2.5- Transition metals Flashcards
What are the four characteristics of transition metals
.Complex formation
.Formation of coloured ions
.Variable oxidation states
. Catalytic acitivity
Why is zinc no a transtion metal
Zn can only form a +2 ions, it has a complete d orital and so does not meet the criteria of having an incomplete d orbital
What causes the transition metal characteristics
An incomplete d orbital
What is a complex and a ligand
A complex is a central metal ion that is surrounded by ligands
A ligand is an atom, ion or molecule which can donate a lone electron pair
Give the definition of co ordinate bonding
Co ordinate bonding is when the shared pair of electrons in the covalent bond come from only one of the bonding atoms
What is the co ordination number
The number of co ordinate bonds formed to a central metal ions
What are the difference between mono, bi and multi dentate ligands
Ligands can be monodentate that form one co ordinate bond per ligand, or bidentate which can form to co ordinate bonds per ligand or multidentate that form 6 co ordinate bonds per ligand
Give examples of all 3 of these different ligand types
Monodentate- H2O, NH3 and Cl-
Bidentate- NH2CH2CH2NH2
Multidentate - EDTA4-
When you add high concentraiton of chloride ions to an aqueous ions what occurs
. A subsitution reaction occurs and the co ordination number will change from 6 to 4, the 6 H20 are substituted for the Cl-
What occurs when you add bidentate ligands to aqueous ions
The H20 will get substitued for the bidentate ligand, the ligand will be able to form 2 co ordinate bonds per ligand
What occurs when you add a dilute aquesous solutions containing ethandioate ions to a solution containing aqueous copper ions
.Partial substitution will occur
. 4 H20 ligands will be substituted off for 2 of the C204 2- ions
What is a multidentate ligand, and give and example
Mutlidentate ligands can form more than 2 co ordinate bonds per ligand, EDTA 4- is a multidentate ligand and can form 6 co ordinate bonds per ligand
It has 6 donor sites, at 4Os and 2Ns
How does oxygen get transported in the blood
Oxygen forms a co ordinate bond to Fe in haemoglobin enabling oxygen to be transported in the blood
Why is CO toxic to humans
CO is toxic to humans becuase CO can form a strong co ordinate bond with haemoglobin, this is a stronger bond that that made with oxygen and so it replaces the oxygen attaching to the haemoglobin.
Why does subsitiution of a monodentate ligand for a bidentate or multidentate ligand give a more stable complex
. This is due to the chelate effect
. There is an increase of entropy because there are more moles of products that the reactants
. The enthalpy change is small as there are similar numbers of bonds in both complexes
. G will be negative as S is positive and H is small
Why is EDTA 4- added to rivers and used in shampoos
. Becuse EDTA complexes are very stable, they can be added to rivers to remove the poisonous heavy metal ions as the EDTA complexes are not toxis
.They can be used in shampoos to remove the Calcium ions that are present in water to help lathering
What are the different shapes of complex ions
.Octahedral- H2O and NH3
.Tetrahedral- Cl-
.Square planar - Cl and NH3
.Linear- NH3
What is the isomerism shown in square planar, and give an example
. There is cis-trans isomerism in square planar complexes
. An example is cis platin, NH3 and Cl
Give examples of both the types of isomerisms with octahedral complexes
.There is cis and trans isomerism, for example with a complex that has 6 ligand with 2 of them that are different to the others
. There is also optical isomerism aswell, these occur with bidentate ligands that are attached to a complex ion
What causes colour changes in coloured ions
. Oxidation state
. Co ordination number
.Ligand
How does colour change arise
Colour arises from electronic transitions from the ground state to excited states between the different d orbitals
A portion of visible light is absorbed to promote d electrons to higher energy levels, the light that is not absorbed is transmitted to give the substance colour
What are the 2 equations for E
E= hv
E= hc/lamda
v= Frequency of light absorbed in s-1/Hz
h= Plancks constant
E = energy difference between split orbitals
c = speed of light in ms-1
lamda = wavelength of light absorbed in m
Give examples of compounds without the colours
Scandium is a member of the d block, but its ion hasnt got any electrons in the d orbital to move around so there is not an energy transfer equal to that of visible light
Also in the case of the Zn 2+ ions and the Cu+ ions the d shell is full so ther is no space for the electrons to transfer
What is the method for spectophotometry
.Add an appropriate ligand to intensify the colour
. Make up solutions of known concentration
. Measure the absorption or transmission
. Plot graph of absorption vs concentration
.Measure absorption of unknown and compare
Why would you add an appropriate ligand when measuring absorption
Some complexes only have pale colours and do not absorb light strongly, in these cases a suitable ligand is added to intensify the colour
Why do spectrophotomers have a coloured filter
They are used to allow the wavelengths of light through that would be most strongly absorbed by the coloured solution
What happens when visible light of increasing frequency is passed to a sample of a coloured complex ion
Some of the light is absorbed, and the amount that is absorbed is proportional to the concentration of the absorbing species, and the distance travelled through the solution
What are all of the different oxidation states of vanadium
VO2+ - 5 oxidation state- Yellow
VO^2+- 4 oxidation state - Blue
V3+- 3 oxidation state- Green
V2+- 2 oxidation state- Violet
How do you reduce vanadium
Addition of zinc in an acidic solution
