Lewis Bases - University of Michigan

1 1E5 Lewis Acids and Bases (Session 1)November 5 - 11E5 Lewis Acids and Bases (Session 1)November 5 - 11 Session oneSession one Pre-lab ( ) duePre-lab ( ) due 1st hour discussion of E41st hour discussion of E4 Lab (Parts 1andLab (Parts 1and 2A)2A)Session two Lab: Parts 2B, 3 and 4 AcidsAcids Bronsted: Acids are proton Problem Compounds containing cations other thanH+ are acids!Problem: Some acids do not contain protonsProblem: Some acids do not contain protonsExample: Al3+ (aq) = pH 3!Deodorants and acid loving plant foods containaluminum saltsLewis Acids and BasesLewis Acids and Bases A base DONATES unbonded ELECTRON PAIR/S. An acid ACCEPTS ELECTRON PAIR/S . acid base base acid HCl-H + O HCl- H H + O HDefines acid / base without using the word proton: Lewis AcidsLewis Acids Electron deficient species ; potential electronpair acceptors.

2 Lewis acids: H+ Cu2+ Al3+ I m deficient! AcidLewis BasesLewis Bases Electron rich species; electron pair donors.(ammine)(hydroxo)(aquo)Ammonia hydroxide ion water__2 Lewis acid - base ReactionsLewis acid - base Reactions The acid reacts with the base by bonding to oneor more available electron pairs on the base . acid + base Complex ion H H+ + O H H H + O HExample The acid - base bond is coordinate covalent. The product is a complex or complex ionLewis acid - base ReactionsLewis acid - base ReactionsMetal ionsurroundedby watermoleculesMetal ionBONDEDto watermoleculesLewis acid - base Reaction ProductsLewis acid - base Reaction ProductsNet Reaction Examples Ni2+ + 6 H2O [Ni(H2O)6]2+ Lewis acid Lewis base Hexa aquo nickel ion Pb2+ + 4 H2O [Pb(H2O)4]2+ Lewis acid Lewis base Tetra aquo lead ionDEMOL ewis acid - base Reaction ProductsLewis acid - base Reaction ProductsNet Reaction Examples Cu2+ + 4 H2O [Cu(H2O)4]2+ Lewis acid Lewis base Tetra aquo copper(II)ion H+ + H2O [H(H2O)]+ Lewis acid Lewis base Hydronium ionDEMOM etal Aquo Complex IonsMetal Aquo Complex IonsExample.

3 Cu2+(aq) + SO42- (aq) [Cu(H2O)4]2+ The metal ions in a salt solution bond to watermolecules to forms aquo complex solid:DEMO[Cu(H20)4]SO4tetra aquo copper(II) sufatePart 1. Acidity of CationsPart 1. Acidity of Cations EXPERIMENT VARIABLE Nitrate salts with different metal ions EXPERIMENT CONSTANT Water to dissolve salts is from same source and ofconstant pH (neutral or non-acidic).DEMO pH of Na+, Mg2+, and Al3+ Compare the pH of nitrate salts containing differentmetal Ion acid StrengthMetal Ion acid StrengthMetal Ion acid Strength: _____Al3+ > Mg2+ > Na+ Results suggest that metal ion acidity andmetal ion charge are linked Results suggest that metal ion acidity andmetal ion oxidizing agent strength are linked1 AVIIIA1H1s1 IIAIIIAIVAVAVIAVIIA2He1s23Li2s14Be2s25B2 s22p16C2s22p27N2s22p38O2s22p49F2s22p510N e2s22p611Na3s112Mg3s2 IIIB IVB VBVIBVIIBVIIIB VIIIB IB IIB13Al3s23p114Si3s23p215P3s23p316S3s23p 417Cl3s23p518Ar3s23p619K4s120Ca4s221Sc3d 14s222Ti3d24s223V3d34s224Cr3d54s125Mn3d5 4s226Fe3d64s227Co3d74s228Ni3d84s229Cu3d1 04s130Zn3d104s231Ga4s24p132Ge4s24p233As4 s24p334Se4s24p435Br4s24p536Kr4s24p637Rb5 s138Sr5s239Y4d15s240Zr4d25s241Nb4d35s242 Mo4d55s143Tc4d55s244Ru4d75s145Rh4d85s146 Pd

