E5 Lewis Acids and Bases: lab 2 Session one lab Parts 1and 2A Part 2B. Complexation, Structure and Periodicity Compare the reactivity of aquo complex ions containing pre-transition, transition, and post-transition metal ions. Discussion Q 4 & 5 Compare the complexation of metal ions with NH 3 and OH - Session two lab Parts 2B, 3, and 4 Aquo Complex Ions Metal ions exist as aquo complex ions in aqueous solution Colored aquo complex ions contain transition metal ions with unfilled d orbitals. Examples Aquo Complex Ion Reactions Aquo metal complex ions may react with and bond to a different Lewis base. [H(H 2 O)] + Hydronium ion [Cu(H 2 O) 4 ] 2+ Tetra aquo copper(ii)ion [Cu(H 2 O) 4 ] 2+ + 4 NH 3 [Cu(NH 3 ) 4 ] 2+ + H 2 O [Pb(H 2 O) 4 ] 2+ Tetra aquo lead ion [Ni(H 2 O) 6 ] 2+ Hexa aquo nickel ion 1
Reaction Extent of Lewis Acids and Bases Reaction extent refers to the point of equilibrium and is indicated by the value of the equilibrium constant K f. Extent of Reaction of Aquo Complex Ions Reactivity of metal aquo complex ions are linked to acid strength. 0.1 M solutions Acid-Base 1 Acid-Base 2 race to the finish line Lewis acids and bases react to different extents; some never reach the finish line ph 3.4 I m Al 3+. I m a strong posttransition Lewis acid! ph 6.7 Na +, you are weak 1A 1 H 1s1 IIA IIIA IVA VA VIA VIIA 3 Li 2s 1 1 1 Na 3s 1 1 9 K 4s 1 3 7 Rb 5s 1 5 5 Cs 6s 1 8 7 Fr 7s 1 4 Be 2s 2 1 2 Mg 3s2 IIIB IVB VB VIB VIIB VIIIB! VIIIB IB IIB 2 0 Ca 4s 2 3 8 Sr 5s 2 Aquo Complex Ion Reactions Acid strength 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 Sc Ti V Cr Mn Fe Co Ni 3d 1 4s 2 3d 2 4s 2 3d 3 4s 2 3d 5 4s 1 3d 5 4s 2 3d 6 4s 2 3d 7 4s 2 3d 8 4s 2 3 9 4 0 4 1 4 2 4 3 4 4 4 5 4 6 Y Zr Nb Mo Tc Ru Rh Pd 4d 1 5s 2 4d 2 5s 2 4d 3 5s 2 4d 5 5s 1 4d 5 5s 2 4d 7 5s 1 4d 8 5s 1 4d 10 VIIIA 2 He 1s 2 5 6 7 8 9 1 0 B C N O F Ne 2s 2 2p 1 2s 2 2p 2 2s 2 2p 3 2s 2 2p 4 2s 2 2p 5 2s 2 2p 6 1 3 1 4 1 5 1 6 1 7 1 8 Al Si P S Cl Ar 3s 2 3p 1 3s 2 3p 2 3s 2 3p 3 3s 2 3p 4 3s 2 3p 5 3s 2 3p 6 2 9 3 0 3 1 3 2 3 3 3 4 3 5 3 6 Cu Zn Ga Ge As Se Br Kr 3d 1 0 4s 1 3d 1 0 4s 2 4s 2 4p 1 4s 2 4p 2 4s 2 4p 3 4s 2 4p 4 4s 2 4p 5 4s 2 4p 6 4 7 4 8 4 9 5 0 5 1 5 2 5 3 5 4 Ag Cd In Sn Sb Te I Xe 4d 1 0 5s 1 4d 1 0 5s 2 5s 2 5p 1 5s 2 5p 2 5s 2 5p 3 5s 2 5p 4 5s 2 5p 5 5s 2 5p 6 5 6 Ba 5 7 7 2 La* Hf 7 3 Ta 7 4 W 7 5 Re 7 6 Os 7 7 Ir 7 8 Pt 7 9 Au 8 0 Hg 8 1 Tl 8 2 Pb 8 3 Bi 8 4 Po 8 5 At 8 6 Rn 6s 2 5d 1 6s 2 5d 6s 5d 6s 5d 6s 5d 6s 5d 6s 2 5d 6s 2 5d 6s 6s 6p 6s 2 6p 2 6s 2 6p 3 6s 2 6p 4 6s 2 6p 5 6s 2 6p 6 2 2 3 2 7 9 1 5d 1 0 6s 1 5d 1 0 6s 2 8 8 8 9 1 0 4 1 0 5 1 0 6 1 0 7 1 0 8 1 0 9 + Element synthesized, Ra Ac # + + + + + + but no official name assigned 7s 2 6d 1 7s 2 6d 2 7s 2 6d 3 7s 2 6d 4 7s 2 6d 5 7s 2 6d 6 7s 2 6d 7 7s 2 Extent of Reaction of Aquo Complex Ions Acid strength: Al 3+ > Hg 2+ > Na + Example 1 Al 3+ (aq) reacts extensively with OH - : [Al (H 2 O) 6 ] 3+ + 6 OH - [Al(OH) 6 ] 3- + 6 H 2 O 1:1 1:2 1:3 1:4 1:5 1: 6 Stoichiometry of Reaction Products: Al 3+ to OH - 2
