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E5 Lewis Acids and Bases: lab 2Nov. 12 - 18
E5 Lewis Acids and Bases: lab 2Nov. 12 - 18
Session one labParts 1and 2A
Session two labSession two labParts 2B, 3, and 4Parts 2B, 3, and 4
Lewis AcidsLewis Acids
Electron deficient species ; potential electronpair acceptors.
Lewis acids: H+ Cu2+ Al3+
“I’m deficient!”
Acid
Lewis BasesLewis Bases
Electron rich species; electron pair donors.
(ammine) (hydroxo) (aquo)
Ammonia hydroxide ion water__
Lewis Acid-Base ReactionsLewis Acid-Base Reactions
• Metal ions are Lewis acids and BONDto electron pairs on water molecules (Lewis bases)!
Lewis Acid-Base ReactionsLewis Acid-Base Reactions
Net 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 ion
• Aquo metal complex ions may react with - bondto a different Lewis base than water
Lewis Acid-Base Reactions
[Cu (H2O)4]2++ 4 NH3 → [Cu(NH3)4]
2+ + 4 H2O
Tetra aquo Cu(II) ion Tetra ammine Cu(II) ion
2
Lewis Acid-Base ReactionsLewis Acid-Base Reactions
[Cu(NH3)4]2+[Cu(H2O)4]
2+
Colored aquo transition metal complex ionsalter color upon bonding to a different Lewisbase.
Lewis Acid-Base ReactionsLewis Acid-Base Reactions
[Cu(NH3)4]2+[Cu(H2O)4]
2+
The charge on an aquo metal complex ionwill = the metal ion charge if the bondedLewis base is uncharged (e.g., H2O or NH3)
•The charge on a metal complex ion will alter ifthe neutral Lewis base (e.g. water) is replacedwith a charged Lewis base
Lewis Acid-Base Reactions
DEMO
[Cu(Cl)4]2-[Cu(H2O)4]2+
Q. Complete the equation below:
Aquo Complex Ion Replacement Reactions
[Cu (H2O)4]2+ + 4 Cl- → ___________________[Cu(Cl)4]
2- + 4 H2O
Part 2B. Complexation, Structure and PeriodicityPart 2B. Complexation, Structure and Periodicity
Discussion Q 4 & 5
• Compare the reactions of different metal aquocomplex ions with the Lewis bases NH3 and OH-
Compare the Lewis acid-base reactions of pre-transition, transition, and post-transition aquocomplex ions with Lewis bases.
Reaction Extent of Lewis Acids and BasesReaction Extent of Lewis Acids and Bases
Lewis acids and bases react to different extents;some never reach the “finish line”
Acid-Base 1 Acid-Base 2 race to the “finish line
3
Lewis Acid-Base Reaction Extent
A Lewis acid must form a strong bond with a
Lewis base for an extensive reaction to occur. 1A VIIIA1H1s1 IIA IIIA IVA VA VIA VIIA
2He1s2
3Li2s1
4Be2s2
5B
2s22p1
6C
2s22p2
7N
2s22p3
8O
2s22p4
9F
2s22p5
1 0Ne
2s22p6
1 1Na3s1
1 2Mg3s2 IIIB IVB VB VIB VIIB VIIIB ⇔ VIIIB IB IIB
1 3Al
