ch 13. solutions
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Ch 13. Solutions
Chem 30A
Introduction
Chem 30A
Solution
• Solu%on=Homogeneousmixture:Auniformmixtureoftwoormoresubstancesthathasthesamecomposi%onthroughout
• Eg.(Air,seawater,gasoline)
Solutions: Solute and Solvent
• Solute:Substancepresentinthesmalleramount;substancethatisdissolved
• Solvent:Substancepresentinthelargeramount;substanceinwhichanothersubstanceisdissolved
• Eg.Saltwatersolu%on:Saltisthesolute,wateristhesolvent.
Various Types of Solutions
Solubility Depends on Intermolecular Forces
• Solubilitydependsprimarilyonintermolecularforces:Forasolutetobedissolvedinasolvent,solute-solventaFrac%onmustbecomparabletoorgreaterthanthemagnitudesofsolute-soluteorsolvent-solventaFrac%veforces.
“Like Dissolves Like”
• Substanceswithsimilarintermolecularforcesformsolu%onswithoneanother.
• Polarsolventsdissolvepolarsolutesandionicsolutes.
• Nonpolarsolventsdissolvenonpolarsolutes.
Soluble: Polar Solvent + Ionic Solute (Electrolyte Solution)
• PolarsolventmoleculesareaFractedtotheca%onsandanionsofanionicsolid,andhelpbreakuptheionicsolidintoindividualca%onsandanions.
• Ion-dipoleforceHydra%on:Solva%onwithwater
Soluble: Polar Solvent + Polar Solute
• PolarsoluteaFractspolarsolventthroughdipole-dipoleforceand,ifavailable,hydrogenbonding.
Eg.Water+Ethanol(C2H5OH)
Question
• Whyissolidsugarsolubleinwater?
• Whyisacetonesolubleinwater?
Soluble: Nonpolar Solvent + Nonpolar Solute
• NonpolarsoluteaFractsnonpolarsolventthroughLondondispersionforce.
Eg.Fat Hexane
Insoluble: Polar Solvent + Nonpolar Solute
• NonpolarsubstancesdonothavestrongaFrac%ontopolarsubstances.
• Eg.Oilandwatermixture:TherearestrongeraFrac%onsbetweenthewatermoleculesandbetweentheoilmoleculesthanbetweenwaterandoilmolecules.
ExProbs
Solubility • Solubility(quan%ta%ve):Maximumamountofsolute
thatcandissolveinagivenamountofsolventataspecifiedtemperature(eg.SolubilityofNaClis357mg/mlat25°C.)
• Saturatedsolu%on:isatsolubilitylimitatequilibrium(containsmaximumamountofsolutethatcandissolve)
• Unsaturatedsolu%on:isundersolubilitylimit.
• Supersaturatedsolu%on:isoversolubilitylimitforagiventemp.(Occurswhensolu%onissaturatedatahighertempthenallowedtocoolslowly;unstable.)
A Supersaturated Solution
Supersaturatedsodiumacetatesolu%onisdisturbed.
Miscibility
Appliestoliquid-liquidmixtures• Miscible:Twoliquidsdissolveeachotherinallpropor%ons.– Eg.,Ethanolandwater
• Immiscible:Twoliquidsareinsolubleineachother.– Eg.,hexaneandwater
• Par%allymiscible:Twoliquidsdissolveeachotherinlimitedamounts.– Eg.,butanolandwater
Effect of Temperature on Solubility in Water
Thesolubilityofsolidsinwatergenerallyincreaseswithincreasingtemperature.
Solution Concentration Terms
Solution Concentration Terms
1. Masspercent(alsopartspermillionppmandpartsperbillionppb)
2. Molarity
Mass Percent
Masspercent =massofsolute[g]x100 massofsolu%on[g]
*Note:solu%on=solute+solvent
ExProbs
ppm and ppb
ForVERYdilutesolu%ons
Partspermillion(ppm)=massofsolute[g]x106 massofsolu%on[g]
Partsperbillion(ppb)=massofsolute[g]x109
massofsolu%on[g]
ExProbs
Molarity
molarity(M)=molesofsolute__ litersofsolu%on
eg.3MHCl=3molesofHCl 1Lofsolu%on
Read:“3molarHCl”
• Molesofsolute=MxL• L=molesofsolute M
Exprobs
Standard Solution
• Standardsolu%on:Asolu%onwhoseconcentra%onisaccuratelyknown.
• Stepstopreparingastandardsolu%on1. Weighoutasampleofsoluteandtransfertoa
volumetricflask.2. Addsolventandmixtodissolvethesolute.3. Finishaddingsolventtovolumemarkonflaskandmix.
Exprobs
Ion Concentration
5MNaCl• Whatisthemolarconcentra%onofNa+?
• Whatisthemolarconcentra%onofCl–?
5M
5M
Dilution
• Dilu%on:theprocessofaddingwatertoaconcentrated(stock)solu%ontogetasolu%onofdesiredmolarity
Dilution
Conc'd Soln
Diluted Soln
Eg.Prepare500.0mLof0.40MHClfrom10.0MHCl.
0.40M
10.0M
Howmuchstocksolu%onandhowmuchwater?
Dilution
(molesc=molesd)
• Amountofwaterthatneedstobeadded:Vc+Vwater=VdàVwater=Vd-Vc
McxVc=MdxVd
Dilution
Conc'd Soln
Diluted Soln
Molesofsoluteinconc’dsolu%on=molesofsoluteindilutedsolu%on
500mLof0.40Msoln
20mLof10.0Msoln
ExProbs
Osmosis
Osmosis
• Osmosis:thepassageofsolventthroughasemipermeablemembranesepara%ngtwosolu%onsofdifferentconcentra%ons
• Semipermeablemembrane:amembranethatallowssomesubstancestopassthroughbutnotothers
Osmosis
Thenetmovementofsolventisalwaystowardthesolu%onwiththehigherconcentra%on(Solventcanpassthrough;solutecannot).
Osmotic Pressure
Osmo%cpressure:theexcesspressurethatadissolvedsubstanceexertsonthesemipermeablemembrane
Relative Solute Concentrations
• Isotonic:Havingthesamesoluteconcentra%onasanothersolu%on
• Hypertonic:Havingagreatersoluteconcentra%onthananothersolu%on
• Hypotonic:Havingalowersoluteconcentra%onthananothersolu%on
Osmosis Through Red Blood Cell Membrane
CellinIsotonicSolu%on
Cellmembranesaresemipermeable.Cytoplasmhasaconstantsoluteconcentra%on (~0.30osmol).
CellinHypertonicSolu%on
CellinHypotonicSolu%on
H2Omovement
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