molecular chap 2 solution preparation pdf.pdf

about solution preparation tecniques

1. Solution Preparation
Lecture 2

2. Objectives:
After completion of this chapter, the student will be able to;
Define different terminologies related to reagent and chemicals
Recognize different methods of expressing strength of solution
Carry out different calculations and prepare different solutions

3. Definitions of terms:
Solution:isahomogenousmixtureoftwoormorecomponentsthatcanbe
variedincompositionwithincertainlimit.
Everysolutionconsistsoftwoparts,thesolventandsolute
Solvent:isthesubstancethatdissolvesthesolute.Thesolventinmostcases
areliquid.
Liquidsolventaredividedintotwo:-
•Polarsolvents:likewater,alcohol
•Non-polarsolvent:likechloroform,benzene,ether

4. Solute:isthesubstancethatisdissolvedinsolvent.Itcanbesolids,liquidor
gases.
Ifasolidorgasismixedwithaliquid,theliquidisconsideredassolvent.
Ifthesolutionisamixtureoftwoliquid,thecomponentpresentinlarge
amountisconsideredasthesolvent.

5. Stockreagentsolution
Itisaconcentratedreagentsolutionwhichisdilutedtoprepareaworking
solution
Ithasalongershelflifeandoccupieslessspaceinstoragethantheworking
solution
Workingreagentsolution
Canbedilutedfromthestocksolutionorprepareddirectlyfromthereagent
chemicalfollowingtherecommendedprocedures

6. Types of solution
1.SolidSolution:aremixturesoftwoormoresolidsandtheyaredispersedor
mixedrandomlythroughoutoneanotherresultingaheterogeneousmixture.
E.g.Alloys
2.GaseousSolution:isahomogeneousmixtureoftwoormoregases
E.g.AirisasolutionofO
2,N2,H
2,CO
2andothergases.
3.LiquidSolution:isasolutionwherethesolventandthesoluteareliquid.
But,thesolutecanalsobesolidorgas.

7. MakingaSolution:WhatYouNeedtoKnow
Whichisbeingdissolved/Solute
Whichisbeingusedtodissolvethesolute/Solvent
Thedesiredconcentration
Thedesiredvolume

8. Expression of the strength of solution
Expressionofthestrengthofsolutionsisbroadlydividedintotwo
1.Relativeexpressionsoftheconcentration
2.Quantitativeexpressionoftheconcentration.
1.Relativeexpressionsoftheconcentrations
a.DilutedSolution:smallamountofsolutedissolvedinlargeamountof
solvent.Example;1%H
2SO
4
b.ConcentratedSolution:largeamountofsolutedissolvedinasmall
amountofsolvent.Example;98%H
2SO
4

9. c.SaturatedSolution:Agivenvolumeofsolventhasdissolvedallthesolute
underagivenconditionoftemperatureandpressure.
Solutethatdissolvesuntilitisunabletodissolveanymore
d.Suppersaturatedsolutions:isasolutionwhichholdsmoresolutethanit
canholdnormallyatagiventemperatureandpressure.
contains more undissolved solute than the saturated solution
because of its tendency to crystallize and precipitate.

10. 2. Quantitative expressions of concentration of solution
Theconcentrationofsolutesinasolutioncanbeexpressedquantitativelyin
physicalunitsorchemicalunits.
A.Physicalunit:
•Percentages
•Partsperunit
•Density(mass/volume)
•Specificgravity
B.Chemicalunits.
•Mole
•Equivalents
•Molarity
•Normality
•Molality

11. 1. Percentage
A.Percentageweightbyweight(%w/w):
Itisthenumberofpartsofsolutebyweightper100partssolutionby
weight.
Example;37gm%w/wHCl=meanseach100gmofHClsolutioncontain
37gmofHCLandtherest63gmsolvent(water)
B.Percentageweightbyvolume(%w/v):
Itisthenumberofpartsofsolutebyweightper100partsofsolutionby
volume.
Example;98gm%w/vglucosesolutionmeans,98gmglucosewas
dissolvedin100mlsolution.

12. C.Percentagevolumebyvolume(%V/V):
Itisthenumberofpartsofsolutebyvolumeper100partsofsolvent
Example:-70%V/Vethanolmeans,70mlofethanolwasmixedwith30ml
ofwater
Problem 1
Howcanwepreparedthefollowingsolutions?
a)100mLof40%(w/v)polyethyleneglycol(PEG)
b)47mLofa7%(w/v)solutionofsodiumchloride
c)200mLofa95%(v/v)solutionofethanol

13. 2.Partsperunit
Thisistoexpressthenumberofpartsbyvolumeorbyweightofsolute
pergivenvolumeorweightofthesolution.
•Example:-If1mlethanol(pure)isdilutedwith999mlofwater,to
expressthenumberofpartsofethanol,Itcanbesaidthatethanol
solutionis1:1000
3.Dilutionofsolution
Dilutionistheprocessbywhichtheconcentrationofagivensolutionis
decreasedbytheadditionofsolvent.

