3.2.6 reactions of ions in aq solutions

Question 1

Hydrated ( metal- aqua ) complexes

Answer 1

• Metal - aqua complexes are formed added to a transition metal compound to water
• 6 water molecules form bonds with metal ion - cause lone pair on oxygen
• complexes written as Cu[(H20)6]2+ / Fe[(H20)6]3+

Question 2

Acidic metal aqua complexes

Answer 2

• metal - aqua Ions are acidic in solution - charge of the ion has effect on how acidic it is
• [Fe(H20)6]2+ + H20 <=> [Fe(H20)5(OH)]+ + H3O+
• hydroxonium produced - reaction hydrolysis, 2+ complex ions dissociate weakly - not acidic
• for 3+ complex - dissociate more rapidly then 2+ - more acidic ( higher charge density - small/large charge - more polarising - attract oh bond more strongly- weekend bonds. - H+ more likely to be released

Question 3

Further hydrolysis of metal-aqua ions

Answer 3

• • hydrolyse further OH- ions make insoluble metal hydroxides
• further hydrolysis- new equilibrium- OH- ions remove H30+ ions - equilibrium shifts to right
• more hydrolysis- formation of neutral complex- solid / precipitate
• process with 2+(2step) , 3+( 3 step) - each step a OH is removed from h20 - product charge decreases whilst OH increase

Question 4

Amphoteric metal hydroxides

Answer 4

• • metal hydroxides- as acid and base ( amphoteric)
• dissolve in both excess base and acid
• reverse by adding H+ to precipitate- dissolve - (Al(H20)3(OH)3) - aluminium hydroxide - add base - acts as Brønsted-Lowry acid / donated H+ ions and acf as Brønsted-Lowry base / accepting H+ ions form H30+

Question 5

Metal-aqua ions and ammonia

Answer 5

• ammonia + metal aqua ions- metal hydroxides precipitate-sometimes adding excess ammonia- ligand exchange reaction
• small NH3 added- equilibrium ( NH3 + H2O <=> NH4+ +OH-
• excess ammonia - get partial ligand substitution- displaced , charged soluble complex formed with Cu(OH)2(H20)4