pre-transition, transition, and post-transition metal ions ...chem125/w08/6.lewisw08lab2key.pdf ·...

1

E5 Lewis Acids and Bases: lab 2

Session one labParts 1and 2A

Session two labSession two labParts 2B, 3, and 4Parts 2B, 3, and 4

Part 2B. Complexation, Structure and Periodicity

Discussion Q 4 & 5• Compare the complexation of metal ions with NH3 and OH-

Compare the reactivity of aquo complex ions containingpre-transition, transition, and post-transition metal ions.

Aquo Complex Ions

Examples

[Pb(H2O)4]2+

Tetra aquo lead ion[Ni(H2O)6]2+

Hexa aquo nickel ion

[Cu(H2O)4]2+

Tetra aquo copper(II)ion[H(H2O)]+

Hydronium ion

Metal ions exist as aquo complex ions in aqueous solution Colored aquo complex ions contain transition metal ionswith unfilled d orbitals.

Aquo Complex Ion Reactions

+ 4 NH3 → [Cu(NH3)4]2+ + H2O[Cu(H2O)4]2+

Aquo metal complex ions may react with andbond to a different Lewis base.

2

Reaction Extent of Lewis Acids and Bases

Reaction extent refers to the point of equilibrium and isindicated by the value of the equilibrium constant Kf.

Lewis acids and bases react to different extents; some neverreach the “finish line”

Acid-Base 1 Acid-Base 2 race to the “finish line

≈ pH 6.7

Extent of Reaction of Aquo Complex Ions

≈ pH 3.4

“I’m Al3+ . I’ma strong post-transitionLewis acid!”

“ Na+,you areweak

Reactivity of metal aquo complex ions are linked toacid strength.

0.1 M solutions

1A VIIIA

1H

1s1 IIA IIIA IVA VA VIA VIIA

2He1s2

3Li

2s1

4Be

2s2

5B

2s22p1

6C

2s22p2

7N

2s22p3

8O

2s22p4

9F

2s22p5

1 0Ne

2s22p6

1 1Na

3s1

1 2Mg

3s2 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 9K

4s1

2 0Ca

4s2

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 7Rb

5s1

3 8Sr

5s2

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 5Cs

6s1

5 6Ba

6s2

5 7

La*

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 7Fr

7s1

8 8Ra

7s2

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


Acid strength


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

DEMOAcid strength: Al3+ > Hg2+ > Na+

3


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


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

• The acid strength of Al3+ is greater than the acid strength of Na+

• The Kf for the formation of hydroxides of Al3+ is greater than theKf for the formation of hydroxides of Na+

[Na(H2O)6]+ (aq) + OH-

(aq) versus [Al(H2O)6]3+ (aq) + OH-

(aq)

The extent of reaction is linked to the acid strength ofthe metal ion in the aquo complex ion.

Reactions of Aquo Complex Ions

A strong Lewis acid (aquo complex ion) will notreact 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.

4

1A VIIIA

1H

1s1 IIA IIIA IVA VA VIA VIIA

2He1s2

3Li

2s1

4Be

2s2

5B

2s22p1

6C

2s22p2

7N

2s22p3

8O

2s22p4

9F

2s22p5

1 0Ne

2s22p6

1 1Na

3s1

1 2Mg

3s2 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 9K

4s1

2 0Ca

4s2

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 7Rb

5s1

3 8Sr

5s2

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 5Cs

6s1

5 6Ba

6s2

5 7

La*

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 7Fr

7s1

8 8Ra

7s2

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 metal ions differ inability to bond well with bases (e.g. OH- and NH3) because ofdifferences in metal ion electron configurations.

Reactions of Aquo Complex Ions

Transition metal ions bond well to NH3 Post-transition metal ions bond well to OH-

• The Lewis acid and base must “fit” together like two pieces in a puzzle.


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

An aquo complex metal ion (Lewis acid) may reactto different extents with different 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)

Add

ition

of

I-

Add

ition

of

Hg2+

[Hg(H2O)4]2+(aq) + 4 I-

(aq) ↔ [Hg(I)4]2-(aq)

+ 4 H2O(l)

DEMO

5

Reaction Extent of Aquo Complex Ions

Even if Kf is positive, the extent of reaction isconcentration dependent.

