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901.

Explain the cleansing action of soap

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Solution :(i) The negative and POSITIVE ends of SOAP
(ii) INTERACTION of POLAR end of soap with WATER .
(iii) Decrease in surface tension ofwater.
Discussion
902.

Explain the chemical reaction of chlorine with hydrogen sulphide.

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SOLUTION :`H_2S+CL_2rarr2HCLuarr+S`
Discussion
903.

Explain the changes observed when a glass of water is placed on the surface of moon.

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SOLUTION :(i) RELATIVE pressure on the SURFACE of the moon.
(II) Effect of pressure on evaporation of water.
Discussion
904.

Explain the basic working of the Castner-Kellner cell, used for producing Naoh (sodium hydroxide).

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Solution :(i) Mercury.
(ii) Intermediate electrode.
(iii) Anode, cathode.
(IV) Brine solution.
(V) ELECTROLYTIC dissociation of NaCl.
(VI) Liberation of chlorine gas.
(vii) Formation of sodium amalgam.
(viii) Formation of sodium hydroxide.
Discussion
905.

Explain the acidic nature of sulphur dioxide based on its reactivity with water

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SOLUTION :`H_2O+SO_2rarrH_2SO_3`
Discussion
906.

Explain in detail how sulphuric acid is prepared by the Contact process

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SOLUTION :Preparation of sulphur dioxide.
(ii) Vanadium PENTOXIDE.
(iii) Preparation of sulphur trioxide.
(iv) Pyro SULPHURIC ACID.
(v) Water treatment of pyro sulphuric acid.
Discussion
907.

Explain how the result of alpha-ray scattering experiment led to Rutherford's model of atom. Give the postulates and drawbacks of Rutherford's atomic model.

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SOLUTION :MODEL:
(i) Nucleus and EMPTY SPACE.
(ii) Revolution of electrons.
Drawbacks :
(i) Instability of atom.
Discussion
908.

Explain how sugar charcoal is prepared.

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SOLUTION :DESTRUCTIVE DISTILLATION of SUGAR
Discussion
909.

Explain how are the following mixtures separated? (a) NH_(4)Cl-NaCl mixture (b) Sand - sawdust mixture (c ) Chalk - water mixture

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SOLUTION :(i) Type of COMPOUNDS
(ii) Suitable SEPARATION technique used to SEPARATE
Discussion
910.

......................exists in the form of buckyball and nanotubes.

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ANSWER :FULLERENE
Discussion
911.

Evaporation can take place at any temperature, but boiling takes place at a fixed temperature. Give approprate reasons.

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Solution :(i) Differences between evaporation and BOILING.
(ii) COMPARISION of the part of the liquid from where evaporation and boiling take place.
(iii) CONDITION at which boiling starts in a liquid.
Discussion
912.

Establish water as a compound.

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SOLUTION :(i) CONSTITUENTS of WATER
(II) SYNTHESIS of water
Discussion
913.

Establish antimony as a metalloid on the basis of its metallic property.

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SOLUTION :CONDUCTION of ELECTRICITY by ANTIMONY
Discussion
914.

Equal volumes of nitrogen and oxygen react to give "___________"

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SOLUTION :NITRIC OXIDE(NO).
Discussion
915.

The energy possessed by a body due to its motion is called ................ energy

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SOLUTION :KINECTIC ENERGY
Discussion
916.

Electrons revolve around the nucleus in definite orbits called .........

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SOLUTION :ENERGY SHELLS
Discussion
917.

Electrons are distributed in different energy shells, according to the rules of ..........scheme.

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SOLUTION :Bohr-Bury SCHEME
Discussion
918.

Electron present in ______ orbit cannot lose its energy.

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ANSWER :FIRST
Discussion
919.

Electrolysis of molten sodium chloride produces sodium and chlorine. Is this reaction a red.ox reaction? Give reasons in support of your ans\:ver.

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Solution :During electrolysis of molten sodium chloride, sodium is deposited at cathode and chlorine is liberatedat anode. Since removal of more electronegative ELEMENT from NaCl gives sodium, the PROCESS is CALLED reduction. Since removal of more ELECTROPOSITIVE element from NaCl gives chlorine, the process is called oxidation. Therefore, the electrolysis of molten sodium chloride is called redox REACTION.
Discussion
920.

Electric bulbs are filled with argon gas but not air. Explain.

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Solution :Argon is uesd in FILLING the ORDINARY electric bulbs because it is inert. Air containing oxygen cannot be USED because it causses OXIDATION of tungsten. Moreover nitrogen and oxygen present in air can REACT at the high voltage to give nitric oxide.
Discussion
921.

Efflorescent substances .....................water when exposed to air.

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ANSWER :LOSE
Discussion
922.

Each small unit of a synthetic fibre is a/an_______ substance.

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ANSWER :B
Discussion
923.

