159_lecture_19_ksp_thermo_home-77

159_lecture_19_ksp_thermo_home-77 - 4/2/2008 Lecture 19 Ksp...

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4/2/2008 1 All rights reserved G. Hall 1 Lecture 19 K sp and Entropy All rights reserved G. Hall 2 Outline Lecture 19 L Continue solubility products and common ions. L How soluble is a solid in water? L Summary of Chapter 19. L Thermodynamics « Entropy
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4/2/2008 2 All rights reserved G. Hall 3 Writing K sp L aA + bB = cC + dD L Again, balance equation very important. L Call this K sp K eq = [ ] [ ] [ ] [ ] C D A B c d a b All rights reserved G. Hall 4 Definition of K sp L for HgCl 2 (s) = Hg + (aq) + 2Cl - (aq) L K sp = [Hg + ] [Cl - ] 2 L equation says that when the product of the two ions are greater than or equal to K sp , a precipitate will form.
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4/2/2008 3 5 Table 19.3 Relationship Between K sp and Solubility at 25 0 C No. of Ions Formula Cation:Anion K sp Solubility (M) 2 MgCO 3 1:1 3.5 x 10 -8 1.9 x 10 -4 2 PbSO 4 1:1 1.6 x 10 -8 1.3 x 10 -4 2 BaCrO 4 1:1 2.1 x 10 -10 1.4 x 10 -5 3 Ca(OH) 2 1:2 5.5 x 10 -6 1.2 x 10 -2 3 BaF 2 1:2 1.5 x 10 -6 7.2 x 10 -3 3 CaF 2 1:2 3.2 x 10 -11 2.0 x 10 -4 3 Ag 2 CrO 4 2:1 2.6 x 10 -12 8.7 x 10 -5 Try to show that these solubilities are correct. All rights reserved G. Hall 6 Sample Problem 19.4 Writing Ion-Product Expressions for Slightly Soluble Ionic Compounds SOLUTION: PROBLEM: Write the ion-product expression for each of the following: (a) Magnesium carbonate (b) Iron (II) hydroxide (c) Calcium phosphate (d) Silver sulfide PLAN: Write an equation which describes a saturated solution. Take note of the sulfide ion produced in part (d). K sp = [Mg 2+ ][CO 3 2- ] (a) MgCO 3 ( s ) Mg 2+ ( aq ) + CO 3 2- ( aq ) K sp = [Fe 2+ ][OH - ] 2 (b) Fe(OH) 2 ( s ) Fe 2+ ( aq ) + 2OH - ( aq ) K sp = [Ca 2+ ] 3 [PO 4 3- ] 2 (c) Ca 3 (PO 4 ) 2 ( s ) 3Ca 2+ ( aq ) + 2PO 4 3- ( aq ) (d) Ag 2 S( s ) 2Ag + ( aq ) + S 2- ( aq ) S 2- ( aq ) + H 2 O( l ) HS - ( aq ) + OH - ( aq ) Ag 2 S( s ) + H 2 O( l ) 2Ag + ( aq ) + HS - ( aq ) + OH - ( aq ) K sp = [Ag + ] 2 [HS - ][OH - ]
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4 All rights reserved G. Hall 7 How soluble in water? L How soluble is AgCl in water at STP? L Set up equations: L AgCl(s) = Ag + (aq) + Cl - (aq) L let x = solubility of AgCl(s) then set up table: L AgCl(s) = Ag + (aq) + Cl - (aq) L Start x 0 0 L Change -x x x L Equil 0 x x L K sp =[x][x] = 1E-12; x=1E-6 M (watch units) All rights reserved G. Hall 8 How much is soluble in water? L
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This note was uploaded on 04/03/2008 for the course CHEM 159-160 taught by Professor Zbaida during the Fall '07 term at Rutgers.

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159_lecture_19_ksp_thermo_home-77 - 4/2/2008 Lecture 19 Ksp...

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