Transition Metals Flashcards
Ratio of Fe2+ to MnO4 - in redox titration of acidified potassium manganate (VII)
5:1
Ratio of C2O4 2- to MnO4 - in analysis of C2O4 2-
2 and 1/2 : 1
What is autocatalysis and what is an example
A reaction where one of the products acts as a catalyst
Mn2+
Ionic equations for analysis of Fe2+
Fe2+ = Fe3+ + e-
S2O8 2- + 2e- = 2SO4 2-
2Fe 2+ + S2O8 = 2Fe 3+ +2SO42-
Fe3+ + e- = Fe2+
2I- = I2 + 2e-
2Fe2+ + 2I- = 2Fe2+ + I2
Cyclic
Initially reactants are both negative and repel
Purple- is decolourised
Contact process equations
V2O5 + SO2 = V2O4 + SO3
V2O4 + 1/2 O2 = V2O5
Overall: V2O4 + 1/2 O2 = V2O5
Iodine and peroxodisulfate reactions (half and full equations)
2I- + S2O8 2- = I2 +2SO4 2-
S2O8 2- + 2e- = 2SO4 2-
Fe 3+ + e- = Fe2+
I2 + 2e- = 2I-
Reaction between manganate (VII)
Ions and ethanedioate ions
Half equations
5Mn 2+ = 5Mn 3+ + 5e-
MnO4 - +8H+ +5e- = Mn2+ +4H2O
4Mn2+ +MnO4 - +8H+ = 5Mn3+ + 4H2O
5Mn+ + 5e- = 5Mn2+
C2O4 2- = 2CO2 + 2e-
2Mn2+ + C2O4 2- = 2Mn 2+ + 2CO2
What colour is Ti 2+
violet
what colour is Ti 3+
purple
What colour is V 2+
Violet
What colour is V 3+
green
what colour is VO 2+
blue
what colour is VO2 +
yellow
what colour is Cr 3+
green
what colour is Cr2O7 2-
orange
what colour is Mn 2+
pale pink/ colourless
what colour is MnO4 2-
green
what colour is MnO4 -
purple
what colour is Fe 2+
pale green
what colour is Fe 3+
yellow/ purple
what colour is Co 2+
pink
what colour is Ni 2+
green
what colour is Cu 2+
pale blue
what are the chemical properties of transition metals?
Form complex ions
Form coloured ions
Good catalysts
Exist in variable oxidation states
Define what is meant by a heterogeneous catalyst
a catalyst in a different phase or state from the reactants
In what circumstance does colorimetry sometimes not help distinguish transition metal ions
when their electron configuration is no longer that of a transition metal i.e. they have a full d orbital
A full shell means there is no position for electrons from lower sub-shells to move up to and therefore it is colourless.
give the equation which relates energy change to the Planck constant (h) and the frequency of visible light (v)
change in energy = hv
explain why electron transition causes a solution containing a transition metal ion to be coloured
One colour of visible light is absorbed
remaining frequencies are reflected or transmitted
state 3 features of transition metal complexes that cause a change in the energy change value between ground and excited state (and so their colour)
oxidation state
ligand
metal involved
coordination number
define a ligand
a particle with a lone pair which bonds to a metal by a coordinate bond
define a complex
metal ion with coordinately bonded ligands
define coordination number
number of coordinate bonds from a ligand to the metal ion
define a lewis base
lone pair donor
define a lewis acid
lone pair acceptor
what does colorimetry measure
concentration of a solution- the more concentrated the solution, the more visible light it absorbs
what are the common oxidation states of Manganese (Mn)
+2 +4 +6 +7
what are the common oxidation states of iron (Fe)
+2 +3 +6
what are the common oxidation states of copper (Cu)
+1 +2
how to change the oxidation state of a transition metal with pH
oxidise in alkaline conditions
reduce in acidic conditions
how do heterogeneous catalysts work
A reactant is ADSORBED onto the surface at the catalysts active site
The contact weakens bonds in the reactant
The reactants react with one another
The product is DE-ADSORBED
What is a homogeneous catalyst
a catalyst in the same phase or state as the reactants
often reactions take place in solution
reaction creates an intermediate species formed from reactants and the catalyst which then reacts further to regenerate the catalyst
How do coloured ions occur?
Electrons move between sub shells
The gap between the shells corresponds to the energy of visible light
Electrons absorb visible light in order to move up a level
The colour you see are the colours which are emitted/reflected NOT absorbed
This doesn’t occur with ions that have and empty or full d sub shell
Factors that affect the colour of a transition metal ion
Identity of metal
Oxidation state of metal
Identity of ligand
Coordination number
How does ultraviolet/ visible spectroscopy work
The frequency of a complex absorbs visible light which can be measured with spectroscopy
Light passes through the complex and the frequencies passing through are detected, those that do not pass through are absorbed
The more concentrated the solution the more light absorbed
What is the coordination number for CN when it acts as a ligand
1
What is the coordination number of ammonia when it acts as a ligand
1
What is the coordination number when 1,2 diaminothane acts as a ligand (NH2-CH2-CH2-NH3)
2
What is the coordination number for C2O4 when it acts like a ligand
2
What is the coordination of EDTA when it acts as a ligand
6
What is catalyst poisoning ?
When a substance adsorbs to the catalyst active site so strongly that that are not released thus blocking the active site from further catalysing the reaction
Formula for 1,2 diaminoethane
H2N-CH2-CH2-NH2
