Colours of inorganic ions and complexes

Question 1

CuSO4.5H2O –> [Cu(H2O)6]2+

Answer 1

pale blue

Question 2

NH3 dropwise to Cu2+ –> Cu(OH)2

Answer 2

pale blue ppt

Question 3

excess NH3 to Cu2+ –> [Cu(NH3)4(H2O)2]2+

Answer 3

dark blue

Question 4

excess HCl to Cu2+ –> CuCl42–

Answer 4

yellow

Question 5

reduction of Cu2+ with I- –> Cu+

Answer 5

white precpitate (CuI)
and brown I2

Question 6

Disproportionation of Cu+ –> Cu2+/Cu

Answer 6

brown solid (Cu) and
blue solution (CuSO4)

Question 7

CoCl2.6H2O(s) plus H2O and excess HCl –> CoCl42–

Answer 7

blue

Question 8

KCr(SO4)2.12H2O –> [Cr(H2O)6]
3+

Answer 8

pale purple (heat green) Due to impurities, it is common for Cr(III) to appear green in solution

Question 9

NH3 dropwise to Cr3+ –> Cr(OH)3

Answer 9

dark green precipitate

Question 10

excess NH3 to Cr2+ –> [Cr(NH3)6]3+

Answer 10

purple

Question 11

excess OH– to Cr(OH) –> [Cr(OH)6]3–

Answer 11

dark green

Question 12

K2Cr2O7(s) in 0.1mol dm-3 H2SO4 –> Cr2O72–

Answer 12

orange

Question 13

oxidation of Cr3+ with hot alkaline H2O2 –> CrO42–

Answer 13

yellow

Question 14

MnSO4.4H2O –> [Mn(H2O)6]2+

Answer 14

pale pink

Question 15

NaOH dropwise to Mn2+ –> Mn(OH)2

Answer 15

pale brown ppt

Question 16

FeSO4.7H2O –> [Fe(H2O)6]2+

Answer 16

pale green

Question 17

NaOH dropwise to Fe2+ –> Fe(OH)2

Answer 17

dark green ppt

Question 18

FeCl3.6H2O –> [Fe(H2O)6]3+

Answer 18

yellow

Question 19

NaOH dropwise to Fe3+ –> Fe(OH)3

Answer 19

orange-brown precipitate

Question 20

MnO4–/Fe2+ –> Mn2+/Fe3+

Answer 20

purple to pale pink

Question 21

I–/Fe3+ –> I2/Fe2+

Answer 21

orange brown to brown