3s23p1
1 4Si
3s23p2
1 5P
3s23p3
1 6S
3s23p4
1 7Cl
3s23p5
1 8Ar
3s23p6
1 9K4s1
2 0Ca4s2
2 1Sc
3d14s2
2 2Ti
3d24s2
2 3V
3d34s2
2 4Cr
3d54s1
2 5Mn
3d54s2
2 6Fe
3d64s2
2 7Co
3d74s2
2 8Ni
3d84s2
2 9Cu
3d1 04s1
3 0Zn
3d1 04s2
3 1Ga
4s24p1
3 2Ge
4s24p2
3 3As
4s24p3
3 4Se
4s24p4
3 5Br
4s24p5
3 6Kr
4s24p6
3 7Rb5s1
3 8Sr5s2
3 9Y
4d15s2
4 0Zr
4d25s2
4 1Nb
4d35s2
4 2Mo
4d55s1
4 3Tc
4d55s2
4 4Ru
4d75s1
4 5Rh
4d85s1
4 6Pd
4d10
4 7Ag
4d1 05s1
4 8Cd
4d1 05s2
4 9In
5s25p1
5 0Sn
5s25p2
5 1Sb
5s25p3
5 2Te
5s25p4
5 3I
5s25p5
5 4Xe
5s25p6
5 5Cs6s1
5 6Ba6s2
5 7La*
5d16s2
7 2Hf
5d26s2
7 3Ta
5d36s2
7 4W
5d46s2
7 5Re
5d56s2
7 6Os
5d66s2
7 7Ir
5d76s2
7 8Pt
5d96s1
7 9Au
5d1 06s1
8 0Hg
5d1 06s2
8 1Tl
6s26p1
8 2Pb
6s26p2
8 3Bi
6s26p3
8 4Po
6s26p4
8 5At
6s26p5
8 6Rn
6s26p6
8 7Fr7s1
8 8Ra7s2
8 9Ac#
6d17s2
1 0 4 +
6d27s2
1 0 5 +6d37s2
1 0 6 +6d47s2
1 0 7 +6d57s2
1 0 8 +6d67s2
1 0 9 +6d77s2
+ Element synthesized,but no official name assigned
• Pre-transition, transition, and post-transition metalions differ in ability to bond well with different bases(e.g. OH- and NH3) because of differences in metalion electron configurations.
≈ pH 6.7≈ pH 3.4
“I’m Al3+ . I’m a strong post-transitionLewis acid!”
“ Na+,you areweak
Reaction extent is dependent on Lewis acid strength Pre-transition, transition, and post-transition metalions differ in Lewis acid strength
0.1 M solutions1A VIIIA1H1s1 IIA IIIA IVA VA VIA VIIA
2He1s2
3Li2s1
4Be2s2
5B
2s22p1
6C
2s22p2
7N
2s22p3
8O
2s22p4
9F
2s22p5
1 0Ne
2s22p6
1 1Na3s1
1 2Mg3s2 IIIB IVB VB VIB VIIB VIIIB ⇔ VIIIB IB IIB
1 3Al
3s23p1
1 4Si
3s23p2
1 5P
3s23p3
1 6S
3s23p4
1 7Cl
3s23p5
1 8Ar
3s23p6
1 9K4s1
2 0Ca4s2
2 1Sc
3d14s2
2 2Ti
3d24s2
2 3V
3d34s2
2 4Cr
3d54s1
2 5Mn
3d54s2
2 6Fe
3d64s2
2 7Co
3d74s2
2 8Ni
3d84s2
2 9Cu
3d1 04s1
3 0Zn
3d1 04s2
3 1Ga
4s24p1
3 2Ge
4s24p2
3 3As
4s24p3
3 4Se
4s24p4
3 5Br
4s24p5
3 6Kr
4s24p6
3 7Rb5s1
3 8Sr5s2
3 9Y
4d15s2
4 0Zr
4d25s2
4 1Nb
4d35s2
4 2Mo
4d55s1
4 3Tc
4d55s2
4 4Ru
4d75s1
4 5Rh
4d85s1
4 6Pd
4d10
4 7Ag
4d1 05s1
4 8Cd
4d1 05s2
4 9In
5s25p1
5 0Sn
5s25p2
5 1Sb
5s25p3
5 2Te
5s25p4
5 3I
5s25p5
5 4Xe
5s25p6
5 5Cs6s1
5 6Ba6s2
5 7La*
5d16s2
7 2Hf
5d26s2
7 3Ta
5d36s2
7 4W
5d46s2
7 5Re
5d56s2
7 6Os
5d66s2
7 7Ir
5d76s2
7 8Pt
5d96s1
7 9Au
5d1 06s1
8 0Hg
5d1 06s2
8 1Tl
6s26p1
8 2Pb
6s26p2
8 3Bi
6s26p3
8 4Po
6s26p4
8 5At
6s26p5
8 6Rn
6s26p6
8 7Fr7s1
8 8Ra7s2
8 9Ac#
6d17s2
1 0 4 +
6d27s2
1 0 5 +6d37s2
1 0 6 +6d47s2
1 0 7 +6d57s2
1 0 8 +6d67s2
1 0 9 +6d77s2
+ Element synthesized,but no official name assigned
Metal Ion Lewis Acid Strength
