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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

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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

Questions?Contact nkerner@umich.edu