End Lecture 8. If only the salt s cation affects ph, the solution is acidic. If only the salt s anion affects ph, the solution is basic

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1 End Lecture 8 1 p, the solution is acidic Is Cl acidic or basic in water? 2 Start Lecture 9 Acid Base Reactions Lewis Acid Base AcidBase Properties of Salts Syllabus Learning utcomes 6, 7 Dr. Michael Love (1) p, the solution is acidic p, the solution is acidic Is Cl acidic or basic in water? Cl(aq) (aq) Cl (aq) Answer (a) React anion, Cl, with 2 Cl(aq) (aq) Cl (aq) Answer (b) React cation,, with 2 2 Cl 2 Cl Because Cl is the conjugate base of a very strong acid (Cl), Cl does not affect p. Cl gives a neutral solution, no effect on p acid base base acid is a weak acid, and is a weak base. gives an acidic solution or Ka( ) > Kb(Cl ) so solution is acidic p, the solution is basic 5 p, the solution is basic 6 Calculate the p of 0.10 M a 2 C, K b =2.1 x 10. Calculate the p of 0.10 M a 2 C, K b =2.1 x 10. Answer (a) Cation a 2 neutral (b) Anion C 2 weak base C 2 C Step 1. Set up ICE table for weak base [C ] [C ] [ ] initial change equilib 1

2 p, the solution is basic 7 p, the solution is basic 8 Calculate the p of 0.10 M a 2 C, K b =2.1 x 10. Answer (a) Cation a 2 neutral (b) Anion C 2 weak base C 2 C Step 1. Set up ICE table for weak base [C ] [C ] [ ] initial change x x x equilib 0.10 x x x Calculate the p of 0.10 M a 2 C, K b =2.1 x 10. Step 2. Solve equilibrium expression [C ][ ] x 2 Kb= 2.1x10 = = [C ] 0.10x 100*Kb<0.1, so 0.10x 0.10, giving x= [C ]= [ ]= M p= 2., and p= M a 2 C is a basic solution. If neither the salt s cation nor anion affects p, the solution is neutral, p=7 Is 0.1M acl acidic or basic in water? 9 If neither the salt s cation nor anion affects p, the solution is neutral, p=7 Is 0.1M acl acidic or basic in water? 10 Answer (a) We did a and Cl, before. either a nor Cl affect p (a from a and Cl from Cl). 0.1M acl is neutral in water. If both the salt s cation and anion affect p, the larger of Ka and Kb determine p Is 0.1M Bz acidic or basic in water? 11 If both the salt s cation and anion affect p, the larger of Ka and Kb determine p Is 0.1M Bz acidic or basic in water? Answer Look up Ka( ) and Kb(Bz ) (a) Ka for = 5.6x10 10 (b) Kb for Bz = 1.6x10 10 Ka( ) > Kb(Bz ) 12 Bz makes weakly acidic aqueous solutions. 2

3 Define Lewis acid & Lewis base Lewis acid a substance that accepts an electron pair Lewis base a substance that donates an electron pair B 1 B Lewis acids and bases react B ew bond (Coordinate covalent bond) forms using electron pair from the Lewis base. Geometry changes after reaction (VSEPR model) hydronium ion has a coordinate covalent bond Ammonium ion has a coordinate covalent bond Metal ions form coordinate covalent bonds and complex ions Metal ions form coordinate covalent bonds and complex ions Zn 2 Acid Fe Base Zn 2 Fe Cu 2 Cu As a result, copper ion (a Lewis acid) can react with ammonia (a Lewis base). 2

4 in biology The heme group in hemoglobin interacts with 2 and C. The Fe ion in hemoglobin is a Lewis acid 2 and C can act as Lewis bases C has a strong (irreversible) binding constant with hemoglobin, whereas 2 binds more weakly and reversibly. 19 Many watercontaining complex ions hydrolyze (undergo hydrolysis) to give acidic solutions. [Cu( 2 ) ] 2 2 [Cu( 2 ) ()] 20 ydrolysis makes solutions of Fe, Al, Cu 2, and Pb 2 acidic. 21 Brønsted and Lewis theories explain amphoteric nature of some metal hydroxides. 22 Cu 2 2 bond weakens this bond Cu 2 allowing another 2 to take, (hydrolysis) Al() (s) Al 2 ere Al() is a Brønsted base. Al() (s) Al() ere Al() is a Lewis acid. Al ß Complex ion formation can dissolve a precipitate AgCl(s) Ag Cl K sp = 1.8 x Ag 2 Ag( ) 2 K form = 1.6 x C C 2 is an Acid 1. Electronegativity of atoms takes e, weakening bond. 2. atom in can be taken by 2 to form. 2 AgCl(s) 2 Ag( ) 2 Cl K net = K net = K sp *K form = 2.9x10, so some precipitate dissolves C C =

5 25 Basisity oxoanions as charge 26 C C 2 CCl C 2 Acetic acid Trichloroacetic acid K a = 1.8 x 10 5 K a = 0. C Least basic P Most basic Trichloroacetic acid is stronger than acetic acid because electronegative Cl in CCl stabilizes anion more than the in C. As charge, water interaction, basicity These are both Bronsted and Lewis bases Basisity oxoanions é as #ê 27 Least basic Most basic Cl < Cl 2 < Cl As # oxygens é, strength of acid é, basicity conjugate base ê. Recall that Cl is a strong acid. 5

Required Reading Material.

JF Chemistry 1101 2014-2015 Introduction to Physical Chemistry: Acid Base and Solution Equilibria. Professor Mike Lyons School of Chemistry melyons@tcd.ie Required Reading Material. Kotz, Treichel and