Chapter 24: Complex Ion Colour Changes

Question 1

[Cu(H2O)6]2+
Colour

(From CuSO4 : 5H2O (s))

Answer 1

Pale blue

Question 2

Cu(OH)2 (s)

Colour
(From NH3 dropwise to Cu2+)

Answer 2

Pale blue PPT

Question 3

[Cu(NH3)4(H2O]2+

Colour
(From excess NH3 to Cu2+ (aq))

Answer 3

Dark blue

Question 4

CuCl4 2-

Colour
(Excess HCL to Cu2+ (aq))

Answer 4

Yellow

Question 5

Cu+

Colour
(Reduction of Cu2+ with I-)

Answer 5

White PPT (CuI) and brown I2

Question 6

Cu2+/ Cu

Colour?
(Disproportionating of Cu+)

Answer 6

Brown solid (Cu) and blue solution (CuSO4)

Question 7

CoCl4 2-

Colour?
(From CoCl2 : 6H2O (s) and water, excess HCl)

Answer 7

Blue

Question 8

[Cr(H2O)6]3+

Colour?
(From KCr(SO4)2 : 12H2O (s))

And Heat to ….

Answer 8

Pale purple

However due to impurities common for Cr(III) to appear green in solution

Question 9

Cr(OH)3 (s)

Colour?
(From NH3 dropwise to Cr3+)

Answer 9

Dark green PPT

Question 10

[Cr(NH3)6]3+

Colour?
(Excess NH3 to Cr2+)

Answer 10

Purple

Question 11

[Cr(OH)6]3-

Colour?
(Excess OH- to Cr(OH)3 (s))

Answer 11

Dark green

Question 12

Cr2O7 2-

Colour?
(From K2CR2O7 (s) in 1 mol dm^-3 H2SO4)

Answer 12

Orange

Question 13

CrO4 2-

Colour?
(Oxidation of Cr3+ with hot alkaline H2O2)

Answer 13

Yellow

Question 14

[Mn(H2O)6]2+

Colour?
(From MnSO4 : 4H2O (s))

Answer 14

Pale pink

Question 15

Mn(OH)2 (s)

Colour?
(NaOH dropwise to Mn2+ (aq))

Answer 15

Pale brown PPT

Question 16

[Fe(H2O)6]2+

Colour?
(From FeSO4 : 7H2O (s))

Answer 16

Pale green

Question 17

Fe(OH)2 (s)

Colour?
(NaOH dropwise to Fe2+ (aq))

Answer 17

Dark green PPT

Question 18

[Fe(H2O)6]3+

Colour?
(From FeCl3 : 6H2O (s)

Answer 18

Yellow

Question 19

Fe(OH)3 (s)

Colour?
(NaOH dropwise to Fe3+ (aq))

Answer 19

Orange-brown PPT

Question 20

MnO4-/ Fe2+ —> Mn2+/ Fe3+

Colour change?

Answer 20

Purple (MnO4-) to pale pink (Mn2+)

In titrations so dilute that it is practically colourless

Question 21

I-/ Fe3+ —> I2/ Fe2+

Colour change?

Answer 21

Orange brown (Fe3+) to brown (I2)