Acid strength
Oxidizing agent strength
Lewis Acid-Base Reaction ExtentLewis Acid-Base Reaction Extent
• The acid strength of Al3+ is greater than Na+
• Al3+ bonds well to hydroxide ions and reacts moreextensively with hydroxide ions than Na+
[Na(H2O)6]2+
(aq)+ OH- (aq) versus [Al(H2O)6]
3+(aq) + OH-
(aq)
Extent of Reaction of Aquo Complex Ions
Example 1 Al3+ (aq) reacts extensively with OH-: [Al (H2O)6]3+ + 6 OH- → [Al(OH)6]3- + 6 H2O
1:1 1:2 1:3 1:4 1:5 1: 6Stoichiometry of Reaction Products: Al3+ to OH-
DEMO
Acid strength: Al3+ > Hg2+ > Na+
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Extent of Reaction of Aquo Complex Ions
Acid strength: Al3+ > Hg2+ > Na+
Example 2 Hg2+ (aq) reacts with 2 OH-: [Hg (H2O)4]2+ + 2 OH-→ [Hg (H2O)2(OH)2] + 2H2O
1:1 1: 2Stoichiometry of Reaction Products: Hg2+ to OH-
DEMO
Extent of Reaction of Aquo Complex Ions
Acid strength: Al3+ > Hg2+ > Na+
Example 3 Na+ (aq) does not react with OH-: [Na (H2O)6]+ + OH- → no reaction
DEMO
Reaction Extent of Aquo Complex Ions
Post-transition metal ions bond well to and
react extensively with OH- ions
Transition metal ions bond well to and react
extensively with NH3
Lewis Acid-Base Reaction Extent
Example:
Hg (II) reacts with 2 OH- :[Hg (H2O)4]
2+ + 2 OH- [Hg (H2O)2(OH)2] + 2 H2O
Hg (II) reacts with 4 I - : [Hg (H2O)4]
2+ + 4 I - [Hg (I)4]2- + 4 H2O
A Lewis acid may react to different extents withdifferent Lewis bases
[Hg(H2O)4]2+(aq)
↓↑ [Hg(H2O)3(I)]+
(aq)
↓↑ [Hg(H2O)2(I)2](s)
↓↑ [Hg(H2O)(I)3] -(aq)
↓↑ [Hg(I)4]2-
(aq)
Ad
dit
ion
of
I-
Ad
dit
ion
of
Hg
2+
DEMO
Reminder: Lewis Acid-Base reactions arereversible equilibrium systems
Lewis Acid-Base Reaction Extent
Extent of reaction is concentration dependent.
[Hg(H2O)4]2+ + 4I-
(aq) ↔ [Hg(I)4]2-
(aq) + 4 H2O(aq)
DEMO:1. Add 0.1 M Hg2+ to 0.1 M I-.2. Add 0.1 M Hg2+ to 1.0 M I-.
Products: : 1 2
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Part 3. Solubility and ComplexationPart 3. Solubility and Complexation
• Collect data on the behavior ofdifferent metal ion precipitateswhen NH3 or OH- is added.Does the precipitate dissolvewhen NH3 and OH- is added?
- Periodic trends?
Precipitation ReactionsPrecipitation Reactions
DEMO 1:[Ag(H2O)2]
+ + Cl- ↔ silver chloride precipitate
Precipitation reactions are Lewis acid-base reactions Precipitation reactions are equilibrium systems
Q. When 0.1 M NaCl is added to 0.1 M AgNO3, aprecipitate of silver chloride forms. Choose the correctequation for the net Lewis precipitation reaction.
