Transition Metals Flashcards
Define a Transition Metal
An Element which forms at least one stable ion with partially filled D-Sub Shell of electrons
Found within the d block
Where are Transition Metals located in the periodic table
part of the D-Block
In the middle (Ti- Cu)
What are some physical properties of transition metal (4)
Metallic
Good Conductor son heat and electricity
High Melting and boiling points
Strong,Shiny and Hard
What are some Uses of:
1) Iron
2) Titanium
3) Copper
1) Vehicle Bodies, To reinforce concrete
2) Aeronautical Parts Very strong and light
3) Cheap Wiring and plumbing
What’s are the chemical properties of transition Metals (4)
Variable Oxidisation States
Coloured Compounds/ Ions in solution
Good Catalysts
Forms Complex ions
Define the Term Complex Ion (2)
Central transition metal ion
Surrounded by ligands that are coordinately bonded (covalently) to it
Give examples of transition metal catalysts and the processes they Catalyse (3)
Iron - Haber Process
Vanadium (V) Oxide - Contact Process
Manganese (IV) Oxide - Decomposition of hydrogen peroxide
Which sub shell is emptied first when transition metals form ions
4s orbital
Define the Term Ligand (4)
An ion or molecule
with at least 1 lone pair of electrons
that donates the electrons to a transition metal ion
to form a coordinate bond & create a transition metal complex
Define the Term Unidentate ligand
A Ligand that donates 1 electron pair to form 1 coordinate bond to the central metal ion (only 1 lone pair to donate)
Define the Term bidentate ligand
A Ligand that donates 2 pairs of electrons to form two coordinate bonds to the central metal ion ( 2 lone pars to donate)
Define the Term Multidentate ligands
A Ligand that donates 3 or more electron pairs to form 3 or more coordinate bond to the central metal ion
Give some examples of monodentate ligands (4)
Cl-
H2O
NH3
CN-
Draw Ethanedioate ligand
Bidentate Ligand
Draw Benzene-1,2-diol Ligand
Bidentate Ligand
Draw an ethane-1,2-diamine ligand
Bidentate ligand
Define the term coordination Number
The number of coordinate bonds the metal ion has formed to surrounding ligands
What is the Chelate Effect (3)
Chelate Complexes with mulidentate ligands are favoured over ligands that are monodentate or bidentate ligands
more lone pairs per molecule
as it is a entropically favourable reaction
more moles of molecules on products then reactants
Explain the Chelate effect on ions in terms of entropy and the reaction that is occurring
Number of molecules increases when multidentate ligands displaces other ligands
that form fewer coordinate bonds with the central metal ion per molecule
so the products has more moles of molecules then products
entropically favorable
What ion is usually formed when a transition metal compound is dissolved in water
Draw an example
What is its Shape
If a transition metal ion has 2 ligands, which shape is it usually
Linear
180 Degrees
If a transition metal ion has 4 ligands
What shapes can it be
Tetrahedral
Square Planar
What shape is a complex ion if it has 6 ligands
Octahedral
How can Complex ions display E-Z isomerism (geometric)
What shapes does it apply to
Square Planar or Octahedral shapes
Where the metal complex has 2 or more ligand types
If the two high priority ligands are on the same side of the molecule this forms an E or cis- isomer (Reflection on x=O)
If the two high priority ligands are on opposite sides of the molecule this forms an z or trans- isomer
(Reflection on y=O)
What happens to Co2+ ,Cu2+ and Fe3+ ‘s coordination numbers when Cl- Ligands replace NH3 or H2O ligands
Coordination numbers decrease from 6 to 4
Cl- is a much larger ligand then H2O or NH3
Therefore the shape changes to tetrahedral or square planar
What is haem- (6)
A molecule which makes up protein chains
with an Fe2+ central metal ion
Complex has a coordination number of 6
4 of the coordinate bonds are to a ring system called porphyrin
1 is to the nitrogen of a globin (protein)
1 is to an oxygen in an O2 molecule
How does haemoglobin transport oxygen
O2 forms weak coordinate bond to the metal ion, then is transported around the body. The bond breaks when haemoglobin reaches cells and oxygen is released.
Why is Carbon monoxide toxic (3)
CO coordinator bonds to the Fe2+ within haem- that is very strong
It’s coordinately bonded more strongly then O2 or H2O to the central metal ion
Stops O2 from bonding to haemoglobin so O2 cannot be transported around the body.
