Lab2

Determinationofindoorformaldehydeby

spectrophotometer

Name:XuFeiGroup:The3rdgroup

Date:Oct.11st2012

Part1Theintroduction

1.1Thepurposes

(1)Learnhowtooperatethespectrophotometer;

(2)Learntheprinciplesandproceduresofthestandardmethodtoquantifyindoorformaldehyde;

(3)Learnthequantificationmethodbyspectrophotometerandthedatatreatment.

1.2Theprinciples

Thebasicoperatingprincipleofspectrophotometerisbasedonthemeasurementoflightabsorptionduetoelectronictransitionsinasample.BasedonBeer’slaw,theabsorbance,A,isrelatedtotheincidentlightintensity,I0,andtransmittedlightintensity,I,concentrationofasolutionsample,c,pathlengthofthesample,l,absorptioncoefficient,α,andmolarabsorptivity,ε,bythefollowingequation:A=logI0/I=εlc=αc.Inanexperiment,bothI0andIcanbemeasuredandthusAcanbedeterminedexperimentally.Aisdirectlyproportionaltotheconcentrationoftheanalyteabsorbedfortheexistingsetofconditions.Theconcentrationisusuallydeterminedfromacalibrationcurve,obtainedusingstandardsofknownconcentration.

Part2Thematerialsandapparatus

Spectrophotometer,absorptiontubewithlargebubbler(outletdiameter1mm,distancebetweenoutletandbottom≤5mm);constant-currentsampler(flowrange0m3/min~1m3/min);colorimetriccylinderwithstopper(10ml).

Part3Theprocedure

3.1Standardizationoftheformaldehydestockstandardsolution

20.00mLformaldehydestockstandardsolutionisaddedintoaglass-stoppedbottle(250mL).20.00mLofiodinesolutionand15mLof1mol/Lsodiumhydroxidesolutionareaddedandthemixtureisallowedtostandfor15min,20mLof0.5mol/Lsulfuricacidsolutionisaddedandthesolutionisallowedtostandforanother15min.Thesolutioniscalibratedbytitratingwithsodiumthiosulfatestandardsolutionuntilthesolutionisyellow.1mLof5%starchsolutionisaddedandthetitrationiscontinueduntilbluefades.ThevolumeofsodiumthiosulfatestandardsolutionconsumedisrecordedasV2(mL).TitratetheblanksampleofwaterandrecordtheconsumptionvolumeofsodiumthiosulfatestandardsolutionasV1(mL).Thecontentofformaldehydeiscalculatedbytheformulabelow.

Where:cconcentrationofformaldehyde(mg/mL);

V1volumeofthesodiumthiosulfatestandardsolutionconsumedfortheblank(mL);

V2volumeofthesodiumthiosulfatestandardsolutionconsumedforformaldehydestockstandardsolution(mL);

Nnormalityofsodiumthiosulfatestandardsolution;

15equivalentmassofformaldehyde;

20volumeoftheformaldehydestockstandardsolution(mL).

3.2Formaldehydestandardsolution

Formaldehydestockstandardsolutionisdilutedto10μg/mLformaldehydewithwater.10.00mLofthissolutionand5mLofstockabsorptionsolutionareaddedtoavolumetricflask(100mL)anddilutedtothemarkwithwater.Theformaldehydestandardsolutionisready30minlater.Itcontains1.00μgofformaldehydepermilliliter(mL)andisstablefor24h.

3.3Samplecollection

Place5mlofabsorptionsolutionintoalargebubblerabsorptiontubandsampleairataflowrateof0.5m3/minuntil10m3ofairahspassedthroughtheabsorptionsolution.Recordthetemperatureandatmosphericpressureofthesamplingsite.Thesampleshouldbeanalyzedatroomtemperaturewithin24hofsampling.

3.4Analysisprocedure

(1)Plottingofstandardcurve

Standardsolutionsarepreparedin9volumetricflasks(10ml)accordingtothetablebelow:

Table1.Dataforstandardcurve

NO.

0

1

2

3

4

5

6

7

8

Formaldehyde

standard

solution(ml)

0

0.10

0.20

0.40

0.60

0.80

1.00

1.50

2.00

Absorption

solution(ml)

5.0

4.9

4.8

4.6

4.4

4.2

4.0

3.5

3.0

Contentofformaldehyde(μg)

0

0.1

0.2

0.4

0.6

0.8

1.0

1.5

2.0

Toeachofthecolorimetriccylindersadded0.4mlof1%ammoniumferricsulfatesolutionandallowtostandfor15min.theabsorbanceismeasuredat630nmusinga1cmcuvetteandwaterasthereference.Astandardvurveisplottedusingcontentofformaldehydeasabscissaandabsorbanceasordinate.Theslopeofthestandardcurveiscalculated.ThecalculationfactorBg(μg/absorbance)isequaltoreciprocaloftheslope.

(2)Determinationofformaldehydeinsamples

Aftersampling,thesamplesolutionistransferredintoacolorimetriccylinder.Theabsorptiontubeiswashedwithasmallamountofabsorptionsolutionuntilthetotalvolumeis5ml.Theabsorbanceismeasuredaccordingtothesameprocedureasforthestandardcurve.TheabsorbanceoftheabsorptionsolutionblankismeasuredandrecordedasA0.

Part4Theresults

4.1Therawdata

TherawdataisV1=20.10mL

,V2=

6.85mL

Theabsorbancevaluesofsample:0.155and0.148

AccordingtoV1=20.10mLandV2=6.85mLandtheformula

,

theconcentrationoftheformaldehydestockstandardsolutionis:

0.994mg/ml

No.

1

2

3

4

5

concentration（mg/ml）

0.10

0.40

0.80

1.00

1.50

Abs1

0.044

0.102

0.179

0.224

0.318

Abs2

0.040

0.104

0.188

0.224

0.331

4.2Thestandardcurve

Accordingtotherawdata,wecangettheabsorbancevaluesandmakethestandardcurve.

No.

1

2

3

4

5

concentration（mg/ml）

0.10

0.40

0.80

1.00

1.50

Abs1

0.044

0.102

0.179

0.224

0.318

Abs2

0.040

0.104

0.188

0.224

0.331

Meanoftheabsorbancevalues

0.042

0.103

0.1835

0.224

0.3245

4.3Calculation

Lookingatthestandardcurve,weknowthatthelinearformulaisy=0.2017x+0.0221.Theabsorbancevaluesofsampleare0.155and0.148.Itmeanstheabsorbancevaluesofsampleis0.155,namely,theyis0.155.

Thenput0.155intoy=0.2017x+0.0221,wecandrawx=0.659μg/ml

Namely,theconcentrationofanothersampleis0.624μg/ml

Sotheconcentrationofthesample:

c=(c1+c2)/2=(0.659+0.624)/2=0.6415μg/ml

Part5Discussion

Thisexperimentisthedeterminationofindoorformaldehydebyspectrophotometer,Ilearnhowtocollectsamples,howtostandardizetheformaldehydestockstandardsolution,howtoplotoutthestandardcurveandhowtooperatethespectrophotometer.Intheprocessoftitration,weobservethanthecolorofsolutiongraduallybecomesyellow,blueafter5%starchsolutionaddedandcolorless.Intheexperiment,themostimportantthingisteamwork.

Duringtheexperiment,ourteamhadthreesections,thefirstpartisthedeterminationofthevolumeofthesodiumthiosulfatestandardsolutionconsumedforformaldehydestockstandardsolution,thesecondpartisdetermi