2.5 Transition Metals Flashcards
What do transition metal characteristics of elements Sc -> Cu arise from?
Transition metal characteristics of elements Sc -> Cu arise from an incomplete d sub-level in atoms or ions.
What are the 4 characteristics of transition metals?
- Complex formation
- Formation of coloured ions
- Variable oxidation states (Cr2+, Cr+)
- Catalytic activity
Draw the electronic configuration of the element Sc and its ion Sc3+
(see page 1 in the chemrevise revision guide)
Draw the electronic configuration of the element Ti and its ion Ti3+
(see page 1 in the chemrevise revision guide)
Draw the electronic configuration of the element V and its ion V3+
(see page 1 in the chemrevise revision guide)
Draw the electronic configuration of the element Cr and its ion Cr3+
(see page 1 in the chemrevise revision guide)
Draw the electronic configuration of the element Mn and its ion Mn3+
(see page 1 in the chemrevise revision guide)
Draw the electronic configuration of the element Fe and its ion Fe3+
(see page 1 in the chemrevise revision guide)
Draw the electronic configuration of the element Co and its ion Co2+
(see page 1 in the chemrevise revision guide)
Draw the electronic configuration of the element Ni and its ion Ni2+
(see page 1 in the chemrevise revision guide)
Draw the electronic configuration of the element Cu and its ion Cu2+
(see page 1 in the chemrevise revision guide)
Draw the electronic configuration of the element Zn and its ion Zn2+
(see page 1 in the chemrevise revision guide)
Why is Zn not a transition metal?
Zn can only form a +2 ion. In this ion the Zn2+ has a complete d orbital and so does not meet the criteria of having an incomplete d orbital in one of its compounds.
Give the definition of a complex.
A complex is a central metal ion surrounded by ligands.
Give the definition of a ligand.
A ligand is an atom, ion or molecule which can donate a lone electron pair to a metal.
Draw Cu’s complex with water.
(see page 1 in the chemrevise revision guide)
What is Ni used as a catalyst for?
Ni is a catalyst in margarine production.
What is V2O5 used for?
V2O5 is used for making SO3 for H2SO4
What are Pt and Pd used as?
Catalytic converters
N2O + CO2 -> N2 + CO2
Reactants are toxic in the air because they react together, they’re used in car exhausts to make it less toxic.
What is 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 co-ordination number is the number of co-ordinate bonds formed to a central metal atom.
(not ligands because some ligands can form 2 bonds)
What are monodentate ligands?
Ligands can be mono dentate (e.g. H2O, NH3 and Cl-) which can form on co-ordinate bond per ligand.
What are bidentate ligands?
Ligands can be bidentate (e.g. NH2CH2CH2NH2 and ethanedioate ion C2O42-) which have two atoms with lone pairs and can form two co-ordinate bonds per ligand.
What are multidentate ligands?
Ligands can be multidentate (e.g. EDTA4- which can form 6 co-ordinate bonds per ligand)
Write the equation for the exchange of ligands NH3 and H2O with Co2+ and Cu2+
(see page 1 in the chemrevise revision guide)
What does the addition of a high concentration of chloride ions (from conc HCl or NaCl) to an aqueous ion lead to?
A ligand substitution reaction
Which ligand exchange involves a change in co-ordination number?
- Cl-
- H2O
- NH3
The Cl- ligand is larger than the uncharged H2O and NH3 ligands so therefore ligand exchange can involve a change of co-ordination number.
Read the box labelled R on page 1 in the chemrevise revision guide.
Understand it?
If solid copper chloride (or any other metal) is dissolved in water what does it form?
It forms the aqueous [Cu(H2O)6]2+ complex and not the chloride [CuCl4]2- complex.
Are all ligands Lewis bases?
Yes, all ligands are Lewis bases.
Is ethane-1,2-diamine a monodentate or bidentate ligand?
ethane-1,2-diamine is a common bidentate ligand.
Draw the complex of Ethane-1,2-diamine with Cr and write the structural formula for it.
What is its co-ordination number?
There are 3 bidentate ligands in this complex each bonding in twice to the metal ion.
It has a co-ordination number of 6.
(see page 2 in the chemrevise revision guide)
Is ethanedioate a monodentate or bidentate ligand?
ethanedioate is a bidentate ligand.
Draw the complex of Ethanedioate with Cr and write the structural formula for it.
What is its co-ordination number?
