Transition Metals Flashcards
Define ‘transition metal’
Forms at least one stable ion with a partially filled d-sub level
Are Scandium and zinc transition metals?
NO
What is special about Cu and Cr?
Their 4s only goes 4s1
What do the transition metals’ characters stem from?
Their partially filled d-sub level
What are the characteristics of transition metals?
Complex formation
Form coloured ions
Variable oxidation states
Catalytic activity
What is a ligand?
An electron pair donor
What is a complex?
A central metal ion/atom surrounded by ligands joined by coordinate bonds
What is coordination number?
The number of coordinate bonds to the central metal atom/ion
What is a coordinate bond?
When a molecule/ ion donates both the electrons from a lone pair to the empty orbital of another species
Define monodentate ligands
Donates one e- pair or forms one coordinate bond
Give the
a) Shape name
b) Bond angle
c) Occurrence
Of complexes with a coordination number of 2
a) linear
b) 180
c) Ag+ complexes
Give the
a) Shape name
b) Bond angle
c) Occurrence
Of complexes with a coordination number of 4
a) Square planar
b) 90
c) Pt2+ and Ni2+
Give the
a) Shape name
b) Bond angle
c) Occurrence
Of complexes with a coordination number of 4 when the ligands are too big to fit 6
a) tetrahedral
b) 109.5
c) eg Cl-
Give the
a) Shape name
b) Bond angle
c) Occurrence
Of complexes with a coordination number of 6
a) octahedral
b) 90
c) most complexes with small ligands (eg H2O and NH3)
Give an example of a linear complex
[Ag(NH3)2]+
Give an example of a tetrahedral complex
[CuCl4]2-
Give an example of a square planar complex
[Pt(NH3)2(Cl)2]
Give 2 examples of an octahedral complex
[Fe(H2O)6]2+
[Cr(NH3)6]3+
Why does the complex ion of Chloride ligands have a different shape to those of water ligands?
Chloride ions are too big to fit more than four around one ion
How does Cis-trans isomerism occur?
The complexes are locked into their current form
What does cis imply?
Trans?
“On the same side” - the same ligands are next to each other
“Opposite”- the same ligands are opposite (180 degrees from) each other
What is cis-platin used for?
Would trans-platin work?
As an anti-cancer drug
No
What are the possible side effects of cis-platin?
Hair loss
Fertility problems
Nausea
How do you minimise the side effects of cis-platin?
Use lowest dose possible
Target specific areas of the body
What general formula do complexes need for cis/trans isomerism to occur?
What would the B bond angles be for
a) cis
b) trans?
[M(A)4(B)2]
a) 90 degrees
b) 180 degrees
Define bidentate ligand
Forms 2 coordinate bonds with a transition metal ion
What must a ligand have to be able to be bidentate?
2 available lone pairs to form coordinate bonds
3 Ethyl diamine ligands form coordinate bonds with a metal ion. The complex ion has a coordinate number of 6. What is its shape?
Octahedral
Give 3 features of optical isomers
They have no plane of symmetry
They are non-superimposable mirror images of each other
They differ in the direction with which they rotate plane-polarised light
Which complex ions show optical isomerism?
Octahedral complexes formed from bidentate ligands
Define multidentate ligand
Forms 2 or more coordinate bonds to a transition metal ion from different atoms on the same ligand
Give the number of ligands, coordinate number, and shape of [M(EDTA)]2-
1 ligand
Coordinate number: 6
Shape: octahedral
On EDTA4- where are the lone pairs that form coordinate bonds?
On the single bond negative oxygens and Nitrogen’s
Why is EDTA most effective in alkaline conditions?
OH- reacts with H+
Equilibrium shifts to the right, ensuring EDTA can form 6 coordinate bonds
Give the general formula for a complex ion containing ethanedioate ions (M=2+)
Give the number of ligands and coordinate number
[M(C2O4)3]4-
3 ligands
Coordinate number: 6
Where are the lone pairs on the C2O4 2- ion?
On the negative single bond oxygens
Where are the lone pairs on ethyl diamine?
On the nitrogens
How does EDTA soften water?
