Transition metals Flashcards
what is meant by a transition metal
A transition metal is a d-block element that can form at least one stable ion with an incomplete d sub-shell
What are the 4 characteristics of transition metals
- complex formation
- formation of coloured ions
- variable oxidation state
- catalyts
What colour complex is vanadium 2+ in solution
violet
What colour is vanadium 3+ in solution
green
What colour complex does vO 2+
blue
What colour does VO2 + form
Yellow
What are the trends in oxidation states
- Relative stability of +2 state with respect to +3 state increases across the period
- Compounds with high oxidation states tend to be oxidising agents e.g MnO4 -
- Compounds with low oxidation states are often reducing agents e.g V2+ & Fe2+
What metal can reduce transition metals from a higher oxidation state to a lower oxidation state
Zinc
What colour does chromium three plus make
green/violet
What colour is Cr2O72-
orange
What colour is Mn 2+
Pink
What colour is MNO4 2-
Purple
Why are scandium and zinc not transition metals
they have a full d outer sub shell
What colour is Fe2+
Pale green
What colour does Fe 3+ form
Yellow
What colour is Co 2+
Pink
What colour is Cu 2+
Blue
State what is meant by a complex metal
:is a central metal ion surrounded by ligand linked by coordinate bonds
State what is meant by a ligand
An atom, ion or molecule which can donate a lone pair of electrons
State what is meant by co-ordination number
the number of co-ordinate bonds in a complex
What is a monodentate ligand and give examples of one
a ligand that can form one co-ordinate bond per ligand
Examples are water, ammonia, cl-
What is a bidentate ligand and examples
two atoms with lone pairs and can form two coordinate bonds per ligand
examples are: Ethabedioate, ethane-1-2, diamine
What is a multidentate ligand and give examples
which can form six coordinate bonds per ligand
examples is EDTA
What determines the shape of a complex
size of ligands
co-ordination number
What shape do complexes with a co-ordination number of 6 form
octahedral shape
What kind of isomerism do complexes show
Cis and trans
Some octahedral complexes can form optical isomers
what types of ligands do these complexes have
3 bidentate ligands can form two optical isomers
What shape do complexes with a coordination number of 4 form
Tetrahedral or square planar
example of tetrahedral is cucl4
the only square planar one you have to know is CisPlatin
What shape do complexes with a coordination number of 2 form
Linear
example is tollens reagent
What happens when
[Co(H2O)6]2+ reacts with 6 ammonia molecules
Forms
[Co(H2O)6]2+ (aq) + 6NH3 (aq) →[Co(NH3 )6]2+ (aq) + 6H2O (l)
Pink to yellow
The ligands NH3 and H2O are similar in size and are uncharged, so exchange occurs without change of co-ordination number
what happens when [Cu(H2O)6]2+ reacts with ammonia
There is a partial substitution
[Cu(H2O)6]2+ (aq) + 4NH3 (aq) [Cu(NH3 )4 (H2O)2]2+ (aq) + 4H2O (l)
colour change: blue to deep blue
Reacts with excess ammonia
What happens when [Cu(H2O)6]2+ reacts with chloride
[Cu(H2O)6]2+ + 4Cl → [CuCl4]2- + 6H2O
The Colour change is blue to green/yellow
co-ordination number changes from 6 to 4 because Cl- is a bigger ligand
What happens when [Co(H2O)6]2+ reacts with chloride
[Co(H2O)6]2+ + 4Cl → [CoCl4]2- + 6H2O
The Colour change is pink to blue
co-ordination number changes from 6 to 4 because Cl- is a bigger ligand
What happens when [Fe(H2O)6]3+ reacts with 4 chloride ions
[Fe(H2O)6]3+ + 4Cl → [FeCl4]- + 6H2O
The Colour change is yellow to yellow
co-ordination number changes from 6 to 4 because Cl- is a bigger ligand
Why can’t the reaction between [Fe(H20)6]3+ and cyanide ions not be easily reversed
because the cyanide ligand forms a stronger bond to the iron
How does human haemoglobin transport oxygen
- oxygen substitutes the water ligand in the lungs
- this forms oxyhaemglobin, this the deposit water at oxygen and picks up water instead
What is the effect of carbon monoxide on haemoglobin
- Carbon monoxide is inhaled carbon monoxide replaces the water ligand
- carbon monoxide bonds strongly to haemoglobin
- thsi means oxygen won’t be picked up
What is the chelate effect
When a monodentate lighand is substituted of with a bidentate or a multidentate ligand leads to a more stable complex
What happens to orbitals when a ligand is added to it
they go through d-orbital splitting, where two orbitals are in a higher energy level and three are in a lower energy level
Explain why complexes with a partially filled d subshell can form coloured complexes
-The electrons can now move to a higher energy level (from ground state to the excited state because they have been exited,
due to absorbing visible light
the light that is not absorbed is transmitted to give the substance colour
ΔE = hv or ΔE = hc/λ
above is the equation for delta E (energy gap) what does each symbol mean
v = frequency of light absorbed (unit s-1 or Hz)
H = Planck’s constant 6.63 × 10–34 (J s)
E = energy difference between split orbitals (J)
c = speed of light 3.00 x 108 (m s–1 )
λ = wavelength of light absorbed (m)
What is delta E and is the size of delta e dependent on
energy gap
- Dependent on the central atom and oxidation tate
- type of ligand
- co-ordination number
Why do some complexes produce colourless or white
because those complexes gave full or empty three-d sub shell, so no electrons can migrate to a higher energy level
What can affect the redox potential of transition metals
if they are not done in standard conditions
The more acidic the solution the more …… the electrode potential
larger the electrode potential which means it easily reduced
What are the two types of catalyst
Heterogenous and homogenous
What happens to vandium 5+ in acidic solution if you add zinc
will reduce the vanadium down through each successive oxidation state,
and the colour would change from yellow to blue to green to violet.
State what is meant by a heterogenous catalyst
heterogeneous catalyst is in a different phase from the reactants
State what is meant by a homogenous catalyst
homogeneous catalyst is in the same phase as the reactants
How do heterogeneous catalysts work
- Reactants adsorb into the surface (in mark schemes) by forming bonds with atoms at active sites on the catalyst’s surface
- bonds in the reactants are weakened and break or a reaction happens
- the product desorbs of the surface of the catalyst
How is vanadium used in the contact process, give the overall and step equations
Overall equation : 2SO2 + O2 → 2SO3
step 1 SO2 + V2O5→ SO3 + V2O4
step 2: 2V2O4 + ½ O2 → 2V2O5
What is the name of the catalyst used in the Haber process
Iron
What is meant by the phrase poising catalysts?
when poisoned by impurities and which reduces efficiency
this means that less product is made, catalyst needs to be replaced or cleaned,
How do homogenous catalysts work
-form an intermediate
What’s different about homogenous energy profiles
they have two activation energies
How do homogenous catalysts work with S2o8 and I-
s2o8 2- + 2Fe2+ → 2Fe3+ + 2so4 2-
2fe3+ + 2I- → I2 + 2Fe2+
Fe2+ is refomed
What is autocatalysis
another form of homogenous catalysts where the product catalyses the reaction
What is an example of autocatalysis
Mn2+
2MnO4- + 16h+ + 5C2O42- → 2Mn2+ + 8H20 + 10Co2
then
Mn2+ + Mno4- + 8H+ → 2Mn3+ + 4H2o
then
2Mn3+ c2O42- + 2Mn 2+ + 2Co2