(see page 2 in the chemrevise revision guide)
Write the equation for the formation of the ethane-1,2-diamine bidentate ligand.
(see page 2 in the chemrevise revision guide)
Write the equation for the formation of the ethanedioate bidentate ligand.
(see page 2 in the chemrevise revision guide)
When would a partial substitution of ethanedioate occur?
Partial substitution of ethanedioate may occur when a dilute aqueous solution containing ethanedioate ions is added to a solution containing aqueous copper(II) ions. In this reaction four water molecules are replaced and a new complex is formed.
Draw the complex that is formed when partial substitution of ethanedioate ions occurs.
(see page 2 in the chemrevise revision guide)
Write the equation for the partial substitution of ethandioate ions.
(see page 2 in the chemrevise revision guide)
Draw the displayed formula for EDTA4-
not really necessary to learn off by heart, but good to know
(see page 2 in the chemrevise revision guide)
How many donor sites does EDTA4- have?
6 donor sites (4O and 2N) and forms a 1:1 complex with metal(II) ions.
Is Haem monodentate or bidentate ?
Trick question, Haem is an iron(II) complex with a multidentate ligand.
Write the formula for the formation of an EDTA4- complex.
(see page 2 in the chemrevise revision guide)
How is oxygen transported in the blood in haemoglobin?
Oxygen forms a co-ordinate bond to Fe(II) in the haemoglobin, enabling oxygen to be transported in the blood.
Why is CO toxic to humans?
CO is toxic to humans as CO can form a strong co-ordinate bond with haemoglobin. This is stronger than that made with oxygen and so it replaces the oxygen attaching to the haemoglobin.
Describe what is meant by the chelate effect.
The substitution of monodentate ligand with a bidentate or multidentate ligand leads to a more stable complex.
This chelate effect can be explained in terms of positive entropy change in these reactions as more molecules of products than reactants.
Why is there an increase in entropy in the formation of the multidentate ligand EDTA2-?
The copper complex ion has changed from having a unidentate ligand to a multidentate ligand. In this reaction there is an increase in the entropy because there are more moles of products than reactants (from 2-7), creating more disorder.
(see page 3 in the chemrevise revision guide
for the equation)
Why is the enthalpy change small in the formation of the multidentate ligand EDTA2-?
There are similar numbers of bonds in both complexes.
(see page 3 in the chemrevise revision guide
for the equation)
Would the free energy ∆G be positive or negative?
Free energy ∆G would be negative as ∆S is positive and ∆H is small.
(see page 3 in the chemrevise revision guide
for the equation)
What are the uses of the EDTA complexes?
- Added to rivers to remove poisonous heavy metal ions as the EDTA complexes are not toxic.
- In many shampoos to remove calcium ions present in hard water, so helping lathering.
Why is there an increase in entropy in the formation of the bidentate ligand ethane-1,2-diamine?
This reaction has an increase in entropy because of the increase in moles from 4-7 in the reaction.
∆S is positive.
Why is the enthalpy change close to zero in the formation of the bidentate ligand ethane-1,2-diamine?
Its enthalpy change ∆H is close to zero as the number of dative covalent and type (N to co-ordinate bond) are the same so the energy required to break and make bonds will be the same.
Would the free energy ∆G be positive or negative?
Free energy ∆G would be negative as ∆S is positive and ∆H is small.
The complex formed is stable
(see page 3 in the chemrevise revision guide
for the equation)
Answer the exam question labelled 1 on page 3 in the chemrevise revision guide.
correct?
Draw the shape of the complex of Ni with NH3.
Transition metal ions commonly form octahedral complexes with the small ligands (e.g. H2O and NH3)
(see page 4 in the chemrevise revision guide)
Draw the shape of the complex of Cu with H2O.
Transition metal ions commonly form octahedral complexes with the small ligands (e.g. H2O and NH3)
(see page 4 in the chemrevise revision guide)
Draw the shape of the complex of Cu with Cl.
Transition metal ions commonly form tetrahedral complexes with larger ligands. (e.g. Cl)
(see page 4 in the chemrevise revision guide)
Draw the shape of the complex of Pt with Cl and NH3.
(see page 4 in the chemrevise revision guide)
Draw the shape of the complex of Ag with NH3.
(see page 4 in the chemrevise revision guide)
Draw the 2 types of isomerism of the complex of Ni with NH3 and Cl.
