Definition
Whenthevolumetricflaskisusedtoconfiguretheaccurateconcentrationsolution,addwaterwhenthereis1to2cmfromthescaleline,anduseaplasticdroppertosuckwaterintothevolumetricflaskHere,thelineofsightislevelwiththelowestpartofthemeniscustomakeitreachthescribeline.
Anotherexplanation:theconstantvolumeisactuallyastepafterthetransferthroughasmallbeakerandtheglassroddrainage,thatis,whenthetransferredsolutionis2-3cmawayfromthemeniscusofthevolumetricflask,Useaplasticdroppertodropuntilthescalelineistangenttothelowestpointoftheliquidlevel.Thisprocessiscalledconstantvolume.
Theconstantvolumeisgenerallycarriedoutinavolumetricflask.Generally,reagentsarepreparedinabeaker.Forexample,ifa1Lreagentisprepared,itcanbepreparedto450mlto500mlinthebeakerfirst,thentransferredtothevolumetricflask,andfurtheraddedsolvent(Mainlywater),addittotheconcaveliquidsurface2-3cmfromthescaleofthevolumetricflask,letitstandfor1-2minutes,andthenuseaplasticdroppertodripuntilthescalelineistangenttothelowestpointoftheliquidsurface,andcoverthestopper,Flipandshakewell.
Influencingfactors
1.Thelineofsight(lookingup-theamountusedisgreaterthantheactualamount,lookingdown-theamountusedislessthantheactualamount)Thereisamemorableformula:lookingupandlookinghigh,Lookupandlookdown.
2.Whethertheburetteisusedforacidoralkali(whetheritiscleanedafteruse)
3.Observewhethertheburetteneedstobeblown,theburettemarked"Blow"needstobeblown,andtherestdonotneedtobeblown.(Blowthetubethatdoesnotneedtobeblown,theactualliquidaddedismorethanthetheoreticalrequirement,andthetubethatneedstobeblownisnotblown,theactualliquidaddedislessthanthetheoreticalrequirement)
4.WhetherthereisatthelowerendoftheburetteAirbubbles(theamountwilldecreaseifthereisany)
5.Whethertorinseornot(theliquidconcentrationmeterissmallifthereisnorinsing,andtheamountismorethantheactualamount)
6.TurnoverafterconstantvolumeShakewell.Ifthevolumeisconstantafterturningoverandshaking,thesolutionconcentrationwillbetoosmallduetotheaddedwater.
7.Theburetteandvolumetricflaskaremarkedwiththeusetemperature