Ion colours

Question 1

Cu²⁺ (aq)

Answer 1

pale blue solution

Question 2

Cr³⁺

Answer 2

violet solution

Question 3

Fe²⁺

Answer 3

pale green solution

Question 4

Fe³⁺

Answer 4

yellow solution

Question 5

Mn²⁺

Answer 5

pale pink solution

Question 6

Cu²⁺ in OH-/NH3

Answer 6

• pale blue PPT
• [Cu(OH)₂(H₂O)₄]

Question 7

Cr³⁺ in OH-/NH3

Answer 7

• dark green PPT
• [Cr(OH)₃(H₂O)₃]

Question 8

Fe²⁺ in OH-/NH3

Answer 8

• Dark green PPT
• [Fe(OH)₂(H₂O)₄]

Question 9

Fe³⁺ in OH-/NH3

Answer 9

• orange-brown PPT
• [Fe(OH)₃(H₂O)₃]

Question 10

Mn²⁺ in OH-/NH3

Answer 10

• pale brown PPT
• [Mn(OH)₂(H₂O)₄]

Question 11

What are the 2 transition metals that change colour in excess NH3?

Answer 11

• Cu²⁺ is dark blue solution [Cu(NH3)₄(H₂O)₂]2+
• Cr³⁺ is a purple solution [Cu(NH3)₆]3+

Question 12

What is the only transition metal that changes colour in excess OH-?

Answer 12

Cr³⁺ becomes dark green solution [Cr(OH)₆]3-

Question 13

excess HCl + Cu2+

Answer 13

CuCl_{4 ^2-
yellow solution}

Question 14

Cu2+/ Cu

Answer 14

• disproportionation of Cu2+ forms brown solid (Cu) and blue solution (CuSO4)

Question 15

CoCl2.6H2O + excess HCl

Answer 15

CoCl₄ ^2-

blue

Question 16

Cr₂O₇ 2-

Answer 16

• from K₂Cr₂O₇ in 0.1 dm3- H₂SO₄
• orange

Question 17

CrO₄ 2-

Answer 17

• oxidation of Cr3+ w/ hot alkaline hydrogen peroxide
• yellow

Question 18

MnO₄-/Fe2+ to Mn2+/Fe3+ titration

Answer 18

-purple MnO₄- to pale pink Mn2+

Question 19

I-/ Fe3+ to I₂/ Fe 2+ titration

Answer 19

orange brown Fe3+ to brown I₂