(see page 4 in the chemrevise revision guide)
Draw the 2 types of isomerism of the complex of Cr with Cl and H2O.
(see page 4 in the chemrevise revision guide)
Draw the 2 types of isomerism of the complex of Ni with ethane-1,2-diamine.
(see page 4 in the chemrevise revision guide)
Draw cisplatin
(see page 4 in the chemrevise revision guide)
What 3 changes do colour changes in complexes arise from?
- oxidation states
- co-ordination number
- ligand
Look at the colour changes on the top of page 5 in the chemrevise revision guide.
understand?
How does colour arise in transition metals?
Colour arises from electronic transitions from the ground state to excited states: between 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.
How do you calculate the energy difference between split orbitals?
∆E = hv
v = frequency of light absorbed (unit s-1 or Hz) h = Planck's constant 6.63x10-34 (J s) ∆E = energy difference between split orbitals (J)
If a solution absorbs orange light what will the colour appear to be?
A solution will appear blue if it absorbs orange light. The energy split in the d orbitals ∆E will be equal to the frequency of orange light (5x1014s-1) x Planck’s constant ∆E in a blue solution = hv
(see page 5 in the chemrevise revision guide)
What would changing the ligand or changing the co-ordination number do to the colour appeared?
Changing the ligand or changing the co-ordination number will alter the energy split between d orbitals, changing ∆E and hence change the frequency of light absorbed.
Why has Sc3+ not got any colour?
Scandium is a member of the d block. Its ion (Sc3+) hasn’t got any d electrons left to move around. So there is not an energy transfer equal to that of visible light.
Why has Zn2+ and Cu+ not got any colour?
The d shell is full (e.g. 3d10) and so there is no space for the electrons to transfer. Therefore there is not an energy transfer equal to that of visible light.
Describe what spectrophotometry is and what its method is.
(see page 5 in the chemrevise revision guide)
What are the 3 general trends of variable oxidation states across the period of transition metals?
- 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+ and Fe2+
What is the redox potential for a transition metal ion changing from a higher to a lower oxidation state influenced by?
The redox potential for a transition metal ion changing from a higher to a lower oxidation state is influenced by pH and by the ligand.
What are vanadium’s 4 main oxidation states?
What are the colours of its solution?
(see page 6 in the chemrevise revision guide)
What is [Ag(NH3)2]+ used in?
Tollen’s reagent.
see page 6 in the chemrevise revision guide
Why is the redox titration between Fe2+ with Mn(O4)- a self indicating reaction?
The redox titration between Fe2+ with Mn(O4)- (purple) is a very common exercise. This titration is self indicating because of the significant colour change from reactant to product.
Write the equation for the redox titration between Fe2+ with Mn(O4)-
(see page 6 in the chemrevise revision guide)
What is the problem with filling the burette with manganate?
The purple colour of manganate can make it difficult to see the bottom of the meniscus in the burette.
What acid should you use for manganate titrations?
Only use dilute sulfuric acid for manganate titrations.
What will insufficient volumes of sulfuric acid in a manganate titration lead to?
Why is this a problem?
Write the equation for this reaction.
Insufficient volumes of sulfuric acid will mean the solution is not acidic enough and MnO2 will be produced instead of Mn2+.
The brown MnO2 will mask the colour change and lead to a greater (inaccurate) volume of manganate being used in the titration.
(see page 6 in the chemrevise revision guide for equation)
What will using a weak acid like ethnoic acid in a manganate titration lead to?
Why is this a problem?
Same effect as insufficient volumes of sulfuric acid as it cannot supply the large amount of hydrogen ions needed (8H+):
Insufficient volumes of sulfuric acid will mean the solution is not acidic enough and MnO2 will be produced instead of Mn2+.
The brown MnO2 will mask the colour change and lead to a greater (inaccurate) volume of manganate being used in the titration.
What will using conc HCl in a manganate titration lead to?
Why is this a problem?
Write the equation for this reaction.
The Cl- ions would be oxidised to Cl2 by Mn(O4)- as the EºMn(O4)-/Mn2+ > EºCl2/Cl-
This would lead to a greater volume of manganate being used and poisonous Cl2 being produced.
(see page 6 in the chemrevise revision guide for equation)
What will using nitric acid in a manganate titration lead to?
Why is this a problem?
Write the equation for this reaction.
Nitric acid is an oxidising agent. It oxidises Fe2+ to Fe3+ as EºNO3-/HNO2 > EºFe3+/Fe2+
This would lead to a smaller volume of manganate being used.