4 4d1047Ag4d105s148Cd4d105s249In5s25p150Sn 5s25p251Sb5s25p352Te5s25p453I5s25p554Xe5 s25p655Cs6s156Ba6s257La*5d16s272Hf5d26s2 73Ta5d36s274W5d46s275Re5d56s276Os5d66s27 7Ir5d76s278Pt5d96s179Au5d106s180Hg5d106s 281Tl6s26p182Pb6s26p283Bi6s26p384Po6s26p 485At6s26p586Rn6s26p687Fr7s188Ra7s289Ac# 6d17s2104 +6d27s2105 +6d37s2106 +6d47s2107 +6d57s2108 +6d67s2109 +6d77s2+ Element synthesized,but no official name assignedMetal Ion AcidityAcid strengthOxidizing agent strengthAcidity of Metal IonsAcidity of Metal IonsReminder:Metal ionsBONDto electronpairs onwatermolecules!Acidity of Metal Ion ModelAcidity of Metal Ion Model Metal ion acid strength is related to its ability toattract and bond to electrons (oxidizing agent strength) + HMx+ O + When a metal ion bonds to a water molecule, thewater molecule s polarity increases and the protons inthe water molecule become more electron deficient Electron deficient proton/s in the bonded watermolecule (of the metal aquo complex ion) aredonated(bond) to an external water moleculeAcidity of Metal Ion Model[X(H2O)6]2+ + H2O [X(H2O)5(OH)]+ + [H-H2O]+ When protons bond to water molecules, H3O+ions are formed producing a pH describing acidity of metal ions:Q.

5 Complete a balanced equation to show formationof hydronium ions:Q. Complete a balanced equation to show formationof hydronium ions:+ [H3O]+[Al(H2O)5(OH)]2+[Al(H2O)6]3+ + HOH4Q. Complete a balanced equation to show formationof hydronium ions:Q. Complete a balanced equation to show formationof hydronium ions:+ 2 [H3O]+[Al(H2O)4(OH)2]+[Al(H2O)6]3+ + 2 HOHPart 2. Complexation ReactionsPart 2. Complexation Reactions The reaction of a Lewis acid with a Lewis base (NH3, OH-, ..).Data Analysis What kinds of observations allow you to knowthat a complexation reaction is occurring? Are Lewis acid - base reaction results predictablefrom a) metal ion acid strength? b) the position ofthe metal ion s element in the Periodic Table?Part 2 Lewis acid - base ReactionsPart 2 Lewis acid - base ReactionsLewis acids Metal aquo complex ions Formula for metal aquo complex ion is providedLewis Bases OH- (NaOH) NH3 Part 2 Lewis acid - base ReactionsPart 2 Lewis acid - base ReactionsExample Al exists as [Al(H2O)6]3+ Add NaOHDEMO If reaction occurs with a charged Lewis basesuch as OH-, the product may be a solublecomplex ion or an uncharged insoluble Aquo Complex Ion Reactions Formation of a soluble complex ion:[Al (H2O)6]3+ + OH- [Al(H2O)5(OH)]2+ + H2 OMetal Aquo Complex Ion ReactionsFormation of an insoluble complex:[Al (H2O)6]3+ + 3OH- [Al(H2O)3(OH)3] + 3H2 OTraditional net precipitation equation: Al 3+(aq) + 3OH- (aq) Al(OH)3 (s) Precipitation reactions are Lewis acid - base reactions!

6 5 Metal Aquo Complex Ion ReactionsAddition of excess hydroxide ions to theprecipitated hydroxide complex results in theformation of a soluble complex ion:[Al (H2O)3(OH)3] + 3OH- [Al(OH)6]3- + 3 H2 OLewis acid - base Reactions 1:1 1:2 1:3 1:4 1:5 1: 6 Stoichiometry of Reaction Products: Al3+ to OH- Note that water molecules in the metal ionaquo complex are replaced with OH- ions[Al (H2O)6] + 6 OH- [Al(OH)6]3- + 6 H2O [Al(H2O)6]3+ [Al(H2O)5(OH)]2+ [Al(H2O)4(OH)2] + [Al(H2O)3(OH)3] [Al(H2O)2(OH)4]- [Al(H2O) (OH)5] 2- [Al(OH)6]3-Addition of base (NaOH) Lewis acid - base reactions are reversibleequilibrium systemsAddition of acid (H+) Lewis acids bond to the best availablebase. - an acid does not react (bond) to any base .+ base no reaction Wanna give me a try?