By reacting with and removing Mg2+ and Ca2+ ions
What is EDTA used for in medicine?
To treat people with lead poisoning in a treatment called chelation therapy
How does chelation therapy work?
EDTA makes the toxic ions present in the body harmless
What is the molar ratio of metal:EDTA complexes
1:1
What kind of titration is EDTA used in?
What is usually in the burette?
Complexometric titrations, to calculate the concentration of metal positive ions in aqueous Solutions
EDTA
What is the chelate effect?
A multi-dentate ligand will always displace a uni-dentate ligand due to the increase in entropy
What colour is seen at the end of complexometric titrations?
What indicators are usually used?
The colour of the “free indicator”
Organic dyes, which show one colour as a ligand in a complex with a metal ion and another when not part of a complex
Why is oxygen not a very good ligand with haemoglobin?
They are weakly bonded so the oxygen can be readily given up to cells
Why is CO poisonous?
It can also bind to haemoglobin, preventing the transport of oxygen
What does a haem unit consist of?
How is haemoglobin formed?
A porphyrin ring coordinately bonded to Iron
When a haem is bonded to a globular protein
What is the coordination number of a porphyrin ring?
What does it consist of?
4
Fe coordinately bonded to 4 Nitrogen
Why does the chelate effect occur?
Mono-dentate are substituted by multi-dentate ligands to create a more stable complex
How can a more stable complex be formed?
A ligand substitution reaction
Explain why the entropy increases for the chelate effect
The number of moles increases
Disorder increases
Entropy change in positive
In a ligand substitution reaction why is 🔺H = 0?
Why is it feasible?
bonds broken and formed are equal
Mole number increases, so disorder increases, so enthalpy change is positive
Therefore T🔺S > 🔺H so 🔺G<0
Describe the practical method to fund the mass of a complex ion using titration
Filter solution
Wash solid with solvent/water to remove soluble impurities
Allow to dry in oven
Heat product to constant mass
In recrystallisation, why is a) a minimum volume of hot ethanol b) the solution is filtered hot c) cool the filtrate in ice to form crystals Important?
a) to form a saturated solution, which maximises yield
b) to remove INSOLUBLE impurities
c) remove soluble impurities
Why do transition metal ions give such different colours?
Partially filled d-sub levels
Electrons can shift up and down between unoccupied orbitals
This is called electron promotion
What is 🔺E?
Energy gap between orbitals
Explain why metal ions are coloured
d-orbitals split in energy levels
e- are promoted to higher energy d-orbitals by absorbing energy in the form of light
The colour transmitted and observed is the light not observed
What are the equations for 🔺E?
🔺E= hv
🔺E= hc/(wavelength)
What is h?
Planck’s constant
What is v?
Frequency of light absorbed
What is c?
Speed of light
How do you convert nanometers to metres?
What is the symbol for nanometers?
x10-9
nm
Units for frequency of light
s-1
Units for wavelength
m
Units for 🔺E
J
What 3 things can be done to change the 🔺E?
What do these changes result in?
Change the ligands bonded to the metal ion
Change the coordination number
Change the oxidation state of the metal ion
The complex to change colour
What should an absorbable vs concentration graph look like?
A straight line through the origin
A solution of KMnO4 has an unknown concentration
Describe briefly how colourimetry can be used to determine the concentration of this solution
Make samples of KMnO4 with known concentrations
Add ligand to make colour more intense
Find lambda max and set colourimeter to this wavelength
Plot a graph of conc./ moldm -3 (x-axis) vs absorbance (y)
Find absorbance of unknown on y, go across to line and find corresponding x coordinate
If you’re unsure how to do a calculation, what can you try to use?
The units
When testing for aldehydes, what uses transition metals’ variable oxidation states?
Fehling’s Solution
Cu2+ reduced to Cu+1(brick red colour) by an aldehyde
When testing for alcohols, what uses transition metals’ variable oxidation states?
Cr(+6) in acidified potassium dichromate is reduced to Cr(+3) by alcohols
What is a suitable reducing agent for vanadium (V)
Zinc and an acid (generally HCl)
How is the flask stoppered in the reduction of Vanadium (V)?
Why?
Why is bung not used?
