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How to Make Simple Solutions and Dilutions
Asimpledilutionisoneinwhichaunitvolumeofaliquidmaterialofinterestiscombinedwithanappropriatevolumeofasolventliquidtoachievethedesiredconcentration.Thedilutionfactoristhetotalnumberofunitvolumesinwhichyourmaterialwillbedissolved.Thedilutedmaterialmustthenbethoroughlymixedtoachievethetruedilution.Forexample,a1:5dilution(verbalizeas"1to5"dilution)entailscombining1unitvolumeofdiluent(thematerialtobediluted)+4unitvolumesofthesolventmedium(hence,1+4=5=dilutionfactor). Example:Frozenorangejuiceconcentrateisusuallydilutedin4additionalcansofcoldwater(thedilutionsolvent)givingadilutionfactorof5,i.e.,theorangeconcentraterepresentsoneunitvolumetowhichyouhaveadded4morecans(sameunitvolumes)ofwater.Sotheorangeconcentrateisnowdistributedthrough5unitvolumes.Thiswouldbecalleda1:5dilution,andtheOJisnow1/5asconcentratedasitwasoriginally.So,inasimpledilution,addonelessunitvolumeofsolventthanthedesireddilutionfactorvalue. Topofpage Aserialdilutionissimplyaseriesofsimpledilutionswhichamplifiesthedilutionfactorquicklybeginningwithasmallinitialquantityofmaterial(i.e.,bacterialculture,achemical,orangejuice,etc.).Thesourceofdilutionmaterialforeachstepcomesfromthedilutedmaterialoftheprevious.Inaserialdilutionthetotaldilutionfactoratanypointistheproductoftheindividualdilutionfactorsineachstepuptoit. Example:InthemicroBIOLOGylabinBio201thestudentsperformathreestep1:100serialdilutionofabacterialculture(seefigurebelow).Theinitialstepcombines1unitvolumeculture(10ul)with99unitvolumesofbroth(990ul)=1:100dilution.Inthenextstep,oneunitvolumeofthe1:100dilutioniscombinedwith99unitvolumesofbrothnowyieldingatotaldilutionof1:100x100=1:10,000dilution.Repeatedagain(thethirdstep)thetotaldilutionwouldbe1:100x10,000=1:1,000,000totaldilution.Theconcentrationofbacteriaisnowonemilliontimeslessthanintheoriginalsample. Topofpage Veryoftenyou’llneedtomakeaspecificvolumeofknownconcentrationduetolimitedavailABIlityofliquidmaterials(somechemicalsareveryexpensiveandareonlysoldandusedinsmallquantities,e.g.,micrograms)ortolimittheamountofwaste.Theformulabelowisaquickapproachtocalculatingsuchdilutionswhere: Example1:Supposeyouhave3mlofastocksolutionof100mg/mlampicillin(=C1)andyouwanttomake200ul(=C2)ofsolutionhaving25mg/ml(=V2).Youneedtoknowwhatvolume(V1)ofthestocktouseaspartofthe200ultotalvolumeneeded. V1=thevolumeofstockyou’llstartwith.Thisisyourunknown.C1=100mg/mlinthestocksolutionV2=totalvolumeneededatthenewconcentration=200ul=0.2mlC2=thenewconcentration=25mg/ml Byalgebraicrearrangement: V1=(V2xC2)/C1 V1=(0.2mlx25mg/ml)/100mg/ml andcanceltheunits, =0.05ml =50ul So,youwouldtake0.05ml=50ulofstocksolutionanddiluteitwith150ulofsolventtogetthe200ulof25mg/mlsolutionneeded(rememberthattheamountofsolventusedisbaseduponthefinalvolumeneeded,soyouhavetosubtractthestartingvolumeformthefinaltocalculateit.) Topofpage 4.Molarsolutions(unit=M=moles/L) Sometimesitmaybemoreefficienttousemolaritywhencalculatingconcentrations.A1.0Molar(1.0M)solutionisequivalentto1formulaweight(FW)(g/mole)ofchemicaldissolvedin1liter(1.0L)ofsolvent(usuallywater).Formulaweightisalwaysgivenonthelabelofachemicalbottle(usemolecularweightifitisnotgiven). Example1:Topreparealiterofasimplemolarsolutionfromadryreagent: Multiplytheformulaweight(orMW)bythedesiredmolaritytodeterminehowmanygramsofreagenttouse: Example2:Toprepareaspecificvolumeofaspecificmolarsolutionfromadryreagent: AchemicalhasaFWof180g/moleandyouneed25ml(0.025L)of0.15M(M=moles/L)solution.Howmanygramsofthechemicalmustbedissolvedin25mlwatertomakethissolution? #grams/desiredvolume(L)=desiredmolarity(mole/L)*FW(g/mole) byalgrebraicrearrangement, #grams=desiredvolume(L)*desiredmolarity(mole/L)*FW(g/mole) #grams=0.025L*0.15mole/L*180g/mole aftercancellingtheunits, #grams=0.675g Topofpage 5.PercentSolutions(=partsperhundred) Manyreagentsaremixedaspercentconcentrations.Whenworkingwithadrychemicalitismixedasdrymass(g)pervolumewhere#g/100ml=percentconcentration.A10%solutionisequalto10gdissolvedin100mlofsolvent. Example1:Ifyouwanttomake3%NaClyouwoulddissolve3.0gNaClin100mlwater(ortheequivalentforwhatevervolumeyouneeded). Whenusingliquidreagentsthepercentconcentrationisbaseduponvolumepervolume,i.e.,#ml/100ml. Example2:Ifyouwanttomake70%ethanolyouwouldmix70mlof100%ethanolwith30mlwater(ortheequivalentforwhatevervolumeyouneeded). Toconvertfrom%solutiontomolarity,multiplythepercentsolutionvalueby10togetgrams/L,thendividebytheformulaweight. Example3:Converta6.5%solutionofachemicalwithFW=325.6tomolarity, Toconvertfrommolaritytopercentsolution,multiplythemolaritybytheFWanddivideby10: Example4:Converta0.0045MsolutionofachemicalhavingFW178.7topercentsolution:2.SerialDilution
3.Makingfixedvolumesofspecificconcentrationsfromliquidreagents:
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