CBSEClass9Science

ImportantQuestions

Chapter1

MatterinOurSurrounding

1MarksQuestions

1. Whichofthefollowingarematter?

Chair,air,love,smell,hate,almonds,thought,cold,colddrink,smellofperfume.

Ans.Chair,air,smell,almonds,colddrinkandsmellofperfumearematter.

2. ConvertthefollowingtemperaturetoCelsiusscale:

i) 300K

ii) 573K

Ans.i)

ii)

3. Whatisthephysicalstateofwaterat:

a.

b.

Ans. b. is the boiling point of water hence at both the temperatures water is in

gaseousstatei.e.watervapour.

4. Foranysubstance,whydoesthetemperatureremainconstantduringthechangeof

state?

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CBSEClass9Science

ImportantQuestions

Chapter1

MatterinOurSurrounding

2MarksQuestions

1. Givereasonsforthefollowingobservation:

Thesmellofhotsizzlingfoodreachesyouseveralmetersway,buttogetthesmellfrom

coldfoodyouhavetogoclose.

Ans.Sincehotsizzlingfoodhastemperaturehigherthancoldfoodandathigher

temperaturediffusionrate(movement)ofparticlesisveryfastduetothisthesmellofhot

sizzlingreachesusfromseveralmetersaway.

2. Themassperunitvolumeofsubstanceiscalleddensity.

(density=mass/volume).

Arrangethefollowinginorderofincreasingdensity–air,exhaustfromchimneys,

honey,water,chalk,cottonandiron.

Ans.Arrangingsubstancesintheirincreasingorderofdensities:

Air<exhaustfromchimneys<cotton<water<honey<chalk<iron.

3. Liquidsgenerallyhavelowerdensityascomparedtosolids.Butyoumusthave

observedthaticefloatsonwater.Findoutwhy.

Ans.Icerepresentssolidstateofwater.Ifweobserveits3Dstructure,alargeemptyspaceis

foundinsideiceasaresultitbecomeslessinweightascomparedtowater.Duetoitsspecific

structurethoughsolid,icefloatsonwater.

4. Whydoesadesertcoolercoolbetteronahotdryday?

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Ans.Onahotdrydayrateofevaporationisfaster.Inadesertcoolerwhenexhaustfanison,

hotairentersthroughthestrawmatesandatthissiteevaporationofwatertakesplaceand

thatalsoatfasterrate.Ittakesawayheatfromairsotheairbecomescoolevencoolerona

hotdryday.

5. Howdoesthewaterkeptinanearthenpot(matka)becomecoolduringsummer?

Ans.Duringsummersthewaterpresentonthesurfaceoftheearthenpotevaporateswhich

causesthecoolingeffect.Besidesearthenpotbearsporesonithenceevaporationoccurs

continuouslysoiscooling.

6. Whydoesourpalmfeelcoldwhenweputsomeacetoneorpetrolorperfumeonit?

Ans.Someliquidsgetquicklyvapourisedandtheyarecalledvolatileliquids.Acetone,petrol

andperfumearealsovolatileliquidsthereforetheygetheatfromourpalmandcause

cooling.

7. Whyareweabletosiphotteaormilkfasterfromasaucerratherthanacup?

Ans.Saucerhasabiggersurfaceareaascomparedtocup.Sinceevaporationisasurface

phenomenon,byusingasaucerinsteadofcupweareincreasingthesurfacearefor

evaporationtooccur.Fasterevaporationofparticlesofteaormilkallowscoolingandtaking

asipbecomeseasier.

8. Whattypeofclothesshouldwewearinsummer?

Ans.Cottonisagoodabsorbantofwaterhenceitabsorbssweatquitewellandporesinthe

fabricexposethatsweattoeasyevaporationhenceweshouldpreferwearingcottonclothes

insummer.

9. Convertthefollowingtemperaturestothecelsiusscale.

(a) 293K(b)470K.

