Chapter 24 - Transition Elements - COLOURS

colour of transition metal ions Cr₂O₇^2-

Cr₂O₇2- = orange

colour of transition metal ions VO₂+, VO²⁺

VO₂+ = yellow

VO2+ = blue

colour of transition metal ions Fe₂O_3, FeSO₄

Fe₂O₃ = yellow

FeSO₄ = pale green

colour of transition metal ions -written

manganese (II) sulfate = pink

titanium trichloride = purple

precipitation reaction

soluble ions are mixed together to produce an insoluble compound that settles out of solution = precipitate

ligand substitution reaction

a ligand in a complex ion is replaced by another ligand in a reaction

reactions of COPPER -aqueous copper(II) ions + HCl acid

-the 6 H2O ligands are replaced by 4 Cl ligands

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

pale blue solution + octahedral ⇌ yellow solution + tetrahedral

reactions of COPPER -aqueous copper(II) ions + little NH3

-NH3 accepts 2 protons from 2 of the H2O ligands in [Cu(H2O)6]2+

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

pale blue solution → blue precipitate

-forms hydrated copper(II) hydroxide

reactions of COPPER -hydrated copper(II) hydroxide + excess NH3

-4 NH3 ligands replace 2 OH- ligands and 2 H2O ligands

[Cu(OH)2(H2O)4] (s) + 4NH3 ⇌ [Cu(NH3)4(H2O)2]2+ (aq) + 2H2O + 2OH-

blue precipitate ⇌ deep blue solution

reactions of COPPER -aqueous copper(II) ions + excess NH3

-4 NH3 ligands replace 4 H2O ligands

[Cu(H2O)6]2+ (aq) + 4NH3 ⇌ [Cu(NH3)4(H2O)2]2+ (aq) + 4H2O

pale blue solution ⇌ deep blue solution

reactions of COPPER -aqueous copper(II) ions + NaOH

-2 OH- ions accept 2 protons from 2 H2O ligands

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

pale blue solution → blue precipitate

reactions of CHROMIUM -aqueous chromium(III) ions + little NH3

-NH3 accepts 3 protons from 3 of the H2O ligands in [Cr(H2O)6]3+

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

violet solution → green precipitate - octahedral

-forms hydrated chromium(III) hydroxide

reactions of CHROMIUM -hydrated chromium(III) ions + excess NH3

-6 NH3 ligands replace 3 OH- ligands and 3 H2O ligands

[Cr(OH)3(H2O)3] (s) + 6NH3 → [Cr(NH3)6]3+ (aq) + 3H2O + 3OH-

green precipitate → purple solution - octahedral

reactions of CHROMIUM -aqueous chromium(III) ions + excess NH3

-6 NH3 ligands replace 6 H2O ligands

[Cr(H2O)6]3+ (aq) + 6NH3 → [Cr(NH3)6]3+ (aq) + 6H2O

violet solution → purple solution - octahedral

reactions of CHROMIUM -aqueous chromium(III) ions + little NaOH

-chromium(III) hydroxide is insoluble in little NaOH

[Cr(H2O)6]3+ (aq) + 3OH- → [Cr(OH)3(H2O)3] (s) + 3H2O

violet solution → green precipitate

reactions of CHROMIUM -hydrated chromium(III) ions + excess NaOH

-3 OH- ligands replace 3 H2O ligands

[Cr(OH)3(H2O)3] (s) + 3OH- → [Cr(OH)6]3- (aq) + 3H2O

green precipitate → dark green solution

reactions of CHROMIUM -aqueous chromium(III) ions + excess NaOH

-6 OH- ligands replace 6 H2O ligands

[Cr(H2O)6]3+ (aq) + 6OH- → [Cr(OH)6]3- (aq) + 6H2O

violet solution → dark green solution

reactions of IRON(II) -aqueous iron(II) ions + NH3

-iron(II) hydroxide is insoluble in excess NH3 solution

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

pale green solution → green precipitate

reactions of IRON(II) -aqueous iron(II) ions + NaOH

-iron(II) hydroxide is insoluble in excess NaOH solution

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

pale green solution → green precipitate

reaction of IRON(III) -aqueous iron(III) ions + NH3

-iron(III) hydroxide is insoluble in excess NH3 solution

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

pale yellow solution → orange-brown precipitate

reaction of IRON(III) -aqueous iron(III) ions + NaOH

-iron(III) hydroxide is insoluble in excess NaOH solution

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

pale yellow solution → orange-brown precipitate

reaction of MANGANESE(II) -aqueous manganese(II) ions + NH3

-manganese(II) hydroxide is insoluble in excess NH3 solution

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

pale pink solution → light brown precipitate

reaction of MANGANESE(II) -aqueous manganese(II) ions + NaOH

-manganese(II) hydroxide is insoluble in excess NaOH solution

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

pale pink solution → light brown precipitate

OXIDATION of manganese (II) to (III)

4Mn(OH)2 (s) + O2 → 2MnO3 (s) + 4H2O

light brown precipitate → dark brown precipitate

REDOX reactions -oxidation of Fe2+ to 3+ → MnO4- to MN2+

MNO4- (aq) + 8H+ (aq) + 5Fe2+ (aq) → 5Fe3+ (aq) + Mn2+ (aq) + 4H2O (l)

purple solution → colourless/pale pink solution

half equations: MNO4- + 8H+ + 5e- → Mn2+ + 4H2O

5Fe2+ → 5Fe3+ + 5e-

Mn reduced from +7 to +2, Fe oxidised from +2 to +3

REDOX reactions -reduction of Fe3+ to Fe2+ → 2I- → I2

2Fe3+ (aq) + 2I- (aq) → 2Fe2+ (aq) + I2 (aq)

pale yellow solution → pale green solution + brown solution

half equations: 2Fe3+ + 2e- → 2Fe2+

2I- → I2 + 2e-

Fe reduced from +3 to +2, I oxidised from -1 to 0

REDOX reactions -oxidation of Cr3+ to CrO42- → H2O2

2Cr3+ + 3H2O2 + 10OH- → 2CrO42- + 8H2O

green solution → yellow solution

half equations: H2O2 + 2e- → 2OH-

8OH- + Cr3+ → CrO42- + 3e- + 4H2O

O reduced from -1 to -2, Cr oxidised from +3 to +6

REDOX reactions -reduction of Cr2O72- to Cr3+ → Zn

Cr2O7- + 14H+ + 3Zn → 2Cr3+ + 3Zn2+ + 7H2O

orange solution → green solution

half equations: Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O

3Zn → 3Zn2+ + 6e-

Cr reduced from +6 to +3, Zn oxidised from 0 to +2

REDOX reactions -reduction of Cu2+ to Cu+

2Cu2+ (aq) + 4I- (aq) → 2CuI (s) + I2 (aq)

pale blue solution → white precipitate + brown solution

half equations: 2Cu2+ + 2e- → 2Cu+

2I- → I2 + 2e-

Cu reduced from +2 to +1, I oxidised from -1 to 0

DISPROPORTIONATION of Cu+

Cu2O (s) + H2SO4 (aq) → Cu (s) + CuSO4 (aq) + H2O (l)

red solid → brown solid + pale blue solution

Cu reduced from +1 in Cu2O to O in Cu and oxidised from +1 in Cu2O to +2 in CuSO4