Coloured ions Flashcards
(28 cards)
colour of transition metal compound depends on…
oxidation state
type of ligand
coordination number
how do transition metal compounds show colour
absorbs frequencies of light
d electrons are promoted to high levels from ground state to excited state
colour observed is the light not absorbed and is transmitted
ΔE equation
ΔE = hv
ΔE is the energy difference between split d orbitals
h is Phlanck’s constant (6.63 x 10-34Js)
v is the frequency of absorbed radiation (Hz)
v = speed of light/ wavelength
adding ligand to complex ions equations and colours (2)
[Fe(H2O)6]2+(aq) + 3bipy(aq) -> [Fe(bipy)3]2+(aq) + 6H2O(l)
pale green -> intense red
[Fe(H2O)6]3+(aq) + NCS-(aq) -> [Fe(H2O)5NCS]2+(aq) + H2O(l)
pale violet -> intense blood red
why do Cu+ and Zn2+ appear colourless
have a full d orbital (no space for electrons to transfer) so appear colourless
reduction of vanadate ions
ammonium vanadate(V) NH4VO3 reduced by zinc in acidic solution VO3^- +5 white Addition of acid VO2^+ +5 yellow Addition of zinc reducing agent VO^2+ +4 blue V^3+ +3 green V^2+ +2 violet
Fe2+ oxidised to Fe3+ by ClO3- ions in acidic conditions
Fe2+ -> Fe3+ + e-
6e- + 6H+ + ClO3- -> Cl- + 3H2O
6Fe2+ + 6H+ + ClO3- -> 6Fe3+ + Cl- + 3H2O
Fe2+ oxidised to Fe3+ by Cr2O72- ions in acidic conditions
Fe2+ -> Fe3+ + e-
6e- + 14H+ + Cr2O72- -> 2Cr3+ + 7H2O
6Fe2+ + 14H+ + Cr2O72- -> 2Cr3+ + 6Fe3+ + 7H2O
Fe2+ oxidised to Fe3+ by MnO4- ions oxidising agent in acidic conditions
Fe2+ -> Fe3+ + e-
5e- + 8H+ + MnO4- -> Mn2+ + 4H2O (purple to pale pink/ colourless)
5Fe2+ + 8H+ + MnO4- -> 5Fe3+ + Mn2+ + 4H2O
must be dilute H2SO4 for redox titrations
strong acid for high concentration H+ (so not weak ethanoic acid )
Cannot be c. H2SO4 or HNO3 oxidising agent as it will oxidise Fe2+ and titre ↓
Cannot be HCl reducing agent as Cl- oxidised to toxic Cl2 by MnO4- and titre ↑
manganate titration with hydrogen peroxide
H2O2 -> O2 + 2H+ + 2e-
5e- + 8H+ + MnO4- -> Mn2+ + 4H2O
6H+ + 2MnO4- + 5H2O2 -> 2Mn2+ + 8H2O + 5O2
manganate titration with ethanedioate
slow reaction as two negative ions repel so heated to 60°C (autocatalysed)
C2O42- -> 2CO2 + 2e-
5e- + 8H+ + MnO4- -> Mn2+ + 4H2O
16H+ + 2MnO4- + 5C2O42- -> 2Mn2+ + 8H2O + 10CO2
alternative catalysed route:
4Mn2+ + MnO4- + 8H+ -> 5Mn3+ + 4H2O
2Mn3+ + C2O42- -> 2Mn2+ + 2CO2
colour [Al(H2O)6]3+
colourless solution
[Al(H2O)6]3+ and OH- or NH3
deprotonation acid base reaction
[Al(H2O)6]3+(aq) + 3OH-(aq) -> Al(H2O)3(OH)3 (s) + 3H2O(l)
[Al(H2O)6]3+(aq) + 3NH3 (aq) -> Al(H2O)3(OH)3 (s) + 3NH4+(aq)
White precipitate (amphoteric)
Can react with excess OH-
Al(H2O)3(OH)3 (s) + OH-(aq) -> [Al(OH)4]-(aq) + 3H2O(l)
Colourless solution
[Al(H2O)6]3+ and CO32-
acidity reaction
2[Al(H2O)6]3+(aq) + 3CO32-(aq) -> 2Al(H2O)3(OH)3 (s) + 3CO2 (g) + 3H2O(l)
White precipitate (amphoteric) and bubbles
[Al(H2O)6]3+ and c.Cl-
[Al(H2O)6]3+(aq) + 4Cl-(aq) -> [AlCl4]-(aq) + 6H2O(l)
Colourless solution
colour [Fe(H2O)6]3+
yellow solution
[Fe(H2O)6]3+ and OH- or NH3
deprotonation acid base reaction
[Fe(H2O)6]3+(aq) + 3OH-(aq) -> Fe(H2O)3(OH)3 (s) + 3H2O(l)
[Fe(H2O)6]3+(aq) + 3NH3 (aq) -> Fe(H2O)3(OH)3 (s) + 3NH4+(aq)
Red/ brown precipitate (rust)
[Fe(H2O)6]3+ and CO32-
acidity reaction
2[Fe(H2O)6]3+(aq) + 3CO32-(aq) -> 2Fe(H2O)3(OH)3 (s) + 3CO2 (g) + 3H2O(l)
Red/ brown precipitate (rust)
[Fe(H2O)6]3+ and c.Cl-
[Fe(H2O)6]3+(aq) + 4Cl-(aq) -> [FeCl4]-(aq) + 6H2O(l)
Yellow solution
colour [Fe(H2O)6]2+
green solution
[Fe(H2O)6]2+ and OH- or NH3
deprotonation acid base reaction
[Fe(H2O)6]2+(aq) + 2OH-(aq) -> Fe(H2O)4(OH)2 (s) + 2H2O(l)
[Fe(H2O)6]2+(aq) + 2NH3 (aq) -> Fe(H2O)4(OH)2 (s) + 2NH4+(aq)
Green precipitate
Can react with air or H2O2 (oxidation)
Fe(H2O)3(OH)3 (s) red/ brown precipitate
[Fe(H2O)6]2+ and CO32-
precipitation reaction
[Fe(H2O)6]3+(aq) + CO32-(aq) -> FeCO3 + 6H2O(l)
Green precipitate
[Fe(H2O)6]2+ and c.Cl-
[Fe(H2O)6]3+(aq) + 4Cl-(aq) -> [FeCl4]2-(aq) + 6H2O(l)
Yellow solution
