Transition Metals Reactions

Name the 5 transition metal ions and their colours in solution

Cu²⁺ - blue
Cr³⁺ - green
Fe²⁺ - pale green
Fe³⁺ - yellow
Mn²⁺ - pale pink

What are the colours of the 5 transition metal hydroxide precipitates?

Cu(OH)₂ - blue
Cr(OH)₃ - grey/green
Fe(OH)₂ - green
Fe(OH)₃ - orange/brown
Mn(OH)₂ - light brown

Which metal hydroxides change colour on standing with air? Give reasons if necessary

Fe(OH)₂ turns from green to orange/brown at the surface (Fe²⁺ oxidises to Fe³⁺)
Mn(OH)₂ darkens on standing in air

What happens if excess NaOH is added to Cr(OH)₃? Give an equation

Cr(OH)₃ precipitate redissolves to form a dark green solution of [Cr(OH)₆]³⁻
Cr(OH)₃(s) + 3OH⁻(aq) → [Cr(OH)₆]³⁻(aq)

What happens if excess NH₃ is added to Cu(OH)₂? Give full complex equation

Cu(OH)₂ precipitate redissolves to form dark blue solution of [Cu(NH₃)₄(H₂O)₂]²⁺
[Cu(H₂O)₆]²⁺(aq) + 4NH₃(aq) → [Cu(NH₃)₄(H₂O)₂]²⁺(aq) + 4H₂O(l)

What happens if excess NH₃ is added to Cr(OH)₃? Give full complex equation

Cr(OH)₃ precipitate redissolves to form purple solution of [Cr(NH₃)₆]³⁺
[Cr(H₂O)₆]³⁺(aq) + 6NH₃(aq) → [Cr(NH₃)₆]³⁺(aq) + 6H₂O(l)

What happens if Cl⁻ ions are added to Cu²⁺ solution? Give full complex equation

-Ligand substitution
-Colour change from blue to yellow
[Cu(H₂O)₆]²⁺ + 4Cl⁻ → [CuCl₄]²⁻ + 6H₂O

What reagents are used to oxidise Fe²⁺ to Fe³⁺? What is the colour change?

acidified potassium manganate (VII) solution, H⁺/MnO₄⁻
pale green to yellow

What reagents are used to reduce Fe³⁺ to Fe²⁺? What is the colour change?

iodide ions, I⁻
yellow to pale green

What reagents are used to oxidise Cr³⁺ to Cr₂O₇²⁻? What is the colour change?

warm hydrogen peroxide in alkaline conditions, H₂O₂/OH⁻
green to orange

What reagents are used to reduce Cr₂O₇²⁻ to Cr³⁺? What is the colour change?

acidified zinc, Zn/H⁺
orange to green

What reagents are used to reduce Cu²⁺ to Cu⁺? What is the colour change?

iodide ions, I⁻
blue solution to off-white precipitate of CuI

What happens to Cu⁺ in solution?

Spontaneously disproportionates into Cu²⁺(aq) and Cu(s)