Ans.a)

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b)

10. ConvertthefollowingtemperaturestotheKelvinscale.

(a) 25°C

(b) 373°C.

Ans.a)

b)

11. Givereasonforthefollowingobservations.

(a) Naphthaleneballsdisappearwithtimewithoutleavinganysolid.

(b) Wecangetthesmellofperfumesittingseveralmetresaway.

Ans.a)Somesubstancespossessthepropertyofsublimationlikecamphorandnaphthalene

balls.Suchsubstancesdirectlychangefromsolidtogaseousstatewithoutchanginginto

liquidlikeice→water→watervapourdoes.Therefore,naphthaleneballsdisappearwithtime

withoutleavinganysolid.

b) Beingavolatilesubstance(getsevaporatedeasily)perfumeschangefromliquidto

gaseousstateveryfast.Thoseparticlesmixupwithairparticlesanddiffusetoreachour

nostrilssuchthatwegetthesmellofperfumesittingseveralmetresaway.

12. Givetworeasonstojustify—

(a) wateratroomtemperatureisaliquid.

(b) anironalmirahisasolidatroomtemperature.

Ans.a)Theroomtemperatureisgenerallyalwaysmorethan andlessthan and

withinthisrangewaterisaliquidsowateratroomtemperatureisaliquid.

b) Themeltingpointofironismuchhigherthantheroomtemperaturethereforeaniron

almirahisasolidatroomtemperature.

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13. Whyisiceat273Kmoreeffectiveincoolingthanwateratthesametemperature?

Ans.Whilemeltingiceabsorbslatentheatofmeltingfromthesurroundingsandgets

changedintowaterthatmakesthecoolingeffectmoreintenseascomparedtowateratsame

temperature.

14. Whatproducesmoresevereburns,boilingwaterorsteam?

Ans.Ascomparedtoboilingwateritisobservedthatsteamproducesmoresevereburns

sinceasthesteamchangesintoboilingwateritreleasesheatofcondensationwhichis

equivalenttolatentheatofwaterresultismoresevereburning.

15. Whatisevaporation?Whatarethefactorsaffectingit?

Ans.Evaporationistheprocessbywhichwater(liquid)changestovapoursatany

temperaturebelowitsboilingpoint.

Factoronwhichevaporationdepends:

(a) Surfacearea

(b) Humidity

(c)Windspeed

(d) Temperature

16. Whathappenwhenweapplypressuretotheparticlesofmatter?

Ans.Whenweapplypressuretotheparticlesofthematter,thentheparticlescomecloserto

eachotherbecausepressureistheforceappliedpercross-sectionalareasotheforceapplied

bringstheparticleclosertoeachother.

17. Definelatentheatofvaporizationandlatentheatoffusion.

Ans.Latentheatofvaporizationistheheatenergyrequiredtochange1kgofaliquidtogas

atatmosphericpressurewithoutchangingitsstate.

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Latentheatoffusionistheamountofheatenergyrequiredtochange1kgofsolidintoliquid

withoutchangingitsstate.

18. IfthemeltingpointofanobjectAishighthenwhatstateyouexpectittobeatroom

temperature?

Ans.Meltingpointisthetemperatureatwhichasolidmelts/changeintoaliquidstate.So,if

themeltingpointofanobjectAishighermeansthatitrequiresgreatertemperatureto

changeintoliquidtheobjectwillremainthesameatroomtemperaturebecauseroom

temperatureislessandtheobjectcannotchangeitsstate.

19. Whathappenswhenthetemperatureofthesolidsincrease?

Ans.Whentemperatureofthesolidisincreased,kineticenergyoftheparticlesincreasesas

resultsparticlesvibratesmorefreelywithgreaterspeed.Theyovercometheforceof

attractionbetweentheparticlesandstartmovingmorefreely.

20. Whenheatisbeingsuppliedtoasolid,thenwhatdoestheheatenergydotothe

particlesofsolid?