With cotton wool
Allows Hydrogen to escape while preventing too much air from entering which would re-oxidise lower oxidation states of Vanadium
Would cause a build up of pressure
What colour is vanadium (+5)?
Yellow
What colour is vanadium (+4)?
Blue
What colour is vanadium (+3)?
Green
What colour is vanadium (+2)?
Purple
How do you re-oxidise vanadium’s Lower oxidation states?
With oxygen in air
OR
nitric acid
Why is nitric acid used to re-oxidise vanadium?
O2 takes too long
Why is the reduction of vanadium done in acidic conditions?
Why is there fixing during this experiment?
To provide H+ ions
Hydrogen is produced. Zinc reacts with an acid - metal+acid—-> salt + H2
What is the colour change is a redox reaction with MnO4- ?
What makes pink?
Why is an indicator not needed?
Colourless to pink
One extra drop of MnO4-
MnO4-‘s colour changes distinctly as it changes oxidation state
What is often used as an oxidising agent to analyse Fe2+ and C2O4 2-?
What is Fe2+ oxidised to?
What is C2O4 2- oxidised to?
Acidified MnO4-
Fe3+
CO2
What is the oxidation half equation for C2O4 2-?
C2O4 2- —-> CO2
What is the oxidation half equation for Fe2+?
Fe2+ ——> Fe3+
What is the reduction half equation for MnO4-?
What can you use this to form?
MnO4- —-> Mn2+
The full equation for the oxidation of C2O4 2- and the equation for the oxidation of Fe3+
What conditions does the MnO4- Solution need for a redox titration?
What do we use for this?
Acidified
Sulphuric acid
Why do we not use HCl to acidify a Solution of MnO4- ions?
emf MnO4-/Mn2+ > emf Cl2/Cl-
HCl contains Cl-
Therefore MnO4- reduced to Mn2+ and Cl- is oxidised to Cl2
This would give a larger titre value
What is the molar ratio of Fe2+:MnO4-?
5:1
What is the molar ratio of
C2O4 2-:MnO4-?
5:2
Why can transition metals be used as catalysts?
Their partially filled d-block orbitals mean they have variable oxidation states
What is a catalyst?
A substance that increases the rate of reaction but isn’t used up in the reaction
How does a catalyst work?
Provides an alternative reaction route with a lower Ea
How does a catalyst affect equilibrium?
No effect on position of equilibrium as it increases forwards and backward reactions equally
Only decreases time taken to reach equilibrium
What catalysts can be used in a catalytic converter?
What are they sprayed on and why?
Platinum, palladium, rhodium
A ceramic honeycomb structure to limit costs and maximise surface area
Define heterogeneous catalyst
Catalyst in a different state to the reactants (usually a solid) in
What are important examples of heterogeneous catalytic processes?
Haber
Contact process
How does a solid catalyst work?
3 marks
Reactants adsorbed onto active sites on catalyst surface
Reaction occurs with a lower Ea as bonds are weakened or new bonds are made on the surface
The products are desorbed
How do you maximise the efficiency of a solid catalyst?
Use a thin coating of it on a honeycomb structure to increase surface area
What catalyst is used in the Haber Process?
What is the reaction?
Fe(s)
N2(g) + H2(g) [equilibrium] 2NH3(g)
What does the contact process make?
SO3 which can be added to water to make Sulphuric acid
What is the catalyst in the Contact Process?
Vanadium (V) Oxide
V2O5(s)
What are the 2 steps for the contact process?
SO2(g) + V2O5(s) —> SO3(g) +V2O4(s)
V2O4(s) + 0.5O2(g) —> V2O5(s)
What is the overall equation for he Contact Process?
SO2(g)+0.5O2(g)—> SO3(g)
How is a catalyst poisoned?
Impurities adsorb strongly to the surface, blocking active sites.
This lowers the efficiency and can be extremely difficult to remove, ruining the catalyst which is v costly
How do you avoid catalyst poisoning
Purify reactants
Define homogenous catalyst
What does the reaction pathway often involve?
