Complex Ion Solutions and Ppts Colours

Question 1

Describe the colour change and new compound/complex ion when you add OH- to [Cu(H2O)6]2+

Answer 1

Goes from blue solution to blue ppt

Product: [Cu(H2O)4(OH)2]

Question 2

Describe the colour change and new compound/complex ion formed when you add excess NH3 to [Cu(H2O)6]2+

Answer 2

Goes from a blue solution to a deep blue solution

Product: [Cu(NH3)4(H2O)2]2+

Question 3

Describe the colour change and resulting compound when you add OH- to [Fe(H2O)6]2+

Answer 3

Goes from a green solution to a green ppt

Product: [Fe(H2O)4(OH)2]

Question 4

Describe the colour change and resulting compound when you add excess NH3 to [Fe(H2O)6]2+

Answer 4

No change. Stays as a green solution

Product: none

Question 5

Describe the colour change and the resulting compound when you add OH- to [Cr(H2O)6]3+

Answer 5

Goes from a violet solution to a green ppt

Product: [Cr(H2O)3(OH)3]

Question 6

Describe the colour change and resulting compound when you add excess NH3 to [Cr(H2O)6]3+

Answer 6

Goes from a violet solution to a purple solution

Product: [Cr(NH3)6]3+

Question 7

Describe the colour change and resulting compound when you add OH- to [Fe(H2O)6]3+

Answer 7

Goes from yellow solution to brown ppt

Product: [Fe(H2O)3(OH)3]

Question 8

Describe the colour change and resulting compound when you add excess NH3 to [Fe(H2O)6]3+

Answer 8

The solution remains yellow, nothing happens.

Question 9

Describe the colour change and resulting compound when you add OH- to [Mn(H2O)6]2+

Answer 9

Goes from pale pink solution to a light brown ppt

Product: [Mn(H2O)4(OH)2]

Question 10

Describe the colour change and resulting compound when you add excess NH3 to [Mn(H2O)6]2+

Answer 10

Nothing happens, it remains as a pale pink solution

Question 11

What happens if Fe(OH)2 stands in air?

Answer 11

It turns into Fe(OH)3, and goes from a green ppt to an orange-brown ppt

Question 12

What happens to each of the following compounds when you add excess NaOH to them?
Cu(OH)2
Fe(OH)2
Mn(OH)2
Fe(OH)3
Cr(OH)3

Answer 12

None of them change except Cr(OH)3 (green ppt). This becomes [Cr(OH)6]3-, which is a dark green solution.

Question 13

What happens to Fe2+ if you add excess aq ammonia?

Answer 13

Becomes Fe(OH)2(s), which is a green ppt.
Does not dissolve in excess aq ammonia

Question 14

What happens to Fe3+ when you add excess aq ammonia?

Answer 14

Turns into Fe(OH)3, an orange brown ppt (Fe3+ is a pale yellow solution)
Does not dissolve in excess ammonia

Question 15

What happens to Mn2+ if you add excess aq ammonia?

Answer 15

Goes from a pale pink solution to a light brown ppt of Mn(OH)2
Does not dissolve in excess ammonia

Question 16

What happens if you add concentrated HCl to a solution of [Cu(H2O)6]2+?

Answer 16

It goes from a pale blue solution, to a yellow solution of [CuCl4]2- (and gives out 6 H2O from this ligand substitution reaction).
Only 4 chloride ions can fit around Cu2+ because they are much larger ligands than H2O, so less Cl can fit around Cu than H2O.

Question 17

What happens if you dissolve chromium(III) sulfate in water?

Answer 17

You get a green solution of [Cr(H2O)5SO4]+

This does contain Cr with oxidation state of +3

Question 18

What happens if you dissolve chrome alum ( KCr(SO4)2•12(H2O)/chromium(III) potassium sulfate) in water?

Answer 18

You get a pale purple solution of [Cr(H2O)6]3+

Question 19

What happens when you dissolve copper(II) sulfate in water?

Answer 19

The pale blue solution [Cu(H2O)6]2+ is formed