Complex ion solution colours

Question 1

Cu²⁺ in aqueous solution

Answer 1

[ Cu(H₂O)₆]²⁺
Blue

Question 2

Fe²⁺ in aqueous solution

Answer 2

[ Fe(H₂O)₆]²⁺
Pale Green

Question 3

Fe³⁺ in aqueous solution

Answer 3

[ Fe(H₂O)₆]³⁺
Yellow/ brown

Question 4

Cr³⁺ in aqueous solution

Answer 4

[ Cr(H₂O)₆]³⁺
Violet

Question 5

Mn²⁺ in aqueous solution

Answer 5

[ Mn(H₂O)₆]²⁺
Pale pink

Question 6

Add some OH⁻ or NH₃ to [ Mn(H₂O)₆]²⁺

Answer 6

Mn(OH)₂(H₂O)₄
Pink Precipitate that turns brown on sitting

Question 7

Add some OH⁻ or NH₃ to [ Cu(H₂O)₆]²⁺

Answer 7

Cu(OH)₂(H₂O)₄
Pale blue precipitate

Question 8

Add some OH⁻ or NH₃ to [ Fe(H₂O)₆]²⁺

Answer 8

Fe(OH)₂(H₂O)₄
Dirty Green precipitate

Question 9

Add some OH⁻ or NH₃ to [ Fe(H₂O)₆]³⁺

Answer 9

Fe(OH)₃(H₂O)₃
Orange precipitate

Question 10

Add some OH⁻ or NH₃ to [ Cr(H₂O)₆]³⁺

Answer 10

Cr(OH)₃(H₂O)₃
Green - Grey precipitate

Question 11

Add excess NaOH to the precipitate

Answer 11

• No Change except Cr³⁺
  Cr(OH)₆³⁻
  Dark Green solution

Question 12

Add excess NH₃ to the precipitate

Answer 12

① [Cu(NH₃)₄(H₂0)₂]²⁺
Dark blue solution
②Cr(NH₃)₆³⁺
Purple solution
③ No change in the other precipitate