Each radical takes part as a whole in chemical reactions and has its own valency.

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ANSWER :T
Discussion
924.

Dust particles from air are removed by passing air through _______ or ______.

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SOLUTION :PRECIPITATORS, FILTERS
Discussion
925.

Durning of candle is an example of both physical and chemical changes. Justify your answer.

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Solution :(i) Melting of WAX.
(II)DECOMPOSITION of HYDROCARBONS.
Discussion
926.

During the sunnner vacation, a chemistry laboratory assistant stored the chemicals in their respective bottles.After a few months it was observed that the lids of the bottles in which sodium hydroxide was stored was struck tight, He went to a lecturer for finding the solution for this problem.What solution could be suggested by the lecturer

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SOLUTION :Sodium hydroxide on being EXPOSED to air reacts with the `CO_2` present in the air to FORM sodium carbonate.This solidifies and the lid gets stuck DUE to this.The lids can be REMOVED by using dilute acid with the help of cotton.
Discussion
927.

During the separation of acetone from water by fractional distillation, following steps are carried out. Arrange the following in a proper sequence. (a) Water remains in the distillation flask. (b)The acetone - water mixture is taken in a distillation flask and the flask is heated at a temperature equal to or more than the boiling point of acetone but less than that of water. (c ) As the vapour pass through the fractionating column, they get condensed and the liquid formed is collected in the receiver. (d) When the mixture in the flask is subjected to slow heating, acetone, being more volatile than water, gets vapourised first.

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B d C a
b d a c
c a b d
c a d b

Solution :(i) The acetone water mixture is passed into the distillation flask and the flask is heated at a temperature equal to or more than theboiling point of acetone but less than that of water.
(ii) When the mixture in the flask is subjected to slow heating, acetone, being more volatile than water, gets vapourised first.
(iii) As the vapours pass through the FRACTIONATING column, they get condensed and the LIQUID formed is collected in the receiver.
(iv) Water remains in thedistillation flask.
Discussion
928.

During the separation of immiscible liquid-liquid mixture by separating funnel, following steps are followed. Arrange them in a proper sequence (a) The nozzle tap is opened slowly and the heavier component is allowed to trickle down. (b) The liquid - liquid mixture is poured into the separating funnel clamped vertically. (c) The lighter component remains in the flask. (d) Mixture is allowed to stand where clear layers of liquids are formed. (e) The liquid with higher density settles down at the bottom of the flask.

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b d a e c
a b c d e
b d e a c
d a b c e

Solution :(i) The LIQUID - liquid mixture is poured in to the SEPARATING funnel clamped VERTICALLY.
(ii) Mixture is allowed to stand where clear layers of liquids are formed.
(iii) The liquid with higher density settles down at the bottom of the flask.
(iv) The nozzle tap is opened slowly & the heavier component is allowed to trickle down.
(v) The lighter component remain in the flask
Discussion
929.

During the process of soldering, the metal surfaces are cleaned using acids. What purpose does this serve and which separation technique is involved in this?

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Solution :(i) The PHENOMENON FO SOLDERING.
(ii) Composition of metal surface.
(iii) Effect of addition of acid to metals.
(iv) PROCESS of SEPARATION.
Discussion
930.

During photosynthesis, energy is ………………. And during burning, energy is ………………. .

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SOLUTION :ABSORBED, RELEASED
Discussion
931.

Due to its high _____, water is called as universal solvent.

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ANSWER :DIELECTRIC CONSTANT
Discussion
932.

Dry powders like _______ and __________ release carbon dioxide when spread near fire.

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ANSWER :A::B::C::D
Discussion
933.

Dry ice should not be stored in sealed bottle. Explain with appropriate reason.

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Solution :(i) PROPERTIES of dry ICE .
(ii) CHANGE in dry ice at normal TEMPERATURE and pressure conditions.
(iii) COMPARISON of volume before and after the change.
Discussion
934.

Draw a comparison among petrol, LPG and CNG as automobile fuels.

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Solution :Petrol is a fraction containing hydrocarbons with more than five carbon atoms `(C_(5)-C_(10))`. LPG contians butane as a major component with four carbon atoms. CNG CONTAINS methane with one carbon atom as a major component. With decrease in number of carbon atoms in the hydrocarbon, the CALORIFIC value increases and alos the extent of incomplete COMBUSTION decreases . Therefore, the fuel efficiency increases. Apart from this, petrol contains sulphur and nitrogen which release harmful pollutants into the atmosphere whereas LPG and CNG do not CONTAIN sulphur and nitrogen. Petrol being a liquid leaves residue in the engine. Among LPG and CNG, burning of CNG PRODUCE less amount of `CO_(2)` than LPG. Hence CNG is considered as the best fuel.
Discussion
935.

Does your city/town have a fire brigade station?

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ANSWER :YES, my city/townhas a FIRE BRIGADE STATION.
Discussion
936.

