by • 14/07/2011 • 9th class ChemistryComments (0)881

Q1) what is allotropy? describe chief allotropic form of carbon.
ans) allotropy:- various form of the same element which have same chemical properties but different physical properties are called allotropic forma or allotropes and the phenomenon is called allotropy.
allotropic forms of carbon:-
1) diamond
2) graphite
1)diamond:-diamond is a transparent and bright. it is the hardest of all naturally occurring substances. it is used commercially for cutting glass, drilling rocks and ornamental purposes. it is a non conductor of heat and electricity.
2)graphite:- it is grayish black and very soft. it is used in making lead pencles.graphite is a good conductor of electricity. it is not affected by acids or is used as electrodes in many electrolytic processes.


Q2) describe the laboratory and industrial preparation of carbon dioxide. what is the action of carbon dioxide on:
1)magnesium (2) carbon (3) lime water.
ans) laboratory preparation of carbon dioxide:- it is prepared in the laboratory by the action of dilute acid on metal carbonates or bicarbonates.
industrial preparation of carbon dioxide:- carbon dioxide is obtained on commercial scale by heating lime stone in a furnace.
carbon dioxide is also obtained as a by product during the production of alcohol from molasses by fermentation in the presence of yeast.
1) action on megnesium:- highly reactive metals like magnesium continue to burn in presence of carbon dioxide forming MgO.
2) action on carbon:-carbon dioxide is reduced to carbon monoxide when heated in presence of carbon which have sufficient chemical affinity for oxygen.

3) action on lime water:- when carbon dioxide is passed through lime water it is turned milky due to the formation of calcium carbonate.





Q3) what is glass? how is it manufactured? discuss types of glass with their usefulness?
ans) glass:-glass is an inorganic super cooled liquid having no definite melting point and has high viscosity to present.its crystallization. glasses are formed by allowing molten silicate to cool.
types of glass:
1) ordinary window glass or soda glass:- it prepared by heating a mixture of silica sodium carbonates and calcium carbonate in a furnace.
uses:- it is used in making bottles, windows and all kinds flat glass.
2)borosilicate glass:- borosilicate glass is prepared from silica boronoxide,aluminuimoxide,and sodiumoxide.this glass is commonly known as Pyrex.
uses:it is used for some kitchen and laboratory wares such as ovenware,beakers,flask and test tube.
3) crystal glass:-crystal glass is made from silica lead oxide, potassium carbonate and calcium carbonate.
uses:- it is heavy glass which can be cut to give decorative glass ware.
4) colored glass:- glass can be prepared in different colors by the addition of small quantities of contain metallic oxide or salt to molten glass.
5) water glass and silica gel:- sodium silicate is known as water glass. it is prepared by heating a mixture of silica and sodium carbonate.
uses:- water glass is used for various fire proofing materials.
soda glass:-when an acid is added to a solution of water glass it turns into a jelly like state known by chemist as a gel. on dehydrating this gel by heating a hard porous material is formed. this is called silica gel and it is used to absorb gases and vapor.
6) fiber glass:-glass fiber is produced by dropping molten glass into a rotating refectory disc. the glass files off the disc forming fiberglass.fiber are mixed with plastic are used to mould car and boat bodies water tanks and sports good.


Q4) how can nitrogen be prepared in the laboratory? what is the action of N2 on:-
1)CaC2 (2) H2 (3) Ca
ans) laboratory preparation:- pure nitrogen is obtained in the laboratory by the following method.
1) by heating a mixture of sodium nitrite and aqueous solution of ammonium chloride.
2) by heating ammonium dichromate.
3) by the fractional distillation of air.
nitrogen can be obtained by the fractional distillation of liquid air. air from which carbon dioxide has been removed is liquified by successive compression and expansion at low temperature.
upon distillation nitrogen gas is evolved first at-196c and thus separated from oxygen.

1)action on CaC2:- calcium cyan amide is obtained by passing nitrogen over red hot calcium carbide.
2) action on H2:-if a mixture of hydrogen and nitrogen is heated at 400-450c in the presence of iron oxide and aluminum sulphate under 200 atmospheric pressure it is converted to ammonia.
3) action on calcium:-calcium is converted to calcium nitrides when heated in a current of nitrogen.
Q5) describe haber process for the manufacture of ammonia.
ans) this is the most important synthetic method for a large scale preparation of ammonia. a mixture of pure nitrogen and hydrogen in the proportion of 1:3 by volume is compressed to 200 atmospheric pressure and then passed over iron oxide and alumminuim sulphate as catalyst(iron containing a little molybdenum) at 400-450c million of tons of ammonia are prepared annually by this method.

Q6) how is nitric acid manufactured from ammonia by ostward method?what is the action of HNO3 on:
1) CuO (2) Cu (3) Mg
ans) nitric acid is obtained on a large scale by the oxidation of ammonia. if a mixture of ammonia and air is heated up to 600c in the presence of platinum nitric oxide if produced.
this an exothermic process and large amount of heat is evolved for this reason the chemical process continue and nitric oxide is converted to nitrogen peroxide in the presence of excess air.
nitrogen peroxide formed above react with water to from nitric acid.
1) action on CuO:- when copper oxide is reacted with nitric acid it produced copper nitrate and water.
2)action on copper: when copper is reacted with dilute nitric acid it produced copper nitrate ,nitric acid and water.
3) action on Mg: when Mg react with nitric acid it produced magnesium nitrate and hydrogen gas is evolved.
Mg+2HNO3 Mg(NO)3+H2

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