(see page 6 in the chemrevise revision guide for equation)
Answer the example question labelled 1 on page 7 in the chemrevise revision guide.
correct?
Write the redox equation for the manganate titration with hydrogen peroxide.
(see page 7 in the chemrevise revision guide)
Write the redox equation for the manganate titration with ethanedioate.
(see page 7 in the chemrevise revision guide)
Answer the example question labelled 2 on page 7 in the chemrevise revision guide.
correct?
What is a heterogeneous catalyst?
A heterogeneous catalyst is in a different phase from the reactants.
What is a homogeneous catalyst?
A homogeneous catalyst is in the same phase as the reactants.
How do heterogeneous catalysts catalyse a reaction on its surface?
Absorption of reactants at active sites on the surface may lead to catalytic action. The active site is the place where the reactants absorb on to the surface of the catalyst. This can result in the bonds within the reactant molecules becoming weaker, or the molecules being held in a more reactive configuration. There will also be a higher concentration of reactants at the solid surface so leading to a higher collision frequency.
How can the strength of the absorption help to determine the effectiveness of the catalytic activity?
Some metals e.g. W have too strong absorption, and so the products cannot be released.
Some metals e.g. Ag have too weak absorption, and the reactants so not absorb in high enough concentration.
Will increasing the SA of a heterogeneous catalyst improve or decrease its effectiveness?
Increasing the SA of a solid catalyst will improve its effectiveness. A support medium is often used to maximise the SA and minimise the cost. (e.g. Rh on a ceramic support in catalytic converters)
Give the 4 steps in heterogeneous catalysis.
(see page 8 in the chemrevise revision guide)
Write the equation for V2O5 being used as a catalyst in the Contact Process.
(see page 8 in the chemrevise revision guide)
What is the catalyst V2O5 used for?
Catalyst in the Contact Process.
What is the catalyst CrO3 used for?
Used in the manufacture of methanol from CO and H
What is the catalyst Fe used for?
The Haber Process
Write the equation for Cr2O3 being used as a catalyst in the manufacture of methanol.
(see page 8 in the chemrevise revision guide)
Write the equation for Fe being used as a catalyst in the Haber Process.
(see page 8 in the chemrevise revision guide)
Catalysts can become poisoned by _______ and consequently have reduced ________
Catalysts can become poisoned by impurities and consequently have reduced efficiency.
Give two examples of how poisoning of catalysts can cost money.
- Poisoning by sulphur in the Haber process
- Poisoning of lead in catalytic converters in cars
Means that catalysts lose their efficiency and may need to be replaced.
Why can leaded petrol not be used in cars fitted with a catalytic converter?
Since lead strongly absorbs onto the surface of the catalyst.
When homogeneous catalysts are used, an intermediate species is used, what is an intermediate?
The intermediate will often have a different oxidation state to the original transition metal. At the end of the reaction the original oxidation will reoccur.
Why are transition metals able to act as homogeneous catalysts?
Transition metals can act as homogeneous catalysts because they can form various oxidation states. They are able to donate and receive electrons and are able to oxidise and reduce. This is because the ions contain partially filled sub-shells of d electrons that can easily lose or gain electrons.
Write the equation for the reaction between iodide and persulfate ions.
(see page 9 in the chemrevise revision guide)
Why is the uncatalysed reaction between iodide and persulfate very slow?
What is the catalyst used in this reaction?
The uncatalysed reaction is very slow because the reaction needs a collision between two negative ions. Repulsion between the ions is going to hinger this - meaning high activation energy.
Read the box labelled 1 on page 9 in the chemrevise revision guide.
understand?
Read the box labelled 2 on page 9 in the chemrevise revision guide.
understand?
Answer the example question on page 10 in the chemrevise revision guide.
correct?
Ag+ commonly forms ______ complexes.
Ag+ commonly forms linear complexes.
What are two similarities between silver and transition metals?
- Form complexes
- Show catalytic behaviour
What are two differences between silver and transition metals?
- Silver does not form coloured compounds
- Silver does not have variable oxidation states
What are all silver complexes’ oxidation states?
+1 with a full 4d subshell (4d10)
Look at the diagram labelled 1 on page 11 in the chemrevise revision guide.
Understand?
How do you use silver nitrate to work out formulae of chloride counting complexes?
(see page 11 in the chemrevise revision guide)