How does the vanadium ion with a +5 oxidation state usually exist
. Solid compound in the from of VO3-
. Addition of acid to the solid will turn into the yellow solution containing the VO2+ ion
What is the colour change in a manganate titration where the maganate is in the burette
Colourless to purple
Which acid is suitable for manganate titrations and why
.Dilute sulfuric acid is used
.Insufficient volumes will mean that the solution is not acidic enough and MnO2 will be produced instead of Mn2+
. This is a brown colour and will mask the colour change and lead to an inaccurate volume of manganate being used in the titration
. Using a weak acid like ethanoic will have the same effect as it does not supply the large amount of hydrogen ions that are needed
.It cannot be conc HCL and the Cl- ions will be oxidised to Cl2 by the MnO4- due to the electrode potential
.It cannot be nitric acid as it is an oxidising agent and will oxidise the Fe ions due to electrode potential
What is the definition of a catalyst
Catalysts increase reaction rates without getting used up, they do this by providing an alternative route will a lower activation energy
What is the difference between a hetro and homogenous catalyst
. Heterogeneous catalyst are in a different phase from the reactants
.Homogenous catalyst are in the same phase as the reactants
Explain how a catalyst increases the rate of reaction
.Adsorption of reactants at active sites on the surface may lead to catalytic action
. Active site is where the reactants adsorb on to the surface of the catalyst
. This results in the bonds weakening within the reactant molecules
. Higher conc of reactant at the solid surface leading to a higher frequency
How does the strength of adsorption come into play when choosing a catalyst
. If adsroption is too strong then the product cannot be released such as with W
.If adsorption is too weak then the reactants do not adsorb in a high enough concentration such as with Ag
What shells are used when making adsroption bonds
3d and 4S
What are the steps for hetrogenous catalysis
.Reactant form bond at active site
.Bond weakens in reactants and break
.New bond forms between reactants held close together on surface
.This weakens bonds between product and catalyst and product leaves
Give the equations of the 2 steps for the contact process
SO2 +V2O5 > SO3 + V2O4
2V2O4 + O2 > 2V2O5
What is catalytic poisoning and give examples
Catalysts can become poisoned by impurities and consequently have reduced efficiency
There can be poisoining by sulfur in the contact process and also lead in a catalytic converter, which means they lose their efficiency and need to be replaced, leaded petrol cannot be used in cars fitted with a catalytic converter because the lead will adsorb onto the surface of the catalyst
What occurs when the catalyst and the reactants are in the same phase
The reaction will proceed through an intermediate species, this will often have a different oxidation state, and at the end of the reaction the original oxidation state will occur again
Why can transition metals pose as catalysts
They can form variable oxidation states, they are ale to donate and recieve electrons and can oxidise and reduce, this is because the ions contain partially filled d sub shells that can easily lose or gain electrons
Why is the uncatalysed reaction bhetween iodide and persulfate ions slow
The reaction needs a collision between two negative ions, repulsion is high and the ions are going to hinder this, this causes the reaction to have a high activation energy
What importance does the electrode potential play in choosing a suitable homogenous catalyst
The electrode potential needs to lie in between the electrode potential of the two reactants, it will first reduce the reactant with the more positive electrode and then it will oxidise the reactant with the more negative electrode
What is autocatalysis
When one of the products of the reaction can catalyse the reaction
Give the catalysed route for the reaction of ethanedioate ions and manganate ions
4Mn2+ + MnO4- + 8H+ > 5Mn3+ + 4H2O
2Mn3+ + C2O4- > 2Mn2+ +2CO2
Why is the reaction between ethanedioate and managanate ions intially slow and then fast
Because the collision betwen the two negative ions which repel eachother leading to a high activation energy
The Mn2+ ions that are produced act as an autocatalyst and the reaction speeds up as MnO4- concentration drops
How can you follow the reaction rate of manganate and ethanedioate ions
Remove samples at set times, titrate to work out the concentration of the MnO4-
Use spectrometer to measure the intensity of the purple colour, does not distrupt the reaction mixture and leads to a much quicker determination of the concentration
How would you construct a catalysed mechanism for a reaction
.Split the full equation into 2 half equations- redox
. Make the oxidation equation for catalyst and then add it to the original reduced equation
.Use the reduced equation for catalyst and add to the original oxidised equation
.For fact check you can make sure that the 2 equations add up to the original full non catalysed equation
What is the colour of silver linear complexes
Colourless
Why is silver not a transition metal
It behaves likes transtion metals as it can from complexes and show catalytic behaviour but it does not have variable oxidation states and does not form coloured compounds
This is because silver complexes have a +1 oxidation state with a full 4d subshell in both its atom and ion, it is not a transtion metal by definition and cannot do electron transitions between d orbitals
How do you use silver nitrate to work out the formula of chloride containing complexes
Silver nitrate will only be able to react with chloride ions that are not contained within the complex, and this can allow us to work out the amount of chlorines
