液体表面张力的测定Determination of surface tension of liquidsWord格式文档下载.docx

液体表面张力的测定Determination of surface tension of liquidsWord格式文档下载.docx

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Theattractionofgasmoleculesoutsidetheliquid,andtheactionoftheformerisgreaterthanthatofthelatter.Therefore,onthesurfacelayerofliquidsurface

Eachmoleculeissubjectedtoanunbalancedforcethatisperpendiculartoanddirectedtowardtheinterioroftheliquid.Thisappealisapparentonthesurface

Themoleculespushinwardtomakeupthesmallestareaoftheliquid.Toincreasethesurfaceareaofaliquid,itisnecessarytohaveresistance

Todowork,increasethepotentialenergyofmolecules.Therefore,moleculesarelargerinthesurfacelayerthanintheliquid

Potentialenergy,whichissurfacefreeenergy,usuallyincreasesthemaximumworkrequiredbythesurfaceofasquaremeterbyAorincreases

Gchangeofsurfacefreeenergybyasquaremeters,knownasthesurfaceunitsurfaceenergy,anditsunitisJ-m-1;

Theforceactingonthesurfaceofaliquidandtheunitinitslengththatisusedtoshrinkitiscalledsurfacetension

Force,whoseunitisN.M-1.Thesurfaceenergyofaunitsurfaceofaliquidisequaltoitssurfacetension.

IfthesurfaceareaoftheliquidisincreasedbyS,thereversibleworkAshallbe:

-A=G=gammaS

（1）

Thesurfacetensionofliquidisrelatedtotemperature.Thehigherthetemperatureis,thesmallerthesurfacetensionis.Atthecriticaltemperature,

Liquidsandgasesaredivided,andsurfacetensionapproacheszero.Thesurfacetensionofaliquidisalsorelatedtothepurityoftheliquid

Inapureliquid（solvent）,iftheimpurity（solute）isadded,thesurfacetensionchanges

Smalldependsonthenatureofthesoluteandtheamountadded.

Forpuresolvents,thesurfacelayeristhesameastheinternal,butnotthesolution.When

Whenthesoluteisadded,thesurfacetensionofthesolventchanges.Accordingtotheprincipleofminimumenergy,ifthesolutecandissolve

Thesurfacetensionoftheagentisthatthesoluteconcentrationinthesurfacelayershouldbegreaterthantheconcentrationinthesolution,iftheaddedsolutecan

Ifthesurfacetensionofthesolventisraised,thentheconcentrationofthesoluteinthesurfacelayershouldbelowerthantheconcentrationinsidethesolution.this

Thephenomenonthatthesurfaceconcentrationisdifferentfromtheconcentrationofthesolutioniscalledsurfaceadsorptionofthesolution.Atacertaintemperatureandpressure

Force,

Thesurfacetensionofsolutionandtheamountofadsorbedsolutesolutionandaddingthesolutionquality（i.e.concentration）

TherelationshipbetweenthembyGibbs（Gibbs）said:

Type:

fortheadsorptionofmol.m（gamma

TheconcentrationofR（mol.L-1）;

Isthegasconstant

Thechangeofsurfacetensiontemperaturechangewithsolutionconcentrationrate（

Gamma?

/?

C）T<

0,>

0,gammasurfacelayer,theconcentrationisgreaterthantheconcentrationoftheinternalsolution

Effect。

Ifgammawithincreasingconcentrationofthe

Thedegreeofconcentrationislessthanthesolutionitself,

TheadsorptionofsolutesandconcentrationofC

C/gammamap,astraightline,

IfthemolecularNrepresents1m2surfacesolutenumber

WhereLisAvogadroconstant

From

（2）canbeseen,aslongastheconcentrationanddeterminationofsurfacetensionofsolution

Theadsorptionamountofgammasolution.

Inthisexperiment,themeasurementoftheconcentrationofsolutionisthecorrespondencebetweentheapplicationconcentrationandrefractiveindex

Isanapplicationofthemaximumbubblepressure

Tutu

chart

One

1.1.

1..

Beaker

Beaker;

;

2.;

2.2.

Figure2.2-1

Isaschematicdiagramofapparatusformeasuringsurfacetensionofthemaximumbubblepressuremethod

Installedinthebranchtube5,thecapillary

Gamma=-（（T）

（mol.m-1）;

gammasurfacetension（J,m-1）;

T

Absolutetemperature

Isthegasconstant（8.314J.K-1-mol-1）.（

Cchangeofsurfacetensiontemperaturechangewithsolutionconcentrationrate.Ifgammadecreaseswiththeincreaseoftheconcentrationof

Theconcentrationofsurfacelayerisgreaterthantheconcentrationoftheinternalsolution

Withtheincreasingconcentration（i.e.

