Transition metals ions colours

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[Cu(H₂O)₆]²⁺

from CuSO₄•5H₂O(s) pale blue

Cu(OH)₂(s)

NH₃ dropwise to Cu²⁺ (aq)  

pale blue precipitate 

[Cu(NH₃)₄(H₂O)₂]²⁺

excess NH₃ to Cu²⁺(aq)  

dark blue 

CuCl₄²⁻

excess HCl to Cu²⁺(aq)  

yellow 

Cu⁺

reduction of Cu²⁺ with I⁻  

white precipitate (CuI) and brown I₂ 

Cu²⁺/Cu

Disproportionation of Cu⁺  

brown solid (Cu) and blue solution (CuSO₄) 

CoCl₄²⁻

from CoCl₂•6H₂O(s) plus water and excess HCl  

blue 

[Cr(H₂O)₆]³⁺

from KCr(SO₄)₂•12H₂O(s) (heat → green)  Due to impurities, it’s common for Cr(III) to appear green in solution.

pale purple 

Cr(OH)₃(s)

NH₃ dropwise to Cr³⁺(aq)  

dark green precipitate 

[Cr(NH₃)₆]³⁺

excess NH₃ to Cr²⁺(aq)  

purple 

[Cr(OH)₆]³⁻

excess OH⁻ to Cr(OH)₃(s)

dark green 

Cr₂O₇²⁻

from K₂Cr₂O₇(s) in 0.1moldm⁻³ H₂SO₄

orange 

CrO₄²⁻

oxidation of Cr³⁺ w/ hot alkaline H₂O₂ 

yellow

[Mn(H₂O)₆]²⁺

from MnSO₄•4H₂O(s) 

pale pink 

Mn(OH)₂(s)

NaOH dropwise to Mn²⁺(aq)  

pale brown precipitate 

[Fe(H₂O)₆]²⁺

from FeSO₄•7H₂O(s) 

pale green 

Fe(OH)₂(s)

NaOH dropwise to Fe²⁺(aq) 

dark green precipitate 

[Fe(H₂O)₆]³⁺

from FeCl₃•6H₂O(s) 

yellow 

Fe(OH)₃(s)

NaOH dropwise to Fe³⁺(aq) 

orange-brown precipitate 

MnO₄⁻/Fe²⁺ → Mn²⁺/Fe³⁺

purple (MnO4₄⁻) to pale pink (Mn²⁺)  (in titrations, so dilute that it is practically colourless) 

I⁻/Fe³⁺ → I₂/Fe²⁺

orange brown (Fe³⁺) to brown (I₂)