Extent of Reaction of Aquo Complex Ions Acid strength: Al 3+ > Hg 2+ > Na + Example 2 Hg 2+ (aq) reacts with 2 OH - : [Hg (H 2 O) 4 ] 2+ + 2 OH - [Hg (H 2 O) 2 (OH) 2 ] + 2H 2 O Extent of Reaction of Aquo Complex Ions Acid strength: Al 3+ > Hg 2+ > Na + Example 3 Na + (aq) does not react with OH - : [Na (H 2 O) 6 ] + + OH - no reaction 1:1 1: 2 Stoichiometry of Reaction Products: Hg 2+ to OH - Reaction Extent of Aquo Complex Ions The extent of reaction is linked to the acid strength of the metal ion in the aquo complex ion. Reactions of Aquo Complex Ions A strong Lewis acid (aquo complex ion) will not react or react extensively with all Lewis bases. A Lewis acid must form a strong bond with a Lewis base for an extensive reaction to occur. [Na(H 2 O) 6 ] + (aq) + OH- (aq) versus [Al(H 2 O) 6 ]3+ (aq) + OH- (aq) The acid strength of Al 3+ is greater than the acid strength of Na + The K f for the formation of hydroxides of Al 3+ is greater than the K f for the formation of hydroxides of Na + 3
1A 1 H 1s1 IIA IIIA IVA VA VIA VIIA 3 Li 2s 1 1 1 Na 3s 1 1 9 K 4s 1 3 7 Rb 5s 1 5 5 Cs 6s 1 8 7 Fr 7s 1 4 Be 2s 2 1 2 Mg 3s2 IIIB IVB VB VIB VIIB VIIIB! VIIIB IB IIB 2 0 Ca 4s 2 3 8 Sr 5s 2 Aquo Complex Ion Reactions Pre-transition, transition, and post-transition metal ions differ in ability to bond well with bases (e.g. OH - and NH 3 ) because of differences in metal ion electron configurations. 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 Sc Ti V Cr Mn Fe Co Ni 3d 1 4s 2 3d 2 4s 2 3d 3 4s 2 3d 5 4s 1 3d 5 4s 2 3d 6 4s 2 3d 7 4s 2 3d 8 4s 2 3 9 4 0 4 1 4 2 4 3 4 4 4 5 4 6 Y Zr Nb Mo Tc Ru Rh Pd 4d 1 5s 2 4d 2 5s 2 4d 3 5s 2 4d 5 5s 1 4d 5 5s 2 4d 7 5s 1 4d 8 5s 1 4d 10 VIIIA 2 He 1s 2 5 6 7 8 9 1 0 B C N O F Ne 2s 2 2p 1 2s 2 2p 2 2s 2 2p 3 2s 2 2p 4 2s 2 2p 5 2s 2 2p 6 1 3 1 4 1 5 1 6 1 7 1 8 Al Si P S Cl Ar 3s 2 3p 1 3s 2 3p 2 3s 2 3p 3 3s 2 3p 4 3s 2 3p 5 3s 2 3p 6 2 9 3 0 3 1 3 2 3 3 3 4 3 5 3 6 Cu Zn Ga Ge As Se Br Kr 3d 1 0 4s 1 3d 1 0 4s 2 4s 2 4p 1 4s 2 4p 2 4s 2 4p 3 4s 2 4p 4 4s 2 4p 5 4s 2 4p 6 4 7 4 8 4 9 5 0 5 1 5 2 5 3 5 4 Ag Cd In Sn Sb Te I Xe 4d 1 0 5s 1 4d 1 0 5s 2 5s 2 5p 1 5s 2 5p 2 5s 2 5p 3 5s 2 5p 4 5s 2 5p 5 5s 2 5p 6 5 6 Ba 5 7 7 2 La* Hf 7 3 Ta 7 4 W 7 5 Re 7 6 Os 7 7 Ir 7 8 Pt 7 9 Au 8 0 Hg 8 