23 Tranistion Metals Flashcards
Definition of transition metal element
The formal definition of a transition element is that it is one that forms at least one stable ion with a path full d-shell of electrons. Scandium only forms Sc3+ (3d0) and zinc only forms Zn2+ (3d10). ( they are d block elements but not transition metals)
Chemical properties of transition metals
Variable oxidation states - have more than one oxidation state
Colour - different coloured ions
Catalysis - affects the rate of reaction without being used up
Complex formation - transition elements form complex ions
Co-ordination number
The number of ligand molecules bonded to a metal ion
Ligand
An atom, ion or molecule that forms a co-ordinate (dative) bond with a transition metal ion using a lone pair of electrons
Example of ligands
H2O:
:NH3
:Cl-
:CN-
Aqua ions
If you dissolve the salt of a transition metal in water
Copper sulphate = the positive charged metal ions becomes surrounded by water molecules acting as ligands
Multidentate ligands
More than one atom with a lone pair of electrons which can bond to a transition metal ion
Bidentate ligands
Ethane 1,2 diamine
Ethanedioate (oxalate) ion
Benzene -1,2- diol
Chelate effect
Add a hexadentate ligand such as EDTA to a solution of a transition metal salt
[Cu(H2O)6]2+ + EDTA4- —— [CuEDTA]2- +6H2O
Haemoglobin
Red pigment in blood
Responsible for carrying oxygen from the lungs to the cells of the body
Fe2+
Tranistion metals
Electrons are being added to the d-sub-level
Good conductor of heat and electricity
Hard , strong ,high melting and boiling point
Low chemical reactivity
co-ordination number
number of co-ordinate bonds to ligands that surround the d-block metal ion
Aquas ions
dissolve the salt of a transition metal in water, the positively charged metal ion becomes surrounded by water molecules acting as ligands
Ethane-1,2-diamine
each nitrogen had a lone pair which can forms a co-ordinate bond to the metal ion
EDTA
this can act as a hexadentate ligand using Loeb pairs on four oxygen and both nitrogen atoms. complex ions with polydentate ligands are called chelates. Chelates can be used to effectively removed d-block metal ions from solution
chelate effect
enhanced affinity of chelating ligands for a metal ion compared to the affinity of a collection of similar nonchelating ligands for the same metal.
Haemoglobin
red pigment
carries oxygen form the lungs
four of the co-ordination sites are taken up by a ring system called a porphyrin which acts as a tetra dentate ligand.
anaemia
shortage of haemoglobin
body suffers from a lack of oxygen
metal compounds are coloured
coloured is caused by the compounds absorbing energy that corresponds to light in the visible region of the spectrum.
why are transition metal complexes coloured
transition metal compounds are coloured because they have part filled d-orbitals
electrons can move between d-orbitals
E = hv = hc/λ
frequency of light is related to the energy difference
frequency is related to the colour of light. violent is of high energy and therefore high frequency and red is low energy and low frequency
colour of transition metal complex depends on the energy gap which depends on the oxidation number and also on the ligands.
Colorimetry
a simple colorimeter uses a light source and a sector to measure the amount of light of a particular wavelength that passes through a coloured solution. the more concentrated the solution, the less light transmitted through the solution. a colorimeter is used with a suitable calibration graph to measure the concentration of solutions of coloured transition metal compounds.
redox titrations
find out how much acid is required to react with certain volume of base
Fe2+ reacts with potassium manganate int he ratio 5:1
using a burette, you gradually add potassium manganate solution to solution containing Fe2+ ions acidified with excess dilute sulphuric acid. the purple colour disappers as the MnO4- ions are converted to pale pink Mn2+ ions to leave a virtually colourless solution.
oxidation of transition metal ions in alkaline solutions
high oxidation state of a mental are reduced in acidic solution. oxidation of lower oxidation states of transition metal ions tends to happen in alkaline solution
catalyst
affect the rate of reaction without being chemically changed themselves
heterogenous catalyst
heterogenous catalysts are present in a reaction in a difference phase than the reactants.
catalytic action occurs on the solid surface
reactants pass over the catalyst surface, which remains in place so the catalyst is not lost and does not need to be separated from the products.
(A heterogeneous catalyst is in a different phase from the reactants and the reaction occurs at active sites on the surface)
making heterogenous catalyst more efficient
increase their surface area
spread the catalyst onto an inert support medium. this increases the surface-to-mass ratio, so a little goes a long way.
catalysts don’t fast forever
overtime surfaces become covered with unwanted impurities. ( poisoning).
catalyst converters become poisoned by substances used in fuel additive
finely divided catalyst may gradually be lost from the support medium
Haber process
iron catalyst
last around 5 years before it become poisoned by impurities in the gas stream
contact process
produces sulphuric acid
2SO2 + O2 <====> 2SO3
SO2 + V2O5 —-> SO3 + V2O4
2V2O4 + O2 —-> 2V2O5
vanadium oxide is regenerated unchanged. each of the two steps has a lower activation energy than the uncatalysed single step
manufacture of methanol
synthesis gas is made from methane
CH4(g) + H2O(g) —> CO + 3H2(g)
CO + 2H2(g) —> CH3OH(g)
reaction is catalysed by chromium oxide
homogeneous catalyst
when the catalyst is in the same phase as the reactant, an intermediate species is formed.
autocatalysis
when one of the products of the reaction is the catalyst. so the reaction starts slow and as the concatenation increase the rate of reaction
oxidation of ethanediol acid by manganate ions
example of an auto catalysed reaction
titration
2MnO4-(aq) + 16H+ 5C2O42-(aq) —–> 2Mn2+(aq) + 8H2O(l) + 10CO2(g)
4Mn2+(aq) + MnO4- (aq) + 8H+(aq) —> 5Mn3+(aq) + 4H2O(l)
2Mn3+(aq) + C2O42-(aq) –> 2CO2(g) + MN2+(aq)
reaction is followed using a colorimeter to measure the concentration of MnO4- which is purple
complex
central metal atom or ion surrounded by ligands.
monodentate
H2O, NH3 and Cl−
what two ligands are similar in size?
NH3 and H2O
Haem
In haemoglobin
Haem is an iron(II) complex with a multidentate ligand.
carbon monoxide and haemoglobin
Oxygen forms a co-ordinate bond to Fe(II) in haemoglobin, enabling oxygen to be transported in the blood.
Carbon monoxide is toxic because it replaces oxygen co-ordinately bonded to Fe(II) in haemoglobin.
Tollens’ reagent
Ag+ forms the linear complex [Ag(NH3)2]+ as used in Tollens’ reagent
Vanadium and oxidation states
Vanadium species in oxidation states IV, III and II are formed by the reduction of vanadate(V) ions by zinc in acidic solution.
