Colours of Inorganic Ions and Complexes

What is the colour and formula of aqueous Cu²⁺?

[Cu(H2O)6]²⁺, pale blue

What forms when NH3 is added dropwise to Cu²⁺(aq)?

Cu(OH)₂(s), pale blue precipitate

What forms when excess NH3 is added to Cu2+(aq)?

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

What forms when excess HCl is added to Cu2+(aq)?

[CuCl4]2−, yellow solution

What happens when Cu2+ is reduced by I−?

CuI(s) white precipitate and brown I2

What happens to Cu+ in aqueous solution?

Disproportionates to Cu(s) and Cu2+(aq)

What is the colour and formula of aqueous Co2+ with excess Cl−?

[CoCl4]2−, blue

What is the colour and formula of aqueous Cr3+?

[Cr(H2O)6]3+, pale purple (often green due to impurities)

What forms when NH3 is added dropwise to Cr3+(aq)?

Cr(OH)3(s), dark green precipitate

What forms when excess NH3 is added to Cr3+(aq)?

[Cr(NH3)6]3+, purple

What forms when excess OH− is added to Cr(OH)3(s)?

[Cr(OH)6]3−, dark green solution

What is the colour of dichromate(VI) ions?

Cr2O7^2−, orange

How are chromate(VI) ions formed from Cr3+?

Oxidation with hot alkaline H2O2, CrO4^2− yellow

What is the colour and formula of aqueous Mn2+?

[Mn(H2O)6]2+, pale pink

What forms when NaOH is added dropwise to Mn2+(aq)?

Mn(OH)2(s), pale brown precipitate

What colour change occurs for MnO4− in redox reactions?

Purple to pale pink Mn2+ (nearly colourless when dilute)

What is the colour and formula of aqueous Fe2+?

[Fe(H2O)6]2+, pale green

What forms when NaOH is added dropwise to Fe2+(aq)?

Fe(OH)2(s), dark green precipitate

What is the colour and formula of aqueous Fe3+?

[Fe(H2O)6]3+, yellow

What forms when NaOH is added dropwise to Fe3+(aq)?

Fe(OH)3(s), orange-brown precipitate

What colour change occurs when Fe3+ reacts with I−?

Orange-brown Fe3+ to brown I2