1 Tl 8 2 Pb 8 3 Bi 8 4 Po 8 5 At 8 6 Rn 6s 2 5d 1 6s 2 5d 6s 2 5d 6s 2 5d 6s 2 5d 6s 2 5d 6s 2 5d 6s 2 5d 6s 6s 6p 6s 2 6p 2 6s 2 6p 3 6s 2 6p 4 6s 2 6p 5 6s 2 6p 6 2 3 4 5 6 7 9 1 5d 1 0 6s 1 5d 1 0 6s 2 8 8 8 9 1 0 4 1 0 5 1 0 6 1 0 7 1 0 8 1 0 9 + Element synthesized, Ra Ac # + + + + + + but no official name assigned 7s 2 6d 1 7s 2 6d 2 7s 2 6d 3 7s 2 6d 4 7s 2 6d 5 7s 2 6d 6 7s 2 6d 7 7s 2 Reactions of Aquo Complex Ions Transition metal ions bond well to NH 3 Post-transition metal ions bond well to OH - The Lewis acid and base must fit together like two pieces in a puzzle. Extent of Reaction of Aquo Complex Ions [Hg(H 2 O) 4 ] 2+ (aq) + 4 I- (aq) [Hg(I) 4 ]2- (aq) + 4 H 2 O (l) An aquo complex metal ion (Lewis acid) may react to different extents with different Lewis bases Example: Hg (II) reacts with 2 OH - : [Hg (H 2 O) 4 ] 2+ + 2 OH - [Hg (H 2 O) 2 (OH) 2 ] + 2 H 2 O Hg (II) reacts with 4 I - : [Hg (H 2 O) 4 ] 2+ + 4 I - [Hg (I) 4 ] 2- + 4 H 2 O Addition of I - [Hg(H 2 O) 4 ] 2+ (aq) [Hg(H 2 O) 3 (I)] + (aq) [Hg(H 2 O) 2 (I) 2 ] (s) [Hg(H 2 O)(I) 3 ] - (aq) [Hg(I) 4 ] 2- (aq) Addition of Hg 2+ 4
Reaction Extent of Aquo Complex Ions Even if K f is positive, the extent of reaction is concentration dependent. [Hg(H 2 O) 4 ] 2+ (aq) + 4I - (aq) [Hg(I) 4 ] 2- (aq) + 4 H 2 O (aq : 1. Add 0.1 M Hg 2+ to 0.1 M I -. 2. Add 0.1 M Hg 2+ to 1.0 M I -. [Hg(H 2 O) 4 ] 2+ (aq) + 4 I - (aq) [Hg(I) 4 ] 2- (aq) + 4 H 2 O (l) Observation 0.10 M Hg(NO 3 ) 2 + 0.10 M KI = mercury iodide(s). Q. What is the precipitate s formula? [Hg(H 2 O) 2 (I) 2 ] Products: : 1 2 Part 3. Solubility and Complexation Collect data on the behavior of different metal ion precipitates when NH 3 or OH - is added. Does the precipitate dissolve when NH 3 and OH - is added? Precipitation reactions are Lewis acid-base reactions Precipitation reactions are equilibrium systems 1: [Ag(H 2 O) 2 ] + + Cl - silver chloride precipitate - Periodic trends? 5
Q. When 0.1 M NaCl is added to 0.1 M AgNO 3, a precipitate of silver chloride forms. Choose the correct equation for the net Lewis precipitation reaction. Information: Ag + exists as [Ag(H 2 O) 2 ] + 1. [Ag(H 2 O) 2 ] + + Cl - [Ag(H 2 O)(Cl)] + H 2 O 2. [Ag(H 2 O) 2 ] + + 2 Cl - [AgCl 2 ] - + 2 H 2 O 3. [Ag(H 2 O) 2 ] + + 2 Cl - [Ag(OH)(Cl)] + HCl note: The traditional net equation is: Ag + (aq) + Cl - (aq) Ag(Cl) (s) Addition of a BETTER base to a precipitate will cause a new acid-base reaction to occur and result in an equilibrium shift in the precipitation reaction. Example - Add NH 3 to precipitated silver chloride: [Ag(H 2 O) 2 ] + + Cl - [Ag(H 2 O)(Cl)] + H 2 O Information - The transition ion Ag + forms strong bonds with NH 3 - Ag-NH 3 bonds are more stable than Ag-H 2 O or Ag-Cl bonds. A Lewis acid will react (exchange partners) if a better base becomes available! 