Embed Size (px)
Citation preview
1
E5 Lewis Acids and Bases: lab 2March 26, 27,and 31
E5 Lewis Acids and Bases: lab 2March 26, 27,and 31
Session one labParts 1and 2A
Session two labSession two labParts 2B, 3, and 4Parts 2B, 3, and 4
Lewis Acid-Base ReactionsLewis Acid-Base Reactions
• Metal ions are Lewis acids and BOND to electronpairs on Lewis bases (e.g. water molecules)!
= [Na(H2O)6]+
Hexaaquosodium ion
Lewis Acid-Base ReactionsLewis Acid-Base Reactions
Net Reaction Examples
Ni2+ + 6 H2O [Ni(H2O)6]2+
Lewis acid Lewis base Hexaaquonickel ion
Na+ + 6 H2O [Na(H2O)6]+
Lewis acid Lewis base Hexaaquosodium ion
• Metal ions may react with - bond to - a differentLewis base than water
Lewis Acid-Base Reactions
[Ni (H2O)6]2++ 6 NH3 → [Ni(NH3)6]
2+ + 6 H2O
Hexaaquonickel(II) ion Hexaamminenickel(II) ion
Lewis Acid-Base ReactionsLewis Acid-Base Reactions
Nickel ions bonded to different Lewis bases
Colored aquo transition metal complex ionsalter color upon bonding to a new Lewis base.
Charge of the Complex Product
[Co(Cl)4]2-[Co(H2O)4]2+
The charge on the complex product = thealgebraic sum of the oxidation number of themetal and the charge/s of the bonded base/s.
2
Charge of the Complex ProductCharge of the Complex Product
[Ni(H2O)4(OH)2]Tetraaquodihydroxonickel
[Ni(H2O)6]2+
Hexaaquonickel ion
The complex will be insoluble if the complexproduct charge = zero
+ 2 OH- Nickelhydroxide
Nickelnitrate
Part 2B. Complexation, Structure and PeriodicityPart 2B. Complexation, Structure and Periodicity
• Compare the reactions of different metal aquocomplex ions (pre-transition, transition, and post-transition) with the Lewis bases NH3 and OH-
Lewis Acid-Base Reaction Extent
A Lewis acid must be able to bond with a Lewis
base if reaction is to occur
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.
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
≈ pH 6.7
≈ pH 3.4
“I’m Al3+ . I’m a strong post-transition Lewis acid!”
“ Na+,you areweak
Reaction extent is linked to Lewis acid strength
Pre-transition, transition, and post-transition metalions differ in Lewis acid strength
0.1 M solutions
3
Lewis Acid-Base Reaction ExtentLewis Acid-Base Reaction Extent
• The Lewis 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] + + OH- = no rxn
[Al(H2O)6]3+ + 6 OH- = rxn
Lewis Acid-Base Reaction Extent
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+ > Na+
Lewis Acid-Base Reaction Extent
Acid strength: Al3+ > Na+
Example 3 Na+ (aq) does not react with OH-: [Na (H2O)6]+ + OH- → no reaction
DEMO
Lewis Acid-Base Reaction Extent
Post-transition metal ions bond well to and
react extensively with OH- ions
Transition metal ions bond well to and react
extensively with NH3
Reaction Extent of Metal Ions
[Ni (H2O)6]2++ 6 NH3 → ___________________ [Ni(NH3)6]
2+ + 6 H2O
[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+
Reminder: Lewis Acid-Base reactions arereversible equilibrium systems
4
Lewis Acid-Base Reaction Extent
[Hg (H2O)4]2+ + 4 I - [Hg (I)4]
2- + 4 H2O
Lewis Acid-Base Reaction Extent
Reaction extent is concentration dependent.
[Hg(H2O)4]2+ + x I-
(aq) ↔ [Hg(I)x]?
(aq) + x H2O(aq)
DEMO:1. Add 0.10 M Hg2+ to 0.10 M I-.2. Add 0.10 M Hg2+ to 1.0 M I-.
1. Add 0.1 M Hg(NO3)2 to 0.1 M KI.
2. Add 0.1 M Hg(NO3)2 to 1.0 M KI.
Lewis Acid-Base Reaction Extent
[Hg(H2O)4]2+ + x I-
(aq) ↔ [Hg(I)x]?(aq)
+ x H2O(aq)
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
Q. What is the formula for Product 1? __________________[Hg(H2O)2(I)2]
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
5
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 ppt of silver chloride.[Ag(H2O)2]
+ + Cl- ↔ [Ag(H2O)(Cl)] + H2O
Addition of a BETTER base to a precipitate (e.g.,silver chloride) will cause a new acid-base reactionto occur between the metal ion and the BETTERbase and result in an equilibrium shift in theprecipitation reaction:
Information
• The transition ion Ag+ forms strong bonds with NH3
• Ag-NH3 bonds are more stable than Ag-H2O or
Ag-Cl bonds.
Precipitation ReactionsPrecipitation Reactions
1. Formation of silver chloride ppt.2. Addition of NH3
[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?
Answer?______________________ Silver chloride + NH3
[Ag(NH3)2]+
6
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
1. Addition of 0.1M NaCl to 0.1 M AgNO3.2. Addition of 5 M NH3 to step 1 products.3. Addition of acid (HNO3 ) to step 2 products.
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)]+
Q. Predict what you will OBSERVE if you reversethe addition of reagents:
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 1 products.
DEMO
1. Addition of 5 M NH3 to 0.1M AgNO32. Addition of 0.1 M NaCl to product of step 1.
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
