INDIVIDUAL TRANSITION ELEMENTS

Vanadium
[V(H2O)6]2+ +2 violet
[V(H2O)6]3+ +3 green
[VO(H2O)5]2+ +4 blue
[VO2(H2O)4]+ +5 yellow
VO3- +5 colourless (in alkaline) (in acid: VO3- > [VO2(H2O)4]+)
V4+, V5+: exist as oxo-anions (not as free ions) (V cov bond w/ O)
all ions octahedral except VO3-
[VO(H2O)5]2+
[VO2(H2O)4]+

uses:
-alloying:
  + steel > harder (due to Vn hardness & tensile strength) (exhaust valves, high-speed tools)
  + Cr: springs
  + Ti: missiles, jet engines, in nulcear reactors
-catalyst (Contact process- V2O5)

Chromium
+6 dichromate(VI), Cr2O72- orange (oxidising)
+6 chromate(VI), CrO4- yellow (oxidising)
+3 chromium(III), Cr3+ green (most stable)
+2 chromium(II), Cr2+ blue (reducing)
ZnHg / Zn: reduces Cr2O72- > Cr3+ > Cr2+ (orange > green > blue)

+3: violet in presence of SO42- / alum: heat > green (partial replaement of water molecule by other ligands)
[Cr(H2O)6]3+(aq) + SO42-(aq) > [Cr(H2O)5SO42-]+(aq) + H2O(l)

Cr3+(aq): acidic due to high charge and small size (polarisation)
in water: [Cr(H2O)6]3+(aq) + H2O(l) > [Cr(H2O)5OH]2+(aq) + H3O+(aq)
in NaCO3:
  [Cr(H2O)5OH]2+(aq) + H2O(l) > [Cr(H2O)4(OH)2]+(aq) + H3O+(aq)
  [Cr(H2O)4(OH)2]+(aq) + H2O(l) > [Cr(H2O)3(OH)3](aq) + H3O+(aq)


add basic species (CO32-) > Cr(OH)3(s) as H3O+ removed

[Cr(H2O)6]3+(aq) + 3OH-(aq) > Cr(OH)3(s) + 6H2O(l)
Cr(OH)3(s), green ppt, sol in xs NaOH: Cr(OH)3(s) + OH-(aq) > Cr(OH)63-(aq) (dark green)

+6
CrO4-: yellow
Cr2O72-: green
CrO4- + acid > Cr2O72- (yellow > green)
2CrO4- + H+ > Cr2O72- + H2O
Cr2O72- + alkali > CrO4- (green > yellow)
Cr2O72- + OH- > 2CrO4- + H2O

Cr2O72-: strong oxidising agent
Cr2O72- + 14H+ + 6e- > 2Cr3+ + 7H2O, = +1.33V
isomerism
hydrate isomers: CrCl3(H2O)6:
  [Cr(H2O)4Cl2]+.Cl-.2H2O: dark green solid
  [Cr(H2O)5Cl]2+.2Cl-.H2O: light green solid
  [Cr(H2O)6]3+.3Cl-: violet solid
can be identified by AgNO3 (mass of ppt)
geometric: [Cr(NH3)4Cl2]
optical:
  -tri(ethandioate) chromate(III) anions, [Cr(-OC=OC=OO-)3]3-
  -tri(ethane-1,2-diamine) chromium(III) cations, [Cr(N-N)3]3+ [(N-N): H2NCH2CH2NH2]
Uses:
  -alloying (w/ Fe, Ni, Co) (due to hardness, tensile strength & resistance to corrosion) (stainless steel- Fe, 18% Ni, 8% Cr) (Cr, Co, tungsten- high speed cutting tools)
  -electroplating (hard, resistant to corrosion, lustrous - vehicles)
Manganese
+2 Mn2+, manganese(II) ion pale pink (colourless)
+3 Mn3+, manganese(III) ion dark red
+4 Mn2+, manganese(IV) oxide black (dark brown)
+5 MnO43-, manganate(V) ion blue
+6 MnO42-, manganese(VI) ion green
+7 MnO4-, manganese(VII) ion purple
MnO4-: powerful oxid agent (oxid power dpd on pH)
in acid: MnO4- + 8H+ + 5e- > Mn2+ + 4H2O, =+1.52V
in alkaline: MnO4- + 2H2O + 3e- > MnO2 + 4OH-, =+0.59V
in alkaline: +7 > +6 > +4 (MnO4- > MnO42- >MnO2) (purple > green > dark brown)