7 acid - base If a better base is available a Lewis acid willreact (exchange partners)! acid - base + better base ReactionLewis acid - base Replacement ReactionsLewis acid - base Replacement Reactions Complexes react if a better partner ( acid or base )is available so as to form a more stable is a complex of Fe that binds to/transports oxygen6Q. The acid exchanging base partners is H+. Which is the BEST base , Cl- or HOH?Q. The acid exchanging base partners is H+. Which is the BEST base , Cl- or HOH? acid base base acid HCl-H + O HCl- H H + O HH+ bonds to water (best base ) rather than Cl-. The bonded base - acid product = complex :Replacement of water molecules in [Cu (H2O)4]2+with ammonia Complex Ion Replacement Reactions[Cu (H2O)4]2++ 4 NH3 [Cu(NH3)4]2+ + 4 H2 ODEMOT etra aquo Cu(II) ionTetra ammine Cu(II) ionExample:Replacement of water molecules in [Cu (H2O)4]2+with ammonia Complex Ion Replacement Reactions[Cu (H2O)4]2++ 4 NH3 [Cu(NH3)4]2+ + 4 H2 ODEMOT etra aquo Cu(II) ionTetra ammine Cu(II) ionAquo Complex Ion Replacement ReactionsNet reaction:[Cu(H2O)4]2++ 4 NH3 [Cu(NH3)4]2+ + 4 H2O Tetra aquo Cu(II) nitrate[Cu(H2O)4 ](NO3)2 + 4 NH3 [Cu(NH3)4](NO3)2 + 4 H2 OTetra ammine Cu(II)nitrate The base NH3 bonded to Cu2+ in [Cu(NH3)4]2+ willexchange partners if a better Lewis acid than Cu(II)ions are Complex Ion Replacement Reactions[Cu(NH3)4]2+DEMO.

8 Addition of H+Aquo Complex Ion Replacement ReactionsAquo Complex Ion Replacement Reactions[Cu(H2O)4]2++ 4 NH3 [Cu(NH3)4]2+ + 4 H2O + H+ NH4+ Upon addition of H+, NH3 bonds to H+ (ratherthan Cu2+). Cu2+ re-bonds to If a precipitate forms upon addition of NH3(aq), themetal aquo complex ion is reacting with the SMALLAMOUNT of OH- ions present in NH3(aq): NH3(aq) + HOH(l) NH4+ (aq) + OH- (aq)Reactions with NH3 DEMOA ddition of NH3 to Cu2+resulting in a copperhydroxide ppt.[Cu(H2O)4]2+ + 2 OH- [Cu (H2O)2(OH)2] + 2 H2 OAquo Complex Ion ReactionsAquo Complex Ion Reactions[Cu(NH3)4]2+[Cu(H2O)4]2+ Colored transition metal complex ions altercolor upon bonding to a different Lewis IonsComplex Ions Complex ions are the chemical basis forcolorful paint Complex Ion ReactionsAquo Complex Ion Reactions[Cu(NH3)4]2+[Cu(H2O)4]2+ The charge on a aquo metal complex ionwill = the metal ion charge if the bondedLewis base is uncharged ( , H2O or NH3)Example:Replacement of neutral water molecules in [Cu(H2O)4]2+with a charged Lewis base - chloride Complex Ion Replacement ReactionsDEMO[Cu(Cl)4]2-[Cu(H2O)4]2+Q.

9 Complete the equation below:Aquo Complex Ion Replacement Reactions [Cu (H2O)4]2+ + 4 Cl- _____[Cu(Cl)4]2- + 4 H2O The charge on the complex ion alters due toreplacement of a neutral Lewis base (water) with acharged Lewis base8 Questions?Contact