A catalyst that is the same phase as the reactants (usually taking place in a solution)
An intermediary
Give overall equation for I- and Peroxodisulfate
Don’t balance now, balance in exam
S2O8 2- + I- —> SO4 2- + I2
Give 2 steps for the catalysed reaction of I- and S2O8 2-
Don’t balance now, balance in exam
One: S2O8 2- + Fe2+ —-> SO4 2- + Fe3+
Two: Fe3+ + I- —-> Fe2+ + I2
What is autocatalysis?
When one product from a reaction is a catalyst for the reaction
How does the speed of reaction go for autocatalysis?
Starts slowly
Rate increases when catalyst is produced
Slows again when reactants run out
What is the equation for the oxidation of ethanedioate ions to CO2?
(Don’t balance now, balance in exam)
C2O4 2- —> CO2
What is the half equation for the reduction of MnO4-?
Don’t balance now, balance in exam
MnO4- —-> Mn2+
Why is the reaction of ethanedioic acid and MnO4- originally very slow?
This is an autocatalysis reaction. What is the catalyst?
It involves the reaction of 2 negative ions which repel is collision is difficult
Mn2+
What are the catalysed steps for C2O4 2- + MnO4-?
Don’t balance now, balance in exam
One: MnO4- + Mn2+ —-> Mn3+
Two: Mn3+ + C2O4 2- —-> Mn2+ +CO2
Why can Mn2+ act as a catalyst?
It has variable oxidation states of +2 and +3
Describe the autocatalysis concentration vs time graph
Slow rate in beginning as no catalyst is present
Then becomes steeper because it speeds up when catalyst is produced
Slows and eventually stops when reactants are used up
Why is the overall reaction for I- + S2O8 2- very slow?
How does a catalyst help?
Can both Fe2+ and Fe3+ be used as a catalyst? What does this mean?
Two negatively charged species are reacting together
This results in a high Ea as ions repel each other
Introduces a positive species
Yes: catalytic steps can happen in either order
Give examples of catalytic poisoning
Lead poisoning in catalytic converters in cars from leaded petrol, which can poison both Pt and Rh
Sulphur poisoning in Haber Process. H2 is obtained from natural gas and can be contaminated by sulphur which can poison the Fe (sulphur is added to natural gas to give it an odour to detect leaks)
Why do different complexes have different colours?
d orbital splitting is different
Light is absorbed for e- promotion
Different frequency of light absorbed for different complexes due to different 🔺E
Ratio of Fe2+: chromate ions
6:1
What is the shape of cisplatin
Square Planar
Name elements which are likely to form square planar complexes
Pt
Pd
Why can a Lewis acid also be a Bronsted Lowry acid
All donate H+ and H+ readily accept e-
Why are Fe3+ complexes more acidic than Fe2+
Fe3+ is a smaller ion with a higher charge
Therefore attracted to O in H2O more strongly, polarising H-O bond
This makes O-H bond weaker and more likely to break, releasing protons
Exam answer for “why are all aqueous solutions of Fe3+ more acidic than Fe2+”
Fe3+ is smaller with a higher charge
Fe3+ polarises O-H bond MORE THAN Fe2+, releasing more H+ ions
Is Al a transition metal
No
Metal 3+ with carbonate general equation
Salt + CO2 + H2O
Colour of copper aqua ion with carbonate
Blue green PPT
Which reacts with excess NaOH
Al
Which reacts with excess NH3
Cu
Give colours of V oxides from 5 to 2
5- yellow
4 - blue
3 - green
2 - purple
Colour of 5+ of V
Yellow
4+ V
Blue
+3 V
Green
2+ V
Purple
Which V oxide is purple
+2
What colour is a mixture of V +5 and +4
Green
Because blue and yellow are green
What is a suitable reducing agent for Vanadium
Zinc and an acid
Usually Zn and HCl
Method for colorimetry
Make solutions of know conc of same metal (some more some less conc)
Add ligand to intensify colour
Set spectrophotometer to lambda max
Measure absorbance
Plot graph of absorbance vs concentration (calibration curve)
Measure absorbance of unknown and determine its conc from curve
What is used in colorimetry?
Visible spectrophotometer or colorimeter
What is lambda max
The wavelength at which absorbance is at a maximum