Ans.Theheatsuppliedtothesolid,helpstheparticlestoovercometheforcesofattraction

betweenthemandincreasestheirkineticenergy,asaresultofwhichparticlebreakfreethe

forcesofattractionandchangestoliquidstate.

21. Whyisitthatonincreasingthewindspeedtherateofevaporationincreases?

Ans.Whenthespeedofwindincreases,thentheyblowawaywiththemthewatervapourin

theairandasresultsevaporationwillincreasebecausethesurroundingairwillbeableto

receivemorevapoursandhenceevaporationincreases.

22. Whydowesaythatevaporationisasurfacephenomenon?

Ans.Evaporationiscalledasurfacephenomenonbecauseonlyparticlesofthesurfaceof

liquidgainsenergyandchangesintovapours.

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Ans.Duringthechangeofstatetheheatorenergyprovidedtoparticlesofmatterisutilized

totaketheparticlesofmatterapartfromeachotherasaresultthetemperatureofsubstance

ormatterremainsconstantduringchangeofstate.

5. Suggestamethodtoliquefyatmosphericgases.

Ans.Ifwe decrease temperature and increasing pressurewe can liquefy the atmospheric

gases.

6. Arrangethefollowingsubstancesinincreasingorderofforcesofattractionbetween

theparticles—water,sugar,oxygen.

Ans.Oxygen<water<sugar.

7. Whatisthephysicalstateofwaterat—

(a) (b) (c) ?

Ans.At25°Cwaterisliquid,at waterissolid(ice),at waterisgas(watervapour).

8. Ifthehumidityintheairincreasethentherateofevaporation:

(a) decrease

(b) increase

(c) remainsame

(d) both(b)and(a)dependinguponthetemperature

Ans.(a)decrease

9. Whichofthefollowingstatementiscorrect?

(a) boilingisabulkphenomenonandevaporationisasurfacephenomenon

(b) boilingisasurfacephenomenonandevaporationisabulkphenomenon

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(c) boilingandevaporationbotharesurfacephenomenon

(d) boilingandsurfacebotharebulkphenomenon

Ans.(a)boilingisabulkphenomenonandevaporationisasurfacephenomenon

10. Ifthetemperatureofaplaceisincreasethenevaporation:

(a) decrease

(b) increase

(c) remainsame

(d) noneoftheabove

Ans.(b)increase

11. Whichofthefollowinghaveleastinteratomicspacing?

(a) solid

(b) liquid

(c) gases

(d) plasma

Ans.(a)solid

12.If you decrease the surface area and increase the temperature, then the rate of

evaporation

(a) increase

(b) decrease

(c) remainsame

(d) mayincreaseordecreasedependinguponotherfactors

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Ans.(c)remainsame

13. 300kwillhaveitscorrespondingtemperatureindegreecentigradeas:

(a)

(b)

(c)

(d)

Ans.(c)

14. Liquidtogasandgastoliquidchangesarecalled:

(a) vaporizationandcondensation

(b) condensationandvaporization

(c) sublimationandcondensation

(d) condensationandsublimation

Ans.(a)vaporizationandcondensation

15. Physicalstateofwaterat isrespectively

(a) liquid,solidandgas

(b) solid,liquidandgas

(c) solid,gasandliquid

(d) gas,solidandliquid

Ans.(a)liquid,solidandgas

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CBSEClass9Science

ImportantQuestions

Chapter1

MatterinOurSurrounding

3MarksQuestions

1. Adiverisabletocutthroughwaterinaswimmingpool.Whichpropertyofmatter

doesthisobservationshow?

Ans.Ifdiverhasabilitytocutthroughwaterinaswimmingpoolthenitshowsthatthe

particlesofmatterhaveakindofforceworkingbetweenthem.Becauseofthisforcethe

particlesofmatterremaintogethertillsomeexternalforceisapplied.

