transition metal colours

Question 1

[Cu(H2O)6]2+
(from CuSO4•5H2O)

(Cu2+)

Answer 1

pale blue

Question 2

Cu(OH)2 (s)
(when NH3 is added drop wise)

(Cu2+)

Answer 2

pale blue precipitate

Question 3

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

EXCESS NH3 to Cu2+

Answer 3

dark blue

Question 4

[CuCl4]2-

EXCESS HCl added to Cu2+

Answer 4

yellow

Question 5

Cu+

reduction of Cu2+ with I-

Answer 5

white precipitate (CuI)
brown I2

Question 6

Cu2+/Cu

disproportionation of Cu+

Answer 6

brown solid (Cu)
blue solution (CuSO4)

Question 7

[CoCl4]2-

from CoCl2•6H2O + H2O + excess HCl

Answer 7

blue

Question 8

[Cr(H2O)6]3+
from KCr(SO4)2•12H2O
what colour with heat?

Answer 8

pale purple
heat —-> green
due to impurities it is common for Cr(III) to appear green in solution

Question 9

Cr(OH)3

NH3 added dropwise to Cr3+

Answer 9

grey green precipitate

Question 10

[Cr(NH3)6]3+

excess NH3 added to Cr3+

Answer 10

purple

Question 11

[Cr(OH)6]3-

excess OH- added to Cr(OH)3

Answer 11

dark green solution

Question 12

Cr2O7 2-

from K2Cr2O7 in H2SO4

Answer 12

orange

Question 13

CrO4 2-

ocidation of Cr3+ with hot alkaline H2O2

Answer 13

yellow

Question 14

[Mn(H2O)6]2+

from MnSO4•4H2O

Answer 14

pale pink

Question 15

Mn(OH)2

NaOH added dropwise to Mn2+

Answer 15

pale brown precipitate

Question 16

[Fe(H2O)6]2+

from FeSO4•7H2O

Answer 16

pale green

Question 17

Fe(OH)2

NaOH added dropwise to Fe2+

Answer 17

dark green precipitate

Question 18

[Fe(H2O)6]3+

from FeCl3•6H2O

Answer 18

yellow

Question 19

Fe(OH)3

NaOH added dropwise to Fe3+

Answer 19

orange brown precipitate

Question 20

MnO4- / Fe2+ —————> Mn2+ / Fe3+

Answer 20

MnO4- : purple

Mn2+ : pale pink

Question 21

I- / Fe3+ —————> I2 / Fe2+

Answer 21

orange brown to brown

Question 22

Co2+

Answer 22

pink