Lecture 14 2/21/07

Metal hydrolysis

Heavy metals as Lewis acids

Fe(H2O)63+ (aq) ⇆ Fe(H2O)5(OH) 2+ (aq) + H+ (aq)

Fe(H2O)62+ (aq) ⇆ Fe(H2O)5(OH)

+ (aq) + H+ (aq)

Amphoteric metals (Al3+, Cr3+, Zn2+, Sn4+)

Al(H2O)3(OH)3 (s) - insoluble

Al(H2O)3(OH)3 (s) + OH- → Al(H2O)2(OH)4- (aq) + H2O

Al(H2O)3(OH)3 (s) + H3O+ → Al(H2O)4(OH)2+ (aq) +

H2O

Table 16-5, p.800

How does changing pH affect solubility?

Mg(OH)2(s) ⇄ Mg2+ (aq) + 2OH- (aq)

CaCO3 (s) ⇄ Ca2+ (aq) + CO32- (aq)

AgCl (s) ⇄ Ag+ (aq) + Cl- (aq)

Determine the maximum concentration of Mn2+ in a solution with a pH = 11.15.

Ksp = 4.6 x 10-14

Molecular structure and acid strength

Why do some compounds donate H+ and some don’t?

All acidic H bonds are polar bonds

Binary AcidsWithin group:

Across Row:

Molecular structure and acid strength

Molecular structure and acid strength

H-O-Z

HOCl HOBr HOI

Ka 3.5 x 10-8 2.5 x 10-9 2.3 x 10-11

electronegativity Cl (3.0) Br (2.8) I (2.5)

Oxoacids with different central atoms