Lec Sum14 Ch. 18 Part C Solubility PDF

Preview

Summary

Dr. Schrenk...

Description

Lecture'Summary'14':''Chapter'18'Part'C:'Solubility'&'Complex'Formation'Equilibria'' ' ' Solubility'Equilibria''! ' Photography:!!Salted!paper!printing!is!an!early!photographic!process!where!paper!is!first!floated!on! or!brushed!with!a!solution!of!a!halide!salt!such!as!KCl!and!then!in!the!dark!with!a!solution!of!AgNO3.!! AgCl!is!precipitated!into!the!paper!fiber!structure.!!!(See!the!example!of!Lincoln’s!1861!Inauguration! http://www.loc.gov/pictures/resource/ppmsca.07636/!!)! ! KCl(aq)!+!AgNO3(aq)!!!⇒!!AgCl(s)! O Cl (aq)!+!Ag+!(aq)!!!⇒!!AgCl(s)! !(Net!ionic!equation)! ! In!modern!film!and!photographic!paper!the!silver!halide!is!prepared!in!a!gelatin!layer!that!is!spread! on!a!paper!or!plastic!support.!!The!prepared!paper!or!film!is!exposed!to!light!to!capture!an!image.!! The!image!is!obtained!through!the!photochemical!reduction!of!Ag+!to!Ag!metal.!!! ! To!remove!excess,!unreacted!silver!halide!from!the!paper!or!gelatin!it!must!be!made!soluble.!!This! has!been!accomplished!since!almost!the!beginning!of!photography!through!use!of!!"fixer"!sodium! thiosulfate!(Na2S2O3).! AgCl(s)!+!2!S2O32O(aq)!⇔![Ag(S2O3)!2]3O!(aq)!+!!ClO!(aq)! ! (Net!ionic!equation)! ! (Note:!actually!a!variety!of!complexes!are!formed!between!Ag+!and!thiosulfate!–!reality!is!often!a!little! more!complicated)! ! Photographic!processes!rely!on!solubility!and!precipitation!governed!by!solubility'equilibria'(Ksp)! as!well!as!complex'formation'equilibria'(Kf'or'β β in!earlier!literature).! ! Ksp''is'the'solubility'product!equilibria!constant!which!is!defined!for!the!reaction!of!putting!a!ionic! solid!into!solution.!! !i.e.,!AgCl(s)!!!⇔!!!Ag+!(aq)!!!+!!!!ClO!(aq)! ! Kf'(or'sometimes'β β )'is'the'complex'formation!equilibria!constant!which!is!defined!for!the!reaction!of! forming!a!complex!usually!of!a!transition!metal.!i.e.,!Ag+!(aq)+!2!S2O32O!(aq)⇔ ![Ag(S2O3)!2]3O!(aq)! ! The'ideas'and'processes'you’ve'used'for'gas'phase'equilibria'and'acidIbase'equilibria'apply'here.' ' + Consider'the'solubility'of'AgCl.!!What!is!the!concentration!of!Ag !in!a!saturated!solution!(i.e.,!there! is!solid!present)?!!Remember,!solids!like!solvents!do!not!appear!in!equilibrium!expressions.! ! ! ! AgCl(s)!!!!⇔!!!! Ag+!(aq)!!!+!!!!ClO(aq)! ! ! Initial! ! solid! ! !!!0! !!!!!!!0! Change! ! OOOOOO! ! !+x! !!!!!!+x! Equilibrium!! OOOOOO! ! !+x! !!!!!!+x! ! ! !! x=![Ag+]!=![!ClO]=!1.3!x!10O5 M! Ksp!!=![Ag+][!ClO]!=!(x)(x)!=!1.6!x!10O10 ! ! S=Molar!solubility!is!also!1.3!x!10O5 M.!!This!is!the!maximum!concentration!of!AgCl!that!can!exist!in!solution! before!precipitation!will!occur.! ! ! ! ! ! ! !! ! Detour:'!If'you'know'you'can'dissolve'up'to'6.5'x'10I5 moles'per'liter'of'Ag2Cr2O7'what'is'Ksp'for' ! Ag2Cr2O7?'!(S!=!molar!solubility!=!6.5!x!10I5 M)! ! ! Ag2Cr2O7!(s)!⇔!!!2!Ag+!(aq)!!+!Cr2O72I(aq)! ! !

From!stoichiometry:!![Cr2O72I]!=!S!=!6.5!x!10I5!M!and![Ag+]!=!2S!=!2(6.5!x!10I5!M)! ! ! Ksp!=!![Ag+]2![Cr2O72I]!=!(2S) 2!(S)!=!4S3!=!4(6.5!x!10I5!M)'3! ! Ksp!=!1.1!x!10I12!

! ! ' What'if'you'add'0.010'moles'NaCl'to'1'liter'of'the'AgCl'system'described'above?' ! ! ! AgCl(s)!!!!!⇔!!!Ag+!(aq)!!!!!!+!!!!ClO(aq)! ! ! initial! ! OOOOO! !!!!!!!!!!0!! !!!!!!!!!!!0.010!M!!!!!(0.010!moles!in!1!liter!of!solution)! change! ! ! !!!!!!!!+x! ! +x! equilibrium! ! ! !!!!!!!!!!x! !!!!!!!!!!!0.010!+x! ! Assume!x...