14. Adilutionrepresentstheratiooftheconcentratedorstockmaterialof
thefinalvolumeofasolution.
Simpledilution
Ageneralprocessofpreparinglessconcentrationsolutionsfroma
solutionofgreaterconcentration.
Serialdilution
Itisdefinedasmultipleprogressivedilutionsrangingfrommore
concentratedsolutionstolessconcentratedsolutions

15. Dilutionisusedtoprepare
Workingsolutionfromstocksolution
Measurableconcentrationofasample
Wheneverasolutionisdiluted,itsvolumeisincreasedanditsconcentration
decreased,butthetotalamountofsoluteremainsunchanged.
Thefollowingequationisusedtodeterminethevolume(V2)neededtodilutea
givenvolumeof(V1)ofsolutionofknownconcentration(C1)tothedesired
lesserconcentration(C2).
C1 x V1 = C2 x V2

16. UsingDilutions,MolarorNormaltoMakeComplexSolutions
Solutionsoftenhavemorethanjustonesolute.
Tomakecomplexsolutionsfromtwoormoresolidsolutesormultipleliquid
stocksolutionsby:
→Treatingeachdilutionindividually
→Combinethemtogetherinonecontainerand
→Bringsthevolumeuptoyourinterest

17. Problem2:If30mLof70%ethanolistobepreparedfroma95%ethanolstock
solution,howmanymlofstockisneeded?
Problem3:If8mLofdistilledwaterareaddedto2mLof95%ethanol,whatis
theconcentrationofthedilutedethanolsolution?
Problem4:Supposeyouwanttomake100mlofa1XTriton-Xsolutionusinga
100XTriton-Xstocksolution.Howwouldyoudoit?
Problem5:
•Howtoprepare1:100dilutionofacidalcoholsolution.
•Howtoprepare1:4acidalcoholsolution,phenol\chloroform(50:50)
•Howtoprepare1:10serialdilutionofsoil/watersampleforabacterialculture.

18. B.Concentrationofsolutioninchemicalunits
Commonlyusedchemicalunittoexpressthequantityofsolutesinagiven
solutionare:-Mole,Equivalent,Molarity,NormalityandMolality
1.Mole
1moleofagivensubstanceisitsatomicweightormolecularweight
expressedingram
Example:-1mole=6.02x10
23
particleofsubstance
1moleofNa=23grams=6.02x10
23
1moleofglucose(C
6H
12O
6)=180gm,Since,atomicweightof
C=12,H=1,O=16

19. 2.Molarsolution(Molarity=M)
Itisthesolutionswhichcontains1moleofthesoluteperlitterofsolution.
SimpleformulatocalculateMorality
Molarity(M)=MoleofsoluteORActualmassingram
Vol.(L) Mol.wtxVol(L)
Example-1:Howdoyouprepare100mlof1molarNaOHsolution.
MolwtofNaOH=40gm/mol

20. Problems
Preparethefollowingmolarsolutions
1.Prepare50mlof0.5MNaClsolution
2.Howtoprepare100mlof0.5MHClsolution.

21. 3.Normalsolution(Normality=N)
Itisthenumberofequivalentofsolutesthatarepresentinoneliterofsolution.
N=noofequivalentingram(solute)/V(l)
noofequivalent=Massingram/Equivalentweight
Equivalentweight=Molecularweight/noofH(OH)ions
So,
Normality(N)=ActualMassingrams
EquivalentweightxVol.inliter

22. If1gmequivalentH
2SO4isdissolvedinoneliterofsolutionitiscalledNormal
solutionofH
2SO4or1NH
2SO4.
N.B.Oneequivalentofsubstanceisitsequivalentweightexpressedingrams.
Weighttobedissolved=equivalentweightxVol.inLxNormality.
Example-1:WhatisthenormalityofKOH.If5.6gmKOHisdissolvedin1liter
ofsolution?
Solution
Actual mass = 5.6gm, N= Actual Mass in gram= 5.6gm= 0.1N KOH
Volume = 1L , Equ. Wtx vol in lit 56 x 1L

23. Problems:
1.Prepare100mlof0.2NNaOHsolution.
2.Prepare100mlof1NHClsolution

24. Thank you