2 : Add NH 3(aq) to precipitated silver chloride [Ag(H 2 O) 2 ] + + Cl - [Ag(H 2 O)(Cl)] + H 2 O [Ag(H 2 O)(Cl)] ppt. of [Ag(H 2 O)(Cl)] + NH 3 Acid1-Base1 + Base2 reaction [Ag - (H 2 O) 2 ] + + 2 NH 3 = [Ag - (NH 3 ) 2 ] + + 2 H 2 O 6
Dissolving of AgCl(s) [Ag(H (aq) + Cl- (aq) [Ag (H 2 O)(Cl)] (s) + H 2 O 2 O) 2 ] + (l) + 2 NH 3(aq) Observations: Upon addition of NH 3 (aq), the precipitate of silver chloride dissolved and a clear, colorless solution formed. Add the better base NH 3. [Ag(NH 3 ) 2 ] + + 2 H 2 O Reaction takes place. The Ag + forms a soluble ammine complex ion with the NH 3, the silver chloride ppt. dissolves and a clear, colorless solution remains [Ag(H 2 O)(Cl)] ppt of [Ag(H 2 O)(Cl)] + NH 3 [Ag(NH 3 ) 2 ] + NH 3 If a better Lewis acid is available a Lewis base will react (exchange partners)! - Hydrogen ion is the BEST Lewis acid! Q. What will you observe if you now add acid (5 M HNO 3 ) to the product mixture formed upon reaction of ammonia and silver chloride? What will happen to Ag + (aq)? Add HNO 3 [Ag(NH 3 ) 2 ] + NH 3 Acid1-Base1 + H + reaction Silver chloride + NH 3 7
If a better acid is available a Lewis base will react (exchange partners)! 3 : Add HNO 3 [Ag(NH 3 ) 2 ] + Silver chloride + NH 3 Upon addition of acid the silver chloride ppt. reforms. Acid1-Base1 + Acid2 Αcid2-Base1 [Ag - (NH 3 ) 2 ] + + 2 H + = 2 [H - (NH 3 )] + Q. Predict what you will OBSERVE if you: 1. Add 5 M NH 3 to 10 ml of 0.1 M AgNO 3. Observations 1. Add 5 M NH 3 to 10 ml of 0.1 M AgNO 3.? = clear and colorless solution 2. Add 10 ml of 0.1 M NaCl to the step 1 products. 2. Add 10 ml of 0.1 M NaCl to the step 1 products. + NaCl (aq) =? + NaCl (aq) = clear and colorless solution 8
Observations 1. Add 5 M NH 3 to 10 ml of 0.1 M AgNO 3. = clear and colorless solution Ag + bonds to NH 3 = [Ag(NH 3 ) 2 ] + 2. Add 10 ml of 0.1 M NaCl to the step 1 products. Q. Will a precipitate of lead iodide dissolve upon adding the base NH 3? Information Pb 2+ is a post-transition metal ion Post-transition metal ions do not bond well to NH 3. + NaCl (aq) = clear and colorless solution Ag + remains bonded to NH 3 Ag + forms a stronger bond with NH 3 than Cl - Lead iodide (s) + NH 3 (aq) =? Q. Will a precipitate of lead iodide dissolve upon adding the base NH 3? Observations Lead iodide (s) + NH 3 (aq) = ppt. does not dissolve Analysis Lead ions form more stable bonds with I - than with NH 3 or H 2 O. Questions? Contact nkerner@umich.edu 9