools.

(iii)  For drawing thin wires, diamond dies are used.

1. Graphite: Also called as black lead. As compared to diamond, it is widely available in nature in countries like India, Sri Lanka, Canada, Russia, etc. It can also be produced artificially by heating anthracite coal with little iron oxide of silica in electric furnace.

Properties

(i) It is soft.

(ii) Its specific gravity is 2.3.

(iii) It is good conductor of heat and electricity.

(iv) It is black in colour.

(v) It is insoluble in ordinary solvents.

(vi) It bums in air at $700-800{}^\circ C$ and gives out $C{{O}_{2}}.$

(vii) It is of hexagonal crystals.

Uses

(i) It is used in writing pencils and lead.

(ii) It is used as a lubricant for high temperature.

(iii) It is used as refractory materials for designing crucibles and electrodes for high temperature.

(iv) It is used in electro-typing and manufacturing of gramophone records for making the non-conducting surface as conducting.

Amorphous Forms of Carbon

1. Coal: Its common variety is bituminous which is like hard stone and bums with smoky flame. The superior quality coal bums without smoke and is called anthracite. It is formed out of carbonisation of organic and fossil matter buried deep into the Earth, under high pressure and high temperature with very-very limited supply of air, for centuries. Anthracite, Bituminous, Lignite and Peat are the types of coal with decreasing carbon percentage.

Uses

(i) It is used as a fuel.

(ii) It is used in the manufacturing of coal gas. The by-products of this process are coke, coal tar, ammonical liquor. Coal-tar is a source for making dyes, explosives, chemicals, etc.

(iii) It is also used in manufacturing fuel gases like producer gas. Water gas and semi-water gas.

(iv) It is used for manufacturing of synthetic petrol by catalytic hydrogenation of coal.

1. Coke: It is a coal deprived of volatile constituents such as coal gas, ammonia, benzene, phenol, tar, etc. It is manufactured from coal by destructive distillation by heating in the absence of air due to which volatile constituents are left back in the coal.

Uses

(i) It is used as fuel.

(ii) It is used for making graphite and water gas.

(iii) It is used as reducing agent in iron and steel industry.

1. Wood Charcoal: When wood is suitably stocked, encased in an earthy clay cover and ignited with a very limited supply of air, the volatile products are allowed to escape, and wood charcoal is obtained.

Uses

(i) It is used as a fuel.

(ii) It is used a constituent of gun-powder.

(iii) It is used for purification of water.

(iv) It is used as deodorant and decolourising agent in sugar solution and gas masks.

1. Bone Black or Animal Charcoal: When bones are subjected to destructive distillation in a retort, the residue obtained is boneblack or animal charcoal.

1. Lampblack: When tar or vegetable oil rich in carbon, is burnt in an insufficient supply of air, black soot is deposited on the wet blankets hung in the room.

Uses

(i) It is used in making India ink.

(ii) It is used in making printers ink.

(iii) It is also used by ladies for eyelids decoration.

1. Carbon Black: It is obtained by burning natural gas in the presence of limited supply of air and collecting the soot on the underside of a revolving disc which is scrapped off and packed.

Uses

(i) It is used in the rubber for making automobile tyres.

(ii) It is used as a replacement of lamp black used for many a purpose.

1. Gas Carbon and Petroleum Coke: Gas carbon is produced by scrapping the carbon from the walls of the retort formed as a result of destructive distillation of coal.
• When distillation of crude petroleum is done in a retort, the petroleum coke is deposited on the walls of the retort.

Use

• It is used for making electrodes when pressed into sticks, as both are conductors of electricity.

1. Sugar Charcoal: It is the poorest form of carbon.

(i) It is obtained when sugar is heated strongly out of contact with air.

(ii) It can be liquefied even to room temperature but under high pressure.

• Further, it can be converted into a solid state, known as dry ice which is used as a mobile refrigerant.

1. Carbon-14: Carbon-14 is a useful radioactive isotope for tracer studies in organic and bio-chemical system, including the determination of the age of materials that were once alive. The identity and amount of many elements. Present in trace amounts n mixtures may be detennined by neutron activation analysis. This procedure inversion of non-radioactive isotopes of chemical element and the determination of the type and intensity of the radioactivity that results.

##### Notes - Man-Made Materials

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