Transition metal colours

Question 1

Cr3+ (aq)

Answer 1

Violet solution

Question 2

Fe2+ (aq)

Answer 2

Green solution

Question 3

Fe3+ (aq)

Answer 3

Yellow solution

Question 4

Mn2+ (aq)

Answer 4

Pale pink solution

Question 5

Cu2+ (aq)

Answer 5

Blue solution

Question 6

What is the trick for remembering the formulas of precipitates when metal ion complexes are reacted with OH- or NH3?

Answer 6

The number of OH- or NH3 substituted is the same as the value of the charge on the initial ion.

Question 7

Cr3+ with OH-

Answer 7

Green precipitate

Question 8

Fe2+ with OH-

Answer 8

Green precipitate

Question 9

Fe3+ with OH-

Answer 9

Brown precipitate

Question 10

Mn2+ with OH-

Answer 10

Pale brown precipitate

Question 11

Cu2+ with OH-

Answer 11

Blue precipitate

Question 12

Which metal ion further reacts with an excess of OH- ions?

Answer 12

Cr3+

Question 13

Cr3+ with excess OH-

Answer 13

Green solution [Cr(OH)6]3-

Question 14

Cr3+ with NH3

Answer 14

Green precipitate

Question 15

Fe2+ with NH3

Answer 15

Green precipitate

Question 16

Fe3+ with NH3

Answer 16

Brown precipitate

Question 17

Mn2+ with NH3

Answer 17

Pale brown precipitate

Question 18

Cu2+ with NH3

Answer 18

Blue precipitate

Question 19

Which metal ions further react with excess NH3?

Answer 19

Cr3+ and Cu2+

Question 20

Cr3+ with excess NH3

Answer 20

Purple solution [Cr(NH3)6]3+

Question 21

Cu2+ with excess NH3

Answer 21

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

Question 22

[CuCl4]2-

Answer 22

Yellow solution

Question 23

What colour may [CuCl4]2- look when made from Cu2+ and HCl and why?

Answer 23

May look green. Reversible reaction. Both blue and yellow species present.