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