+4; oxid agent, catalyst (2H2O2 >(MnO2)> 2H2O + O2)
MnO2 + 4H+ + 2e- > Mn2+ + 2H2O, =+1.23V
MnO2 + 4HCl >(heat)> MnCl2 + Cl2 + 2H2O, =-0.13V(since -ve > need heat )

+6; green
formation
  2MnO4- + MnO2 + 4OH- > 3MnO42- + 2H2O, =-0.60V
stable in alkaline
  MnO42- + 2H2O + 3e- > MnO2 + 4OH-, =+0.60V
conc alkaline; +6 more stable than +7
  4MnO4- + 4OH- > 4MnO42- + 2H2O + O2 [purple > green]
neutral & acid; +6 disproportionates > +7, +4
  3MnO42- + 2H2O > 2MnO4- + MnO2O + 4OH- , =+0.04V
[bubble CO2 to remove OH- > faster disproportionatn]
disproportionatn in acid
  3MnO42- + 4H+ > 2MnO4- + MnO2 + 2H2O , =+1.70V

+3; deep red
formation:
  4Mn2+ + MnO4- + 8H+ > Mn3+ + 4H2O, =+0.03V
disproportionatn: (+3 > +2, +4)
  2Mn3+ + 2H2O > Mn2+ + MnO2 + 4H+

+5; blue
stable in v.strong alkaline as MnO43-
disproportionatn: (+5 > +7, +4)
  3MnO43- + 4H+ > 2MnO4- + MnO2 + 2H2O

+2: most stable as half filled 3d orbitas (3d5)

Cobalt
+2: more stable than +3
[Co(H2O)6]3+(aq) + e- <> [Co(H2O)6]2+(aq), = +1.81V
+3: stabilised by ligands (strong complexing ligands: oxid of hydrated +2 > +3)

Co2+(aq) + 2OH-(aq) > Co(OH)2(s) (blue)
xs NH3(aq): Co(OH)2(s) > dissolve > pale brown sol, [Co(NH3)6]2+(aq)
  Co(OH)2(s) + 6NH3(aq) > [Co(NH3)6]2+(aq) + 2OH-(aq)

in air: [Co(NH3)6]2+(aq) oxidised > dark brown sol, [Co(NH3)6]3+(aq)
[Co(NH3)6]2+(aq) - e- > [Co(NH3)6]3+(aq), = -0.10V

[Co(NH3)6]3+: yellow orange
[Co(CN)6]3-: yellow
[Co(NH3)5Cl]2+: purple


  [CoCl4]2-(aq): tetrahedral, blue
  [Co(H2O)6]2+(aq): octahedral, pink
Co: in vitamin B12 as hexacoordinated Co(III) molecule
one ligand of molecule replaced by -CN > cyanocobalamin


Nickel
Extraction
nickel ore (Ni2S3) >(roast in air)> NiO >(reduce by C)>impure Ni
Ni2S3(s) + 4O2(g) > 2NiO(s) + 3SO2(g)
2NiO(s) + C(s) > 2Ni(s) + CO2(g)
Purification: (by Moud process)
(1)Ni(s) + 4CO(g) >(~50°C)> Ni(CO)4(g) [tetracarbonylnickel(0), volatile liq, tetrahedral molecule]
(2)Ni(CO)4(g) >(200°C)> Ni(s) + 4CO(g) [Ni: v.pure, 99.9%]
uses:
-catalyst (finely divided Ni produced by reducing NiO)
  -synthesis gas formation: C(s) + H2O(g) >(Ni, 1200°C)> CO(g) + H2(g) [CO, H2: synthesis gas]
  -margarine manufactre (vegetable oil + H2 >(Ni)> margarine)
-alloys (Ni- hard, high mp 1453°C, rel unreactive)
  nichrome: 80% Ni, Cr
  constantan: 40% Ni, Cu
  coinage Ag: 25% Ni, Cr
  stainless steel: 74% Fe, 18% Cr, 8% Ni
  AlNiCo (magnets)

