Transition metal hydroxide precipitates

Question 1

Turning chromium (iii) water complex to hydroxide ppt
(Acid base)

Answer 1

[Cr(H2O)6]3+(aq) + 3OH-(aq) -> Cr(H2O)3(OH)3 + 3H2O(l)

Question 2

Turning cobalt (ii) water complex to hydroxide ppt
(Acid base)

Answer 2

[Co(H2O)6]2+(Aq) +3OH-(aq) -> Fe(H2O)4(OH)2 + 2H2O(l)

Question 3

Reaction of transition metal ions in aqueous solutions with NH3 (NH4OH)

Answer 3

Drop wise addition
Same number of NH3 molecules added as charge on ligand
Forms OH- in complex ppt and NH4+ Solution

Question 4

[Cr(H2O)6]3+ (aq) + 3NH3(aq)

Answer 4

forms
Cr(H2O)3(OH)3 + 3NH4+

Question 5

[Fe(H2O)6]2+(aq) +2NH3(aq)

Answer 5

Forms
Fe(H2O)4(OH-)2 + 2NH4+(aq)

Question 6

Reaction of metal hydroxides with NaOH

Answer 6

Addition of excess
Rests with amphoteric metal hydroxides e.g. chromium (iii) hydroxide
First the ppt dissolves and then acid base reaction can occur. These reactions can bre reversed by using an acid

Question 7

Dissolving chromium (iii) hydroxide ppt

Answer 7

Green ppt to green solution

Cr(H2O)3(OH)3 +OH-(aq) -> [Cr(H2O)2(OH)4]-(aq) +H2O(l)

Question 8

Further acid base reaction (deprotination) of [Cr(H2O)2(OH-)4]-

Answer 8

no colour change (green solution)
[Cr(H2O)2(OH)4]- +2OH-(aq) -> [Cr(OH)6]3-(aq) +2H2O(l)

Question 9

Overall equation for adding OH- to [cr(h2O)3

Answer 9

[Cr(H2O)3(OH)] +3OH- -> [Cr(OH)6]3- +3H2O

Question 10

Ligand exchange reactions

Answer 10

Occur when excess ammonia is added
Only occurs for some of the transition metal hydroxides (cobalt and copper)
NH3 replaces H2O in complex

Question 11

Ligand exchange
Cr(H2O)3(OH)3 + 6NH3(aq)

Answer 11

Forms
[Cr(NH3)6]3+(aq) +3OH- +3H2O(l)
Green ppt to violet solution (partially soluble)

Question 12

Ligand exchange
Co(H2O)4(OH)2 + 6NH3(aq)

Answer 12

Forms
[Co(NH3)6]2+(Aq) + 2OH-(aq) +4H2O(l)
Blue ppt to brown solution (darkens over time)

Question 13

Ligand exchange
Cu(H2O)4(OH)2 + 4NH3(aq)

Answer 13

[Cu(NH3)4(H2O)2]2+(aq) + 2OH- (aq) +2H2O (l)
Blue ppt to dark brown solution