Lecture #27 Coordination Chemistry: Hydroxides & oxides (Stumm - - PowerPoint PPT Presentation

Lecture #27 Coordination Chemistry: Hydroxides & oxides

(Stumm & Morgan, Chapt.6: pg.272-275)

Benjamin; Chapter 8.1-8.6

David Reckhow CEE 680 #27 1

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Elemental abundance in crust

 O  Si  Al  Fe  Ca  Na  Mg  K  Ti  H  P  Mn  F

David Reckhow CEE 680 #2 2

Zinc

 An essential metal

 Needed for certain enzyme, e.g., alcohol dehydrogenase  Associate with a number of diseases

 Only one oxidation state (+2)

 Electrons: 3d10, 4s2 (like Mg: 3s2)

 Uses in plumbing

 Galvanized steel/iron – coat of Zn protects from oxidation

 Now mostly for mains and connections, not premise

 Copper Alloys

 Brass (Cu, Zn & <2% Pb),  Bronze (Cu, ~12% Sn, & others)

David Reckhow CEE 680 #27 3

Hydrolysis

 Metal accepts an electron from water and releases or

repels a proton

 Example: Zinc

 First step

 Zn(H2O)6 +2 = Zn(H2O)5OH+ + H+

 Second step

 Zn(H2O)5OH+ = Zn(H2O)4(OH)2 0 + H+

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[ ][ ]

] [ ) (

2 1 * + + +

= Zn H OH Zn K

[ ]

] [ ] [ ) (

2 2 * + +

= ZnOH H OH Zn K

Hydrolysis (cont.)

 Zinc example expressed as hydroxide formation

 First step

 Zn(H2O)6 +2 + OH- = Zn(H2O)5OH+ + H2O

 Second step

 Zn(H2O)5OH+ + OH- = Zn(H2O)4(OH)2 0+ H2O

David Reckhow CEE 680 #27 5

[ ]

] ][ [ ) (

2 1 − + +

= OH Zn OH Zn K

[ ]

] ][ [ ) (

2 2 − +

= OH ZnOH OH Zn K

Hydrolysis (cont.)

 Converting between the two forms

David Reckhow CEE 680 #27 6

Zn(H2O)6

+2 + OH- = Zn(H2O)5OH+ + H2O

Zn(H2O)6

+2 = Zn(H2O)5OH+ + H+

H2O = H+ + OH-

[ ]

] ][ [ ) (

2 1 − + +

= OH Zn OH Zn K

[ ][ ]

w

K K Zn H OH Zn K

1 2 1 *

] [ ) ( = =

+ + +

] ][ [

− +

= OH H Kw

Cumulative stability constants

 β describes the equilibrium between any given

complex and its component metal and ligands

 is the product of the successive K’s  Which describes the following equilibrium

David Reckhow CEE 680 #27 7

[ ]

2 2 2 2 1 2

] ][ [ ) (

− +

= = OH Zn OH Zn K K β

Zn(H2O)6

+2 + 2OH- = Zn(H2O)4(OH)2 + 2H2O

Cumulative stability constants (cont.)

 And *β is the form of β which is in terms of H+,

rather than OH-

 is the product of the successive *K’s  Which describes the following equilibrium  And:

David Reckhow CEE 680 #27 8

[ ][

]

] [ ) (

2 2 2 2 * 1 * 2 * + +

= = Zn H OH Zn K K β

Zn(H2O)6

+2 = Zn(H2O)4(OH)2 + 2H+

( )

2 2 2 * w

K β β =

Cumulative stability constants (cont.)

 So, in general:  And:

David Reckhow CEE 680 #27 9

[ ]

m n m n m m x x x m

OH Me OH Me K ] ][ [ ) (

) ( 1 − + − + = =

= =∏ β

[ ][ ]

] [ ) (

) ( 1 * * n m m n m m x x x m

Me H OH Me K

+ + − + = =

= =∏ β

To next lecture

David Reckhow CEE 680 #27 10