IRON
Fe2+(s) pale green
Fe2+(aq) pale green [Fe(H2O)6]2+(aq)
Fe3+(s) pale violet (in alum, ammonium iron(III) sulphate)
Fe3+(aq) yellow-brown [Fe(H2O)6]3+(aq)
[Fe(CN)6]4-(aq) yellow
[Fe(CN)6]3-(aq) red

Fe2+ more stable in air:  Fe3+(aq) + e <> Fe2+(aq), = +0.77V

Effect of pH
acid medium: Fe2+(aq) more stable
Fe3+(aq) + e <> Fe2+(aq), = +0.77V
FeSO4(aq) acidified w/ H2SO4 to prevent air oxidation
alkaline medium: Fe3+(aq) more stable
Fe(OH)3(s) + e <> Fe(OH)2(s), = -0.56V

Effect of cyanide ligands
Fe3+ + CN- > [Fe(CN)6]3- complex more stable than free Fe3+(shown by reaction w/ I-)
[Fe(CN)6]3- + e <> [Fe(CN)6]4-, = +0.36V
½ I2 + e <> I-, = +0.54V
Fe3+(aq) + e <> Fe2+(aq), = +0.77V
Fe3+ can oxidise I- to I2 (+0.23V), [Fe(CN)6]3- can't(-0.18V)

Iron complexes
Fe2+ cpd (FeSO4) heat w/ KCN > white ppt of K2Fe''Fe''(CN)6 soluble in excess > [Fe(CN)6]4-
2Fe2+ + 6 KCN > K2Fe''Fe''(CN)6 + 4K+
Fe2+ + 6CN- > [Fe(CN)6]4- (yellow sol)

hexacyanoferrate(II) complex + oxid agent (Cl gas) > hexacyanoferrate(III) complex
[Fe(CN)6]4- + Cl2 > 2[Fe(CN)6]3- + 2Cl-

hexacyanoferrate(III) complex, [Fe(CN)6]3- more stable than hexacyanoferrate(II) complex, [Fe(CN)6]4-

[Fe(CN)6]3-(aq): red- used to test for Fe2+ > deep blue complex
Fe2+ + [Fe(CN)6]3- > Fe[Fe(CN)6]- (deep blue)
potassium thiocyanate, KSCN: test for Fe3+ > blood red complex
[Fe(H2O)6]3+(aq) + KSCN > [Fe(SCN)(H2O)5]2+(aq) + H2O

Fe(CO)5: pentacarbonyl iron(0), trigonal bipyramidal molecule

Rusting
conditions: presence of water & oxygen(air)
oxidized/ anodic area: Fe(s) > Fe2+(aq) + 2e
reduced/ cathodic area: 2H2O + O2(aq)+ 4e > 4OH-(aq)
Formation of rust:
    Fe2+ + 2OH- > Fe(OH)2(s)
    2Fe(OH)2(s) + ½O2 + xH2O <> Fe2O3.xH2O(s) + 2H2O
    [Fe2O3.xH2O(s): reddish brown rust]
Preventing rusting
(1)coating: prevent O2 & H2O from coming into contact w/ Fe
-painting- contain phosphoric acid, insoluble layer of iron(III) phosphate
-galvanizing- coat w/ more reactive metal > protects when scratch iron surface since metal more electropositive (sacrificial corrosion)
(2)alloying: Cr in stainless steel > corrosion resistant (non-porous surface oxide film)
(3)cathodic protection: more reactive metal(Zn, Mg) dissolves instead of iron [anodic process: sacrificial corrosion]
(4)inhibition: prevents cathodic & anodic processes
HCO3-(aq): remove OH- from cathode > insoluble carbonate forms preventing oxygen reaching surface
  HCO3- + OH- > CO32- + H2O

Catalytic properties
Homogeneous catalyst
-as Fe2+ / Fe3+ in oxidation of iodide ions by peroxodisulphate, S2O82-
S2O82- + 2I- > 2SO42- + I2
-due to lower activation energy [also that S2O82- & I- are anions > repel, Fe2+ & S2O82-, Fe3+ & I-, opposite charge > attract > faster reaction]

