Transition Metal Colours

Question 1

[Cu(H2O)6]2+ + NaOH/NH3 = ?

Answer 1

Cu(OH)2(s) pale blue ppt

Question 2

[Cu(H2O)6]2+ add excess ammonia
What type of reaction is this?

Answer 2

[Cu(NH3)4(H2O)2]2+ Dark blue

This is a ligand substitution reaction

Question 3

[Cu(H2O)6]2+ + conc. HCl

What kind of reaction is this

Answer 3

CuCl 2-
Yellow

Ligand substitution reaction

Question 4

[Mn(H2O)6]2+ + NaOH/NH3

Answer 4

Mn(OH)2 brown ppt

Question 5

[Mn(H2O)6]2+ in air

Answer 5

Mn(OH)3 (s)
Darker brown precipitate

Question 6

[Fe(H2O)6]2+ + NaOH/NH3

Answer 6

Fe(OH)2 dark green ppt

Question 7

[Fe(H2O)6]2+ in air

Answer 7

Fe(OH)3 Orange brown ppt

Question 8

[Fe(H2O)6]3+ + NaOH/NH3

Answer 8

Fe(OH)3
Orange brown ppt

Question 9

[Cr(H2O)6]3+ + NaOH/NH3

Answer 9

Cr(OH)3 dark green ppt

Question 10

[Cr(H2O)6]3+ excess NaOH

Answer 10

[Cr(OH)6]3-
Dark green

Question 11

[Cr(H2O)6]3+ in excess NH3

Answer 11

[Cr(NH3)6]3-
Purple

Question 12

I-/Fe3+ to I2/Fe2+

Answer 12

Reduction of Fe3+ to Fe2+
Orange to brown colour change

Question 13

MnO4-/Fe2+ to Mn2+/Fe3+

Answer 13

Oxidation of Fe2+ to Fe3+
Purple to pink

Question 14

I-/Cu2+ to I2/Cu+

Answer 14

Reduction of Cu2+ to Cu +

Pale blue to brown solution & white ppt

2CU2+ + 2I- TO I2 CuI

Question 15

H202/Cr3+ to H20/CrO4 2-

Answer 15

Green to yellow
Hot aqueous alkaline oxidises Cr3+

Question 16

Cr2O7+ / H+ / Zn to Cr3+ / Zn2+ to Zn/Cr2+

Answer 16

Orange to green to pale blue

Excess zinc reduces Cr3+ to Cr 2+

Question 17

H+/Cu+ to H2O / Cu2+ / Cu

Answer 17

Product is blue solution (CuSO4) and brown solid (Cu)