2. Whatarethecharacteristicsoftheparticlesofmatter?

Ans.Thecharacteristicsofparticlesofmatterareasfollows:

i) particlesofmatterhavegapbetweenthem.

ii) particlesofmatterareincontinuousmotion

iii) particlesofmatterhaveanattractionforcebetweenthemtokeepthemtogether.

3. (a)Tabulatethedifferencesinthecharacteristicsofstatesofmatter.

(b) Commentuponthefollowing:rigidity,compressibility,fluidity,fillingagas

container,shape,kineticenergyanddensity.

Ans.(a)

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(b) Rigidity→Itisthepropertyofmattertomaintainitsshapeevenifexternalforceswork

andthesolidsshowthisproperty.

Compressibility→Itisthepropertyofmattertoallowcompressionunderhighpressureand

thegasesshowthisproperty.

Fluidity→Itisthepropertyofasubstancetoeasilyflowandallowchangeinitsshapeunderexternalforcesandthispropertyisexhibitedbybothliquidsandgases.

Fillingagascontainer→Gasescanbecompressedeasilyhencetheycanbefilledwithina

vesselathighpressure.Thispropertyofgasesallowstheirconvenientfillingintoasmall

containerorcylinderandthatalsoinalargevolume.Italsoallowstheireasytransportfrom

oneplacetotheotheregCNG.

Shape→Accordingtothetypeofmattershapediffersdependinguponlocationofparticles

likeSolidshavedefiniteshapewhileLiquidsacquiretheshapeoftheircontainerandgases

assuchdon’thaveanyshape.

Kineticenergy→Itisthekindofenergypresentinanobjectwhenitisundermotionasthe

particlesofthatobject/matterarecontinuouslymovingthereforematterhaskineticenergy.

Howevergreateristhemovementmorewillbethekineticenergyandviceaversai.e.solid<

liquid<gasDensity→Massperunitvolumeofasubstance/matterisknownasitsdensityi.e.

density=mass/volume.

4. Givereasons

(a) Agasfillscompletelythevesselinwhichitiskept.

(b) Agasexertspressureonthewallsofthecontainer.

(c) Awoodentableshouldbecalledasolid.

(d) Wecaneasilymoveourhandinairbuttodothesamethroughasolidblockofwood

weneedakarateexpert.

Ans.(a)Sincetheattractionforcebetweenparticlesofagasisnegligiblei.e.extremelyless

henceparticlesfreelymove/flowinallpossibledirectionsasaresultgasfillscompletelythe

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vesselinwhichitiskept.

(b) Freelymovingparticlesofgashitthewallsofitscontainercontinuouslyandrandomly

thereforesuchrandomanderraticmotionofgasparticlesexertspressureonthewallsofthe

container.

(c) Awoodentableparticlesarequiterigid,haveafixedlocationandalsopossessadefinite

shapeandvolume.Duetoallthesepropertiesweshouldcallawoodentableasolid

substance.

(d) Airisamixtureofgasesandsinceparticlesofgasarefarapartsosameistrueforair

thereforewecaneasilymoveourhandinair.Butasolidblockofwoodishardandrigidthat

resistsanychangeinlocationofitsparticleshenceweneedakarateexpertincaseofasolid

blockofwood.

5. NameA,B,C,D,EandFinthefollowingdiagramshowingchangeinitsstate.

Ans.A–Fusion(Heating–Melting)

B–Vapourisation

C–Cooling–Condensation(Liquefaction)

D–Cooling–Freezing(Solidification)

E–Sublimation

F–Solidification

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6. Arethethreestateofmatterinter-convertible?Howcantheyinterconnect?

Ans.Yes,threestatesofmatterareinter-convertible.

(a) Solidcanbechangedintoliquidbyboilingandliquidcanbechangedtosolidbycooling

iti.e.bysolidification.

(b) Liquidcanbechangedtogasbyvaporizationbyheatingitandgascanbechangedto

liquidbycondensationi.e.subjectingittolowtemperature.