Why are transition metal compounds coloured (6)
TM Ions have Partially filled D orbitals
When ligands are coordinately bonded to form complexes the d orbitals are split into different energy levels
For electrons to excite to a higher energy level energy in the form of photons is absorbed
Within TM the photons absorbed have a frequency within the visible light spectrum, as the photons energy must have the same energy as the energy gap between the split d subshells
The frequency of visible light absorbed is not visible to receptors
meaning a complimentary colour is visible made up of all colours not absorbed
What affects the colour of a transition metal compounds (3+1)
Type of Ligand
Shape of complex
Oxidisation state of the metal ion
All change the Energy gap between the split d orbitals
What can you use to reduce vanadium
Zinc
What colour is Fe2+
Pale Green
What colour is Fe3+
Pale Brown
What colour is Ni2+
Green
What Colour is Cr3+
green/Violet
more violet when its its aqua ion
What colour is Co2+
pink
What colour is Cu2+
Blue
What does a colorimeter do
Measures absorbance of a particular wavelength of light by a solution
What information does a colourimeter give you
The concentration of a certain ion in the solution
Why can transition metal form variable oxidisation states
Ions formed have partially filled d-orbitals
so loose electrons in the 4s and then 3d electrons
Which oxidation states do all transition metals have (except scandium)
+2
Due to loss of 2 electrons from 4s orbital
Tollens Reagent
Gentle oxidising agent
Used as a test for aldehydes ( Silver mirror formed with aldehyde)
silver 2 complex ions are reduced to form solid silver Precipitate
when in the presence of a molecule that can be oxifdised
What colour is MnO4- ions?
Deep Purple
What colour is a Mn2+ ion
Pale Pink
(Too faint to usually detect on a colorimeter)
Write the half equation for the reduction of MnO4- to Mn2+
MnO4- + 8H+ +5e- ———>. Mn2+ + 4H2O
Why are redox titrations with transition metals said to be self indicating
They often involve a colour change as the metal is changing oxidisation stage
What colour Cr2O7 2- ion
Orange
What Cr3+
Green
Write a half equation for the reduction of Cr2O7 2- to Cr3+
Cr2O7 2- + 14H+ +6e- ————> 2Cr3+ +7H2O
What happens to aqua metal ions in acidic conditions
They get reduced to a lower oxidation state
what happens to aqua metal ions in alkaline conditions
they get oxidised
What value signifies how readily will a metal ion reduce/ oxidise
E Cell values
More positive —> higher tendency to reduce
More negative —-> higher tendency to oxidise
What changes the E Cell value of a TM metal ion complex
Ph, Ligands involved
Define a Catalyst
A Substance that increases the rate of reaction via an alternate reaction pathway at lower activation energy without itself or any substance changing chemically
Why are Transition Metals Good Catalysts
They Exist in variable Oxidation states
to provide more alternate reaction pathways for the reaction to potentially follow
Why are Group 1,2,3 metals not as good catalysts as TM
They only exist in 1 oxidation state
What are the advantages to using a catalyst in a reaction
Increases rate of reaction —-> lower activation energy —-> more particles above activation energy
Allows reaction at lower temperatures —> saves energy and resources
What metals are used in a catalytic converter
What are the reactions they catalyse
Platinum, Palladium, Rubidium
Define heterogeneous Catalyst (2)
A Catalyst that is in a different phase to the reactants
Catalyst activity occurs on the catalysts surface as the reactants pass over it
What is an advantage of using a heterogenous catalyst over homogeneous
Catalyst is easily separated from products
How do heterogenous catalysts work
Reactants adsorb to the catalysts surface at active sites
This weakens the bonds within the reactants
the reactants are then held close together in the correct orientation to react
After reaction has occurred the products desorb from the active sites
For a heterogeneous catalyst to be considered good, what properties must it have (3)
reactants cant adsorb too strongly to the active sites - otherwise products wont desorb
reactants cant adsorb too weakly to the active sites - otherwise products wont be held for long enough for a reaction - bonds wont be sufficiently weakened
Need a good balance between desorption and adsorption
How do you increase the efficiency of heterogeneous catalyst (2)
Increase surface area — Increases number of active sites present
Spread catalyst onto an inert surface —- increase the surface/mass ratio eg. ceramic honeycomb
What is Catalyst poisoning
Unwanted impurities adsorb to the catalyst active sites too strongly
cannot desorb
This Block the active sites on the catalysts surface for the reactants to bind to
What effect does catalyst poisoning have on catalytic activity
Decreases the effectiveness of the catalyst over time, as more active sites are blocked by impurities
How can the effectiveness of a heterogeneous catalyst reduce other then catalyst poisoning
Finely divided catalyst can be gradually lost from their support surface
Write the equation for the haber process, what is its conditions and catalyst
N2(g) + 3H2 (g) ——> 2NH3 (g)
Iron catalyst
400-450 degrees c
200atm
How does the catalyst in the haber process get poisoned
The iron catalyst gets poisoned by sulphur impurities in the gas streams
as methane is used for the production of hydrogen gas, which contains sulphur impurities
Write the overall equation for the contact process, what is its catalyst and conditions
1-2 atm
450 degrees c
What are the 4 reactions that are involved in the contact process
3) SO3 + H2SO4 –> H2S2O7
4) H2S2O7 + H2O —> 2 H2SO4
Why is vanadium (v) oxide good catalyst in the contact process
Can change oxidation state between 5+ and 4+
so can be reused
Define homogeneous catalyst (4)
A catalyst that is in the same phase as the reactants
by forming an intermediate
creating a different reaction pathway with a lower activation energy
after intermediate is formed the original catalyst is reformed
How do homogeneous catalysts work
Form Intermediates that give a different reaction pathway with lower activation energy
What is the overall reaction between S2O8 2- and I- ions
(no catalyst)
Why does the reaction between S2O8 2- ions and I- ios have a high activation energy in normal conditions
Two negative ions are reacting
they repel each other
so Ea is high
What is the overall reaction between S2O8 2- and I- ions
(both reactions + fe2+ catalyst)
Define the term autocatalysis
When a product of a reaction is also catalyses the original recation
Homogeneous Catalyst
Draw and explain a concentration of reactant against time graph for an auto catalysed reaction
Write the half equations for the conversion of C2O4 2- ions to CO2
Write the combined half equation for the reaction between C2O4 2- and MnO4- ions
In this reaction how does Mn2+ autocatalyse the original reaction
Mn2+ is oxidised then reduced
total oxidation state of the metal complex (overall charge)
oxidation state of metal + total oxidation state of ligands
What is a lewis base?
