Transition Metals ( A-level only) Flashcards
What cause the characteristics of elements Sc –> Cu arise?
From an incomplete d sub-level in atoms or ions
What are the characteristics of transition metals?
- complex formation
- formation of coloured ions
- variable oxidation
- catalytic activity
Why is zinc not a transition metal?
- zinc only forms a +2 ion
- has a complete d orbital
What rule does Cu and Cr follow in the electronic configuration?
- fill the 3d subshell fully and then 4s
What is a ligand?
molecule or ion that forms a co-ordinate bond with a transition metal by donating a pair of electrons
What is a complex?
A central metal ion surrounded by ligands
What is a co-ordinator number?
the number of co-ordinate bonds to the central metal atom or ion
What is co-ordinate bonding?
when shared pair of electrons in the covalent bond come from only one of the bonding atoms
What is monodentate?
one co-ord bond per ligand
What is bidentate?
two atoms with lone pairs can form two-co ordinate bonds per ligand
What is multidentate?
can form multiple coridante bonds per ligand
What is an example of a monodentate ligand/
H20, NH3, and CL-
What is an example of a bidentate ligand?
Ethanedioate
C2O4.2-
Ethane-1,2-diamine
NH2CH2CH2NH2
What does the bracket [] and () mean for transition metals?
[] - complex
() - ligand
What can H2O, NH3 and Cl− act as in transition metals?
Monodentate ligands
What is similar about ligands NH3 and H20?
Similar in size and uncharged
Will the co-ordination number change if NH3 replaces H20 ligand?
- no as they are similar
What may be the problem when NH3 replaces H20 ligand using Copper?
[Cu(H2O)6]2+(aq) + 4NH3 (aq)
May be incomplete so produces [Cu(NH3)4(H2O)2]2+
What is the difference between the chloride ligands and other monodentatae ligands?
- larger than the uncharged ligands H20 and NH3
What does the addition of high concentration of chliride ions to an aqueous ion cause?
Ligand substitution reaction
Formula of complex and colour: conc HCL to Cu
[CuCl4]2- yellow/green solution
Formula of complex and colour: conc HCL to Co
[CoCl4]2- blue solution
What are the two Bidentatae ligandsa and co-ordination number 6?
ethane-1-2-diamine
ethanedioate
What is the formula for ethane-1-2-diamine?
[Cr(NH2CH2CH2NH2)3]3+
What is the formula for ethanedioate?
[Cr(C2O4)3]3-
What is an example of a multidentate?
EDTA.4-
Describe how CO binds to haem?
- toxic
- can form a strong co-ordinte bond with
haemoglobin - stronger bond than oxygen
- replaces oxygen
- attaching to haemoglobin
What is the Chelate effect?
bidentate/multidentate ligands substitute monodentate ligands
–> increases moles of products
–> increases entropy
–> highly feasible
What will make Free energy negative with the formula?
The entropy will be negative
Enthalpy is small
What is the mole ratio of EDTA with any metal ion?
1:1
What is the common shape that transition metal ions form?
octahedral complexes with small liagnds
What shape of complex does Cl- ligands form?
Tetrahedral
- larger so less space
What shape of complex ion is cisplatin?
Square planar
What shape of complex ion does Ag+ form?
Linear
What isomerism can complexes show?
Cis-trans isomerism
Optical isomerism
Cis isomerism is when the molecules are on the ____ side
Same
Trans isomerism is when the molecules are on the ______ side
different
Which ligands show cis-trans isomerism?
Monodenatate
What type of ligands show optical isomerism?
Bidentate ligands
What are optical isomers?
Non-superimposable mirror images
Colour changes arise from changes in?
- oxidation state
- co-ordination number
- ligand
Why do transition metals form coloured complexes?
- 5d orbitals split into different energy levels
- Frequency of light is absorbed to excite the electrons from ground state to an excited state
- Frequency of light that is not absorbed is that colour that we see
What are the two equations for the amount of energy absorbed due to light?
Delta E = h x v
h= plancks constant (J s)
v= frequency ( unit s-1)
Delta E = hc/λ
c= speed of light 3.00 x 10^8
λ = wavelength of light absorbed
How does altering the ligand or co-ordination number cause a colour change?
- alter the energy split
- between the d -orbitals
- changes the Energy absorbed
- hence change the frequency of light absorbed
Why does Sc^3+ not have colour?