(c) Solidcanbechangedtogaseousform/statebysublimationandliquidcanbechangedto

solidbycondensation.

7. Howdoesevaporationcausecooling?

Ans.Whenasubstanceevaporatesfromasurface,itabsorbsheatfromthesurfaceand

changeintovapourstate.So,theparticleofliquidabsorbsenergyfromthesurfaceandthe

absorptionofheatfrommakesthesurfacecool.

8. Whyshouldwewearcottonclothesinsummer?

Ans.Duringsummer,weperspiremoreandtheparticlesatthesurfaceoftheliquidgain

energyfromthesurroundingorbodysurfaceandchangeintovapour.Now,cottonbeingan

absorberofwaterhelpsinabsorbingthesweatandexposedittoatmosphereforeasy

evaporationandwefeelcool.

9. Differentiatebetweenphysicalandchemicalchange?

Ans.

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10. Asolutionof islabeled40%.Thedensityofthesolutionis1.3gm/l.whatis

theconcentrationofthesolutionin%(m/v)?

Ans.Concentrationofthesolutionis40%

Thismeansthat

100gmofthesolutioncontains40gofH2So4

Density=

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11. Whatisthestateofinterparticledistanceinsideasolid,liquidandgas?

Ans.Insolids,theparticlesareveryclosetoeachotherandarebondedbystrongforcesof

attractionsointerparticledistanceisleast.Inliquid,theparticlesarefarawayfromeach

otherandarebondedbyweakforcesofattraction,sointerparticledistanceislarge.In

gases,particlesareveryfarapartfromeachotherandarebondedbyveryweakforcesof

attractionso,interparticledistanceisalargest.

12. Whyitisthattosmellcoldfood,wehavetogoclosebutsmellofhotfoodreachesus

severalmetersaway?

Ans.Inhotfood,theparticlesareathightemperaturesoquicklychangestovapourand

hencethevapourshavegreaterkineticenergysotravelfasterandtraveltofaroffdistances.

Whereasincoldfood,becauseoftemperaturebeinglow,particlesdonotchangetovapour

stateandhencecannottravelfastersothesmelldoesnotreachestoapersonsittingfar

away.

13. Whyisitthatawoodenchairshouldbecalledasolidandnotaliquid?

Ans.Awoodenchairshouldbecalledasolidnotaliquidbecausetheparticlesofwooden

chairareveryclosetoeachother,ithasnegligiblecompressibilityanditmaintainsitsshape

whensubjectivetooutsideforce.

14. Giveanexperimenttoshowthatammoniumchlorideundergoessublimation.

Ans.Experimenttoshowthatammoniumchloride undergoessublimation:

(a) Takeaninvertedfunnelandinsideitchinadishwithcrystalofammoniumchloride

.

(b) Heatthecrystalswiththehelpofaburner.

(c) Assoonasthecrystalisheated,weobservethevapoursof andthesolidified

Ammoniumchloride alongthewallsattheupperendofthebeaker.

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(d) Thisshowsthatsolidammoniumchloridedoesnotundergoliquidstatebutdirectly

changestovapourstatewhichthemsolidifiesi.e.itundergoessublimation(solidchanges

directlytogaseswithoutundergoingliquidstate).

15. Whatisdistillationandfractionaldistillation?Whatisthebasicpropertythat

separatesthetwomethods?

Ans.Distillationisusedfortheseparationofcomponentsofamixturecontainingtwo

miscibleliquidthatboilwithoutdecompositionandhavesufficientdifferenceintheir

boilingpoints.Fractionaldistillationisusedfortheseparationofcomponentsofamixture

containingmorethantwomiscibleliquidsforwhichthedifferenceintheirboilingpointsis

lessthan25k.

Thepropertythatseparatesthetwoprocessesisdifferenceintheboilingpointsofthe

componentsofthemixturei.e.ifdifferenceinboilingpointsislargethenweusedistillation

butifdifferenceinboilingpointsisless,weusefractionaldistillation.

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