Ligand substitution and precipitation reactions

Cu2+, observation with NaOH

Blur gelatinous precipitate

Cu2+ with NaOH equation

[Cu(H2O)6]2+(aq) + 20H(aq) → [Cu(OH)2(H2O)4](s) + 2H2O

colour of [Cu(H2O)4(OH)2]

blue gelatinous

Cu observation with ammonia

Blue gelatinous precipitate, redissolves into blue solution

Equation Cu 2+ with NH3

[Cu(H2O)6]2+(aq) + 2NH3(aq) → [Cu(OH)2(H2O)4](s) + 2NH4+(aq)

Observation Cu2+ with hydrochloric acid

Pale blur to green to yellow solution in equib

colour of [Cu(H2O)6]2+

pale blue

colour of [CuCl4]2-

yellow

Cu 2+ with hydrochloric acid equation

[Cu(H2O)6]2+(aq) + 4Cl-(aq) → [CuCl4](aq) + 6H2O(l)

Fe2+ observation with NaOH

Pale green solution containing Fe2+(aq) forms a green precipitate, turning a rusty brown at its surface on standing in air

Fe 2+ with NaOH equation

Fe2+(aq) + 20H (aq) → Fe(OH)2(s)

colour of Fe(OH)2

green

colour of Fe(OH)3

rusty brown

Fe2+ with ammonia observation

Dark green precipitate formed

Fe2+ with ammonia equation

[Fe(H2O)6]2+(aq) + 2NH3(aq) → [Fe(OH)2(H2O)4] (s) + 2NH4+(aq)

colour of [Fe(OH)2(H2O)]

dark green

Fe3+ observation with NaOH

Pale yellow solution containing Fe3+(aq) forms a rusty brown precipitate (iron(III) hydroxide)

Fe 3+ with NaOH equation

Fe3+(aq) + 30H- (aq) → Fe(OH)3(s)

colour of aqueous fe 3+

yellow

Fe3+ with ammonia observation

Rusty brown precipitate formed

Fe3+ with ammonia equation

[Fe(H2O)6]3+(aq) + 3NH3(aq) → [Fe(OH)3(H2O)3](s) + 3NH4+(aq)

Mn2+ with NaOH observation

Brown precipitate forms, which darkens in air as it oxidises

Mn2+ with NaOH equation

[Mn(H2O)6]2+(aq) + 20H (aq) → [Mn(OH)2(H2O)4] (s) + 2H2O

The manganese ion can be summarised to Mn(OH)2. Oxidation can be summarised by:

4Mn(OH)2 + O2 ← 2Mn2O3 + 4H20

colour Mn(OH)2

brown

colour if Mn2O3

darker brown

Mn2+ with ammonia observation

Brown precipitate forms, which darkens in air as it oxidises

Mn2+ with ammonia equation

[Mn(H2O)6]2+(aq) + 2NH3(aq) - [Mn(OH)2(H2O)4] (s) + 2NH4+(aq)

Cr3+ with NaOH observation

Green precipitate formed then redisdolves in excess hydroxide

Cr3+ with NaOH equation

[Cr(H2O)613+(aq) + 30H(aq) → [Cr(OH)3(H2O)3](S) + 3H2O Then [Cr(OH)3(H2O)3](S) + 30H (aq) → [Cr(OH)6]3-(aq) + 3H20

colour of CrOH3

green that redissolves

Cr3+ with ammonia observation

Green precipitate formed which redissolves if excess ammonia is added

Cr3+ with ammonia equation