Q. When 0.1 M NaCl is added to 0.1 M AgNO3, aprecipitate of silver chloride forms. Choose the correctequation for the net Lewis precipitation reaction.
Information: Ag + exists as [Ag(H2O)2]+
1. [Ag(H2O)2]+ + Cl- ↔ [Ag(H2O)(Cl)] + H2O2. [Ag(H2O)2]+ + 2 Cl- ↔ [AgCl2]- + 2 H2O3. [Ag(H2O)2]+ + 2 Cl- ↔ [Ag(OH)(Cl)] + HCl
note: The traditional net ppt. equation is: Ag+ (aq) + Cl- (aq) → Ag(Cl)(s)
Lewis Acid-Base Precipitation ReactionsLewis Acid-Base Precipitation Reactions
Example: Add NH3 to a Ag ppt.[Ag(H2O)2]
+ + Cl- ↔ [Ag(H2O)(Cl)] + H2O
Addition of a BETTER base to a precipitate willcause a new acid-base reaction to occur and resultin an equilibrium shift in the precipitation reaction:
[Ag(H2O)2]+ + Cl- ↔ [Ag(H2O)(Cl)] + H2O
Add NH3 to precipitated silver chloride:
Information• The transition ion Ag+ forms strong bonds with NH3• Ag-NH3 bonds are more stable than Ag-H2O or Ag-Cl bonds.
DEMO
Precipitation ReactionsPrecipitation Reactions
Observations: Upon addition of NH3, the silver chloride ppt.dissolves and a clear, colorless solution forms.
ppt of [Ag(H2O)(Cl)] + NH3
[Ag(H2O)(Cl)]
[Ag(NH3)2]+
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Reminder: A Lewis acid will react (exchangepartners) if a better base becomes available!
Acid1-Base1 + Base2 → reaction[Ag - (H2O)2]+ + 2 NH3 = [Ag - (NH3)2]+ + 2 H2O
[Ag(H2O)2]+
(aq) + Cl-(aq) ↔ [Ag (H2O)(Cl)](s)+H2O(l)[Ag(H2O)2]+
(aq) + Cl-(aq) ↔ [Ag (H2O)(Cl)](s)+H2O(l)
Add the “ better” base NH3.
Dissolving of AgCl(s)
+2 NH3(aq)
[Ag(NH3)2]+
+ 2 H2O
[Ag(H2O)2]+
Reaction takes place. The Ag+
forms a soluble ammine complexion with the NH3, the silverchloride ppt. dissolves and aclear, colorless solution remains
Precipitation ReactionsPrecipitation Reactions
Q. What will you observe if you add acid (5 M H+) tothe product mixture formed upon adding ammoniato precipitated silver chloride?
Add H+
Silver chloride + NH3
[Ag(NH3)2]+
Reminder: Hydrogen ion is the BEST Lewis acid!If a better Lewis acid is available a Lewis base willreact (exchange partners)!
Acid1-Base1 + → reactionH+
Precipitation ReactionsPrecipitation Reactions
DEMO 3 : Add H+ (HNO3)
Silver chloride + NH3
[Ag(NH3)2]+
Upon addition of acid the silver chloride ppt. reforms.
If a better acid is available a Lewis basewill react (exchange partners)!
Acid1-Base1 + Acid2 → Acid2-Base1
[Ag - (NH3)2]+ + 2 H+
= 2 [H - (NH3)]+
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Q. Predict what you will OBSERVE if you:
1. Add 5 M NH3 to 10 mL of 0.1 M AgNO3.
___________?
2. Add 10 mL of 0.1 M NaCl to the step 1products.
+ NaCl (aq) = ____________?
DEMO
Observations
1. Add 5 M NH3 to 10 mL of 0.1 M AgNO3.
= clear and colorless solution Ag+ bonds to NH3 = [Ag(NH3)2]+
2. Add 10 mL of 0.1 M NaCl to the step 1 products.
+ NaCl (aq) = clear and colorless solution
Ag+ forms a stronger bond with NH3 than Cl -
Ag+ remains bonded to NH3
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