½S2O82- + 2e <> SO42-, = +2.01
I2 + 2e<> 2I-, = +0.54
Fe3+ + e <> Fe2+, = +0.77V

(1) Fe3+ + 2I- <> Fe2+ + I2
(2) Fe2+ + S2O82- <> Fe3+ + 2SO42-
        S2O82- + 2I- >( Fe2+/Fe3+)> 2SO42- + I2
Heterogeneous catalyst
-as Fe / Fe2O3 in Haber process [available 3d, 4s electrons > weak bonds w/ reactant molecules > surface adsorption > weaken bond in reactant molecules > lower activation energy & increase surface area]

Biological importance
Fe2+(aq) from liver used to catalyse respiratory reaction in cytohrome chain (Fe2+ > Fe3+ > Fe2+)
iron(II): component of haemoglobin used to transport oxygen to body

Fe <- H2O, Fe <- O2, Fe <- CO2: weak dative bonds > reversible
Fe <- CO, Fe <- CN: strong dative bonds [CO,CN: strong ligands] > irreversible

COPPER
[Cu(H2O)6]2+ blue
[CuCl4]- yellow brown
[Cu(NH3)4(H2O)2]2+ deep blue
[Cu(EDTA)]2- light blue

+1: white [due to filled 3d orbital]
+2: blue/green [blue-green in solid, blue in sol: blue due to [Cu(H2O)6]2+(aq)]
+1: stable in solid or complex form, +2: stable in solid / aq form

Cu+(aq) > disproportionates to Cu(s) + Cu2+(aq)
2Cu+(aq) > Cu(s) + Cu2+(aq), ΔH = -404kJ/mol, = +0.37
exothermic > Cu+ thermodynamically unstable rel to Cu & Cu2+
+ve elec pot > feasible under std conditions
KC = 106 mol-1dm3 => equiblm far on right

orange red copper(I) oxide + sulphuric acid > blue copper(II) sulphate(aq) + red brown copper metal
Cu2O(s) + H2SO4 > CuSO4 + Cu(s) + H2O
CuO(s) + H2SO4 > CuSO4 + H2O [copper(II) ion > just neutralisation]

copper(I) & copper(II) cpds & complexes
CuI: copper(II) ions added to iodide > white ppt of CuI in brown sol, I2
2Cu2+ + 4I- > 2CuI + I2
thiosulphate ions used to remove brown I2 > obtain white ppt of CuI, soluble in excess > colourless sol
[CuCl2]-: dichlorocuprate(I) ions, formed when CuI + hydrochloric acid
CuI + 2HCl > [CuCl2]- + 2H+ + I-

stability: [Cu(H2O)6]2+ < [CuCl4]- < [Cu(NH3)4(H2O)2]2+ < [Cu(EDTA)]2-
due to stronger ligands

[Cu(H2O)6]2+ + 4Cl- <> [CuCl4(H2O)2]2+ + 2H2O
blue > green > yellow [CuCl4(H2O)2]2+ (more stable: Cl- ligands slowly displace water ligands one by one)

[Cu(H2O)6]2+ + Cl- <> [CuCl(H2O)5]+
[CuCl(H2O)5]+ + Cl- <> [CuCl2(H2O)4] + H2O
[CuCl2(H2O)4] + Cl- <> [CuCl3(H2O)3]- + H2O
[CuCl3(H2O)3]- + Cl- <> [CuCl4(H2O)2]2- + H2O

[Cu(H2O)6]2+ > [CuCl(H2O)5]+ > [CuCl2(H2O)4] > [CuCl3(H2O)3]- > [CuCl4(H2O)2]2-
blue > bluish green > green > greenish yellow > yellow

[Cu(H2O)6]2+: blue
[CuCl(H2O)5]+: bluish green
[CuCl2(H2O)4]: green
[CuCl3(H2O)3]-: greenish yellow
[CuCl4(H2O)2]2-: yellow

dilution reverses process; yellow > green > blue

[Cu(NH3)4(H2O)2]2+ + EDTA4- <> [Cu(EDTA)]2- + 2H2O + 4NH3
deep blue > light blue [edta4-: stronger ligands > displace NH3 & water ligands]
[Cu(EDTA)]2-:


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