Does a matchstick burn by itself? How does it burn?

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Answer :No, a matchstick does not BURN by itself. It BUMS when it is RUBBED against the corner of the matchbox.
Discussion
937.

Do you know where the smoke could have come from?

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Answer :The smoke in the ATMOSPHERE mainly comes from the man-made SOURCES like industries, POWER plants, automobile exhausts, etc. Besides, natural sources of smoke are also from forest FIRES or volcanic ERUPTIONS.
Discussion
938.

Do these experiences tell you that different substances catch fire at different temperatures?

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Answer :YES, different SUBSTANCES catch FIRE at different TEMPERATURES as every substance has different ignition temperature.
Discussion
939.

Do non-metals react with water?

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ANSWER :No, non-metals do not REACT with WATER.
Discussion
940.

Disposal of plastic is a major problem. Why?

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Answer :Disposal is major problem because:(i) It is a non-biodegradable SUBSTANCE.(II) It is not ENVIRONMENT FRIENDLY as it causes environment pollution.
Discussion
941.

Discuss three importance uses of (i) Graphite (ii) Wood Charcoal (iii) Carbon monoxide (iv) Sugar charcoal (v) Bone charcoal (vi) Carbon dioxide (vii) Methane.

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Solution :(i) Lead of PENCILS, moderator in nuclear reactors, marking refractory CRUCIBLES.
(ii) Deodrant and disinfectant , gas masks, fuel for keeping rooms warm in WINTER .
(iii) Reducing agent in the extraction of metals, manufacture of chemicals , fuel.
(iv) Extracting metals from their oxides, adsorbent material, making artificial diamonds.
(v) Removes colour from sugarcane JUICE, extraction , of yellow phosphorous, fertilizer industries.
(vi) Soft DRINKS or aerated drinks, fire extiguishers, production of industrial compounds.
(vii) Fuel, parent hydrocarbon for halogenations reactions, water gas preparation.
Discussion
942.

Discuss the physical properties of (i) Cac_(2) ""(ii) SiC "" (iii) CaCO_(3) "" (iv) Na_(2)CO_(3) "" (v) NaHCO_(3)

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Solution :(i) GREYISH black crystalline SOLID , M.P. `2300^(@)C`, non- conductor of electricity .
(II) Insoluble in `H_(2)O`, density 3.22 g/`cm^(3)`, hard substanceM.P. `2700^(@)C`.
(iii) White crystalline solid with M.P. `825^(@)C`, insoluble in `H_(2)O`.
(iv) White crystalline solid with M.P. `851^(@)C`, insoluble in `H_(2)O`.
(v) White crystalline, SPARINGLY soluble in water.
Discussion
943.

Discuss the physical properties of chlorine

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SOLUTION :Greenish yellow, pungent smell, sparingly. SOLUBLE in water heavier than air, vapour DENSITY. 35.5 and ATOMICITY 2.
Discussion
944.

Discuss the method of preparation of bleaching powder.

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Solution : gas,slaked LIME.
(II) Chlorinating tower.
(III) Counter current mechanism
Discussion
945.

Discuss the laboratory preparation of carbon monoxide .

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SOLUTION :(i) Reactant
(II) Conditions
(iii)PRECAUTIONS.
Discussion
946.

Discuss the different physical properties of water with respect to the various uses.

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Solution :(i) Nature
(ii) Freezing POINT
(iii) Boiling point
(iv) Density
(V)Conductivity
(vi) Specific HEAT
(vii) LATENT heat of fusion and evaporation
(viii) Solvent PROPERTY
Discussion
947.

Discuss the characteristics/properties of plastics.

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Answer :The characteristics/properties of PLASTICS are(i) Non-reactive(II) LIGHT, strong and DURABLE.
Discussion
948.

Discuss the change in energy and arrangement of molecules on increasing the temperature of ice from =5^(@)C" to " 10^(@)C at 1 atm pressure.

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Solution :On heating ice at `-5^(@)C,` its temperature increases up to `0^(@)C,` i.e, the KINETIC energy of the molecules increases. At `0^(@)C`,the ice starts to melt . During this period the energy suppliedis taken up to increase the potential energy of the molecules and the ARRANGEMENT of molecules changes. Once the ice cube melts, the heat energy suppliedis againused to increase the temperature of water due to increase in kinetic energy of the molecules. However from `0^(@)C " to " 4^(@)C`, the molecules of water come closer and above `4^(@)C` the molecules MOVE farther AWAY.
Discussion
949.

Discuss in detail Bosch process of preparation of hydrogen gas.

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Solution :(i) Principle
(ii) Balanced chemical EQUATIONS
(III) Process
(IV) Corresponding equations
Discussion
950.

Discuss carbon cycle in nature.

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SOLUTION :(i) Source of CARBON
(ii) TRANSFER of carbon to VARIOUS LEVEL.
Discussion