[Hg(H2O)4]2+(aq) + 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-.

DEMO Products: : 1 2

[Hg(H2O)4]2+ (aq) + 4 I-

(aq) ↔ [Hg(I)4]2- (aq)

+ 4 H2O(l)

Observation0.10 M Hg(NO3)2 + 0.10 M KI = mercury iodide(s).

Q. What is the precipitate’s formula?

___ ________[Hg(H2O)2(I)2]

Part 3. Solubility and Complexation

• Collect data on the behavior ofdifferent metal ion precipitateswhen NH3 or OH- is added.Does the precipitate dissolve whenNH3 and OH- is added?

- Periodic trends?

Precipitation Reactions

DEMO 1:[Ag(H2O)2]+ + Cl- ↔ silver chloride precipitate

Precipitation reactions are Lewis acid-base reactions Precipitation reactions are equilibrium systems

6

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 equation is: Ag+

(aq) + Cl- (aq) → Ag(Cl)(s)


[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 result inan equilibrium shift in the precipitation reaction.Example - 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.


[Ag(H2O)2]+ + Cl- ↔ [Ag(H2O)(Cl)] + H2O

DEMO 2 : Add NH3(aq) to precipitated silver chloride

ppt. of [Ag(H2O)(Cl)] + NH3

[Ag(H2O)2]+ Cl -

[Ag(H2O)(Cl)]

A Lewis acid will react (exchange partners) ifa better base becomes available!

Acid1-Base1 + Base2 → reaction[Ag - (H2O)2]+ + 2 NH3 = [Ag - (NH3)2]+ + 2 H2O

7

[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


Observations: Upon addition of NH3 (aq), the precipitate of silver chloridedissolved and a clear, colorless solution formed.

ppt of [Ag(H2O)(Cl)] + NH3

[Ag(H2O)2]+ Cl -

[Ag(H2O)(Cl)][Ag(H2O)2]+ Cl -

[Ag(NH3)2]+ NH3

If a better Lewis acid is available a Lewis base willreact (exchange partners)! - Hydrogen ion is the BEST Lewis acid!

Acid1-Base1 + → reactionH+


Q. What will you observe if you now add acid (5 M HNO3)to the product mixture formed upon reaction of ammoniaand silver chloride? What will happen to Ag+ (aq)?

Add HNO3

Silver chloride + NH3

[Ag(H2O)2]+ Cl -

[Ag(NH3)2]+ NH3

8


DEMO 3 : Add HNO3

Silver chloride + NH3

[Ag(H2O)2]+ Cl -

[Ag(NH3)2]+

Upon addition of acid the silver chloride ppt. reforms.

If a better acid is available a Lewis base willreact (exchange partners)!

Acid1-Base1 + Acid2 → Αcid2-Base1[Ag - (NH3)2]+ + 2 H+

= 2 [H - (NH3)]+

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 1 products.

+ NaCl (aq) = ____________?

DEMO

Observations


= clear and colorless solution


+ NaCl (aq) = clear and colorless solution

9

Observations


= clear and colorless solution Ag+ bonds to NH3 = [Ag(NH3)2]+


+ NaCl (aq) = clear and colorless solution

Ag+ forms a stronger bond with NH3 than Cl -Ag+ remains bonded to NH3

Q. Will a precipitate of lead iodide dissolve uponadding the base NH3?

Information• Pb 2+ is a post-transition metal ion• Post-transition metal ions do not bond well to NH3.

DEMO

Lead iodide (s) + NH3(aq) = ______________?

Q. Will a precipitate of lead iodide dissolve upon addingthe base NH3?

Observations

Lead iodide (s) + NH3(aq) = ppt. does not dissolve

Analysis• Lead ions form more stable bonds with I- than with NH3 or H2O.

Questions?Contact [email protected]

pre-transition, transition, and post-transition metal ions ...chem125/w08/6.lewisw08lab2key.pdf ·...

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