Lone pair donors
What is a lewis acid?
Lone pair acceptor
How to you create a colourimeter calibration graph
Absorption (y axis) varying known concentrations of transition metal solutions (x axis) is tested and plotted on a graph.
What is a complimentary colour
Colour formed through the mixture of all visible light wavelengths that are not absorbed.
Draw and explain the complimentary colour wheel
Find what colour the TM absorbs
Opposite to it is the complimentary colour
Draw a cis- isomer for [Co (H2O)4 Cl2]
Draw a trans- isomer for [Co (H2O)4 Cl2]
Why is scandium and zinc not considered transition metals?
Sc3+ has an empty d subshell not partially filled so not a TM
Zn2+ has a full d subshell not partially filled so not a TM
Explain why different TM complex ions have different colours (3)
In different complexes the energy gap between the split d orbital differs
When an electron is excited by absorbing energy
Different wavelengths in the visible light spectrum are absorbed, producing a different complimentary colour to a light receptor
Why would a positive intermediate increase the rate of the overall reaction between 2 negative ions
The positive intermediate formed attracts the negative ions, decreasing the activation energy.
Write an Equation for the reaction between 1,2- Diaminoethane and a Cu(NH3)4.(H2O)2 complex
Why is the enthalpy change approximately zero
4 Cu-N coordinate bonds are broken
4 Cu-N coordinate bonds are made after the ligand substitution
Both have very similar enthalpy resulting in an approximate zero enthalpy change
What is the structural formula for 1,2- diaminoethane
H2N H2C CH2 NH2
Symmetrical molecule
For a reaction between 1,2- Diaminoethane and a Cu(NH3)4.(H2O)2 complex
It has an approximately zero enthalpy change
Explain why the reaction occurs anyway
Chelate Effect
3 Particles react to form 5 particles
Disorder has increased so entropy change is positive
As free gibbs = Enthalpy change - T(Entropy Change)
It gives a negative free gibbs so the reaction is feasible
What is the written complex for Silver (ii) Nitrate
[Ag(NH3)2]+
1) See below
2) What property must an impurity within sample x have for the calculate mass to be larger then expected
1) Find out charge of TM ion
SO4 = 2-
H2O = 0
So Fe = 2+
Construct two half equations and combine them to form a redox equation (Equation for reaction)
2) Impurity must be a reducing agent that reacts with the dichromate
Manganate would oxidise the Cl- ions
Because the E Cell for Manganate (VII) is more positive then the Ecell for Cl2
1.51 - 1.36 = 0.15 (Cl2 equation flipped but ECell is the same)
Meaning its a feasible reaction
Write an equation between manganate (VII) ions and ethandioate ions in acidic conditions
Why can you use a colorimeter to measure the concentration of Manganate (VII) ions
Ethandioate is oxidised to 2CO2
Acidic conditions means lots H+’s to react
2) Consider the properties of products and reactions
Only Manganate(VII) ions are distinctly coloured
Mn2+ ions are plane pink and are too faint to detect.
On a Concentration against time curve
What part of it shows an auto catalysed reaction
Reaction starts of slow shown by a shallow gradient
Then the rate gets faster shown by a Gradient increasing
For a Reaction between manganate (VII) ions and ethandioate ions in acidic conditions
Identify the AutoCatalyst
Write Two Equations to show how the autocatalyst is involved
1) Mn2+ ions
2) Write equation between original reactant and autocatalyst forming the intermediate
Next equation show how the intermediate is reduced and the ethanedioate is simultaneously oxidised in a redox reaction
A & C appear to have a reduction in oxidation state
however Both molecules of CrO4 2- have an os state of 6
6x2 = 12
12=12
so A is the only one reduced
Explain what colour and why do Aqueous Solutions containing [CuCl4]2-appear coloured (1+2)
Yellow/PaleBrown
Only Particular light wavelengths absorbed, this excites electrons
Only Yellow light is transmitted which is a complimentary colour consisting of all non absorbed wavelengths
What oxidation state is EDTA ligand?
4-
Explain why colourimetery cannot be used to identify the concentration of solutions containing [CuCl2]-
For this to occur Cu metal ion has to have an oxidisation state of 1
a Cu+ ion has a full 3d sub shell of electrons, as the 1 electron in the 4s orbital is emptied first.
This means that there is no split d orbital
So The metal ion appears colourless as it cannot absorb frequencies of visible light