C）T>

0,<

0,gammasurfacelayer,thesolutionconcentration

Thatiscallednegativeadsorption.

TherelationshipbetweenCwithLangumuirisothermaladsorptionequation

C

Gamma

The

Gamma-

Gamma-K

Thus,theslopeofthelineandtheinterceptcanbeobtainedbyconstantKandgamma

Thenumberofsolutemoleculesonthesurface,then:

N=gamma-L

Thiscanbeaconstant,eachmoleculeinthecross-sectionalareaoccupiedbythesurface

Gamma-Am=1/

Aslongasthedeterminationofthesolutionconcentrationandthesurfacetensioncanbeobtainedunderdifferentconcentrations

Themeasurementoftheconcentrationofsolutionisthecorrespondencebetweentheapplicationconcentrationandrefractiveindex,

Isthemaximumbubblepressuremethod.

Figure2

Twenty-two

2-

-

-1

Eleven

Maximum

Thebiggest

Determinationofsurfacetensionofbubblemethodapparatus

Determinationofsurfacetensiondeviceofbubblemethoddeterminationofsurfacetensionofbubblemethodequipment

Two

2.dropfunnel

Thedroppingfunneldropfunnel

Dropfunnel;

3.;

3.3.

Differentialpressuremeasuringinstrument3.digitalmicro

Digitalmicrodifferentialpressuremeasuringinstrumentdigitalmicrodifferentialpressuremeasuringinstrument

Differentialpressuremeasuringinstrumentdigitalmicro;

4.;

4.4.

4.thermostat

Thermostatthermostat

Thermostaticdevice;

Five

5.5.

5.withabranchtube

Withabranchtubewithbranchtube

Testtubewithbranchpipe;

6.;

6.6.

6.capillary

Capillarycapillary

capillary

Isthemaximumbubblepressuremethodofmeasuringsurfacetensiondevicediagram

.Aliquidthatwilltestsurfacetension

Theendsurfaceofthecapillary6istangenttotheliquidsurfaceandtheliquidsurfacerisesalongthecapillarytube

（2）

Forabsolutetemperature（K）andCforC）,Tmeans

Decreasewiththeincreaseofconcentration

Atthispoint,theconcentrationofthesolutionsurfacelayerisgreaterthantheconcentrationinsidethesolution,whichiscalledpositiveadsorption

Theconcentrationofthesolutionsurfacelayeratthistime

Isothermaladsorptionequationrepresentation:

Gammainfinity.

Thus,thesectionalareaoccupiedbyeachmoleculeonthesurfaceisAm:

Itcanbeobtainedatvariousconcentrations

Measurementofsurfacetension

Aliquidthatwilltestsurfacetension

Theliquidsurfacerisesalongthecapillaryandopensthedropfunnel.2ofthepistonslowlydrawsair,becausethepressureontheliquidlevelinthecapillary（Patmosphere）atthistime

Itislargerthanthepressureonthesurfaceofthetubeinthetesttube（Psystem）,sotheliquidlevelinthecapillarygraduallydrops,andthebubbleslowlyescapesfromthecapillarytubeend.Duringtheformationofbubbles,theconcavesurfaceisproducedbecauseofthesurfacetension

AnadditionalpressurePispointedouttotheoutsideoftheliquidlevel,sothereisthefollowingrelationship:

Patmosphere=Psystem+deltaP

P=P,theatmosphericPsystem（3）additionalpressurePisproportionaltothesurfacetensionofthesolution,andisinverselyproportionaltotheradiusofcurvatureofthebubbleR

Tietype

P=2,gamma/R（4）

Ifthediameterofthecapillaryissmall,thebubblesformedcanbeconsideredspherical.Whenbubblesareformedjustbecauseofthesurface

Almostflat,sotheradiusofcurvatureisverylarge.Whenthebubbleishemispherical,theradiusofcurvatureisequaltocapillary

Thetubediameterisr,andtheRvalueisminimumatthistime.Asthebubbleincreasesfurther,itincreasesonly（seeFigure2）,

Untiltheliquidlevelescapes.Accordingto（4）,whenR=R,theadditionalpressureisthemaximum

P=2,gamma/r（5）

Thismaximumadditionalpressurecanbereadonthedigitalmicropressuredifferentialmeter.

-2

Fig.2Schematicofbubbleformation

Schematicdiagramofbubbleformation

Intheexperiment,theRisaconstantifthesamecapillaryandmanometerareused.Ifknown

Surfacetensionofliquidasastandard,aftertheexperimentmeasureditsdeltaP,youcanfindR.Thenjustusethisone

Thepvalueofotherliquidscanbemeasuredbytheinstrument.Thesurfacetensionofvariousliquidsca