- ion hasnt got any D-block electronds left to move around
- no energy transer equal to that visble of light
Why does Zn^2+ amd Cu^+ not show colour?
their electronic shell is full
no space for electrons to transfer
no transfer of energy equal to visible light
Describe the method of spectroscopy
- Add an appropriate ligand to intensify colour
- Make up solutions of known concentration
- Measure absorption or transmission using colorimeter
- Plot graph of absorption vs concentraiton
- Measure absorption of unknown and compare
What is variable oxidation?
one element can exist in a range of oxidation states
What influences the redox potential for a transition metal ion changing from a high to low oxidation state?
pH and ligand
How many oxidation states does vanadium has?
Four main oxidation states
What vandium ion has a +4 oxidation state?
VO^2+
Which vanadium ion has vanadium’s oxidation state as +5?
VO2^+
What colours are the four main oxidation states for vanadium?
remember mnemonic
YOU BETTER GET VANADIUM
VO2+ Oxidation state +5 ( a yellow solution)
VO2+ Oxidation state + 4 (a blue solution)
V3+ Oxidation state + 3 (a green solution)
V2+ Oxidation state + 2 (a violet solution)
What will happen in the addition of zinc to vanadium (V) in acidic solution?
Reduces the vanadium
down through each successive oxidation state
yellow blue green violet/purple
What does zinc act as in the reaction with vanadium (V) in acidic solution?
Strong reducing agent
can reduce most transition metals from high oxi state to low oxi state
How does the tollenes test work in reference to [Ag(NH3)2]+?
- used to distingush aldehyde and ketone
- reduction of [Ag(NH3)2]+ by aldehydes to make silver
What is the manganate ion?
MnO4-
What is the maganese ion usually used in redox titrations?
Mn2+
What is the half equation for maganate oxide?
Mn04- + 5e- + 8H+ —-> Mn2+ + 4H20
What is the inital colour of Maganate?
Purple
What is the final colour of manganate that should be seen in the flask when reduced in titration?
Pale pink/colourless
What are the two ions used in redox titrations for maganate?
Fe2+
C2O4^2-
What is the half equation for Fe2+?
Fe2+ —-> Fe3+ e-
What is the half equation for C2O4^2-
C2O4^2- —-> 2CO2 + 2e-
What acid do you use for manganate titrations and why?
Dilute sulfric acid to supply the 8H+ ions. Does not set up alternative redo reactions.
What happens if insufficent acid is added to managante titration?
Causes production of MnO42 than Mn2+
it will mask the colour change and lead to greater volume of manganate being added the titration
Why is concentrated HCL not a acid used in manganate redox titration?
It cannot be conc HCl as the Cl-
ions would be oxidised to Cl2 by MnO4-
- the EMF for MnO4- is greater that CL-
- greater volume of manganate being used and posionius Cl2 is made
Why can’t nitric acid be used as a acid in redox titrations?
It acts as oxidising agent for Iron.
Fe2+ –> Fe3+
Leads to smaller volume of manganate being used as less concentration of Fe2+ as it has reacted already.
What is the half equation for hydrogen peroxide?
H2O2 —> O2 + 2H+ 2e-
Why is heat added to reaction of C2O4^-2 and MnO4-?
Both ions are negative so naturally repel
slow reaction
heat increases the rate
What acts as a catalyst in MnO4- redox titration with C2O4-?
Mn2+
production speeds up the rate of reaction –> autocatalysis
faster colour change as time goes on
How do catalysts increase the rate of reaction?
Providing an alternative pathway with a lower activation energy
What is a heterogenous catalyst?
Is in a different phase from the reactants
What is a homogenous catalyst?
The same phase as the reactants
Where does reaction occur with heterogenous catalysts?
Usually at the surface of the catalyst
Describe the steps in heterogenous catalysis?
- Reactants form bonds with atoms at active sites on the surface of the catalyst so They are adsorbed.
- As a result bonds in the reactants are weakened and break
- New bonds form between the reactants held close together on a catalyst
- This weakens bonds between product and catalyst and product desorbs
How does surface area help Catalysts?
Improve its effectiveness
Support medium used to maximise surface area and minimise cost
How does iron catalyst in Haber process work efficiently
Used in pea sized lumps so larger surface area or support medium
How can catalyst become poisoned?
By impurities
Meaning active sites are then blocked
