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

Print version 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

 O Elemental abundance in crust  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: 3d 10 , 4s 2 (like Mg: 3s 2 )  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 [ ][ ] + + Zn ( OH ) H  First step = * K +2 = Zn(H 2 O) 5 OH + + H +  Zn(H 2 O) 6 1 + 2 [ Zn ]  Second step  Zn(H 2 O) 5 OH + = Zn(H 2 O) 4 (OH) 2 0 + H + [ ] + Zn ( OH ) [ H ] = * K 2 2 + [ ZnOH ] David Reckhow CEE 680 #27 4

Hydrolysis (cont.)  Zinc example expressed as hydroxide formation  First step +2 + OH - = Zn(H 2 O) 5 OH + + H 2 O  Zn(H 2 O) 6 [ ] + Zn ( OH ) = K 1 + − 2 [ Zn ][ OH ]  Second step  Zn(H 2 O) 5 OH + + OH - = Zn(H 2 O) 4 (OH) 2 0 + H 2 O [ ] Zn ( OH ) = K 2 2 + − [ ZnOH ][ OH ] David Reckhow CEE 680 #27 5

Hydrolysis (cont.)  Converting between the two forms [ ] + Zn ( OH ) +2 + OH - = Zn(H 2 O) 5 OH + + H 2 O = K Zn(H 2 O) 6 1 + − 2 [ Zn ][ OH ] H 2 O = H + + OH - + − = K w [ H ][ OH ] [ ][ ] +2 = Zn(H 2 O) 5 OH + + H + Zn(H 2 O) 6 + + Zn ( OH ) H = * K 1 + 2 [ Zn ] = K K 1 w David Reckhow CEE 680 #27 6

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 [ ] Zn ( OH ) β = = K K 2 2 1 2 + − 2 2 [ Zn ][ OH ]  Which describes the following equilibrium +2 + 2OH - = Zn(H 2 O) 4 (OH) 2 + 2H 2 O Zn(H 2 O) 6 David Reckhow CEE 680 #27 7

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 ] [ ] [ 2 + Zn ( OH ) H β = = * * * 2 K K 2 1 2 + 2 [ Zn ]  Which describes the following equilibrium +2 = Zn(H 2 O) 4 (OH) 2 + 2H + Zn(H 2 O) 6  And: ( ) 2 β = β * K 2 2 w David Reckhow CEE 680 #27 8

Cumulative stability constants (cont.)  So, in general: [ ] + − = ( n m ) x m Me ( OH ) = ∏ β = m K m x + − n m [ Me ][ OH ] = x 1  And: [ ][ ] m + − + = ( n m ) x m Me ( OH ) H = ∏ β = * * K m m x + n [ Me ] = x 1 David Reckhow CEE 680 #27 9

 To next lecture David Reckhow CEE 680 #27 10