Transition Metals Flashcards
How do transition metals arise?
Incomplete d sub shell levels
What are the characteristics of a transition metal?
1) Complex formation
2) Formation of coloured ions
3) Variable oxidation states
4) Catalytic activity
Why is zinc not a transition metal?
It can only form a 2+ ion, which has a complete d sub shell
What is a complex?
Central metal ion surrounded by ligands
What is a ligand?
Atom / ion / molecule that can donate a lone electron pair
What is co-ordination number?
Number of co-ordinate bonds formed to a central metal ion
What is a monodentate ligand?
A ligand that can form one co-ordinate bond per ligand
Give 3 examples of a monodentate ligand
H2O
NH3
Cl-
What is a bidentate ligand?
One that has 2 atoms with lone pairs and can form 2 co-ordinate bonds per ligand
Give 2 examples of bidentate ligands
NH2CH2H2NH2
C2O4 2- –> (Ethanedioate ion)
Does the exchange of ligands NH3 and H2O change the co-ordination number and why?
No –> they are similar in size and uncharged
What is the reaction between a complex containing a Cu2+ ion and ammonia?
State the colour change
[Cu(H2O)6]2+ + 4NH3 –> [Cu(NH3)4(H2O)2]2+ + 4H2O
Blue solution –> deep blue solution
What is the reaction between [Cu(H2O)6]2+ and chloride ions?
State the colour change
[Cu(H2O)6]2+ +4Cl- –> [CuCl4]2- + 6H2O
Blue solution –> yellow/green solution
Reaction between [Co(H2O)6]2+ and chloride ions
State the colour change
[Co(H2O)6]2+ +4Cl- –> [CoCl4]2- + 6H2O
Pink –> blue solution
Reaction between [Fe(H2O)6]3+ and Cl-
State the colour change
[Fe(H2O)6]3+ + 4Cl- –> [FeCl4]- + 6H2O
Purple solution –> orange solution
Is solid copper chloride is dissolved in water, what product is formed?
[Cu(H2O)6]2+
Reaction between [Cu(H2O)6]2+ and NH2CH2CH2NH2
[Cu(H2O)6]2+ + 3NH2CH2CH2NH2 –> [Cu(NH2CH2CH2NH2)3]2+ + 6H2O
*This would be the same with ethanedioate ions
What is haem?
An iron(II) complex with a multidentate ligand
Reaction between [Cu(H2O)6]2+ and EDTA 4-
[Cu(H2O)6]2+ + EDTA 4- –> [Cu(EDTA)]2- + 6H2O
What is the chelate effect?
Substitution of monodentate ligand with a bidentate / multidentate ligand leads to a more stable complex
How can the chelate effect be explained?
Positive entropy (ΔS = positive)
More moles on product than reactants –> increased entropy –> more disorder
Uses of EDTA 4-
Add to rivers to remove poisonous heavy metal ions
In shampoos to remove calcium ions present in hard water
What are the shapes of complex ions?
1) Octahedral (with small ligands –> H2O / NH3)
2) Tetrahedral (with larger ligands –> Cl-)
3) Square planar
4) Linear
What type of isomerism do complexes show?
Cis-trans
Optical
What is cis-trans isomerism?
Cis –> atoms are arranged on the same side
Trans –> atoms arranged on different sides
What is optical isomerism?
Non-superimposable mirror image (cant match the original object when mirrored)
How are coloured ions formed?
Due to changes in :
1) Oxidation state
2) Co-ordination number
3) Ligand
What equations link colour, wavelength and frequency of light absorbed with energy difference between the split d orbitals
ΔE = hv OR ΔE = hc/λ
ΔE = energy difference between split orbitals (J)
h = plank’s constant (6.63 x 10^-34) (J s)
v = frequency of light absorbed (s^-1 or Hz)
c = speed of light (3.00 x 10^8) (m s^-1)
λ = wavelength of light absorbed (m)
What does changing the ligand / co-ordination number do to the d orbitals?
Alters the energy split between them, changing ΔE –> so changes the frequency of light absorbed
Which compounds don’t have colour and why?
Sc 3+ –> no d electrons to move around so no energy transfer equal to visible light
Zn2+ / Cu2+ –> full d shell so no space for e- to transfer –> no energy transfer equal to that of visible light
What is a spectrometer?
Contain a coloured filter to allow wavelengths of light through that would be most strongly absorbed by coloured solution
Method for spectrophotometry
1) Add appropriate ligand to intensify colour
2) Make up solutions to known concentration
3) Measure absorption or transmission
4) Plot graph of absorption vs concentration
5) Measure absorption or unknown and compare
What do compounds with high oxidation states tend to be?
Oxidising agents (gets reduced)
What do compounds with low oxidation states tend to be?
Reducing agents (gets oxidised)
What are the 4 oxidation states of vanadium?
State what colour their solutions would be
VO2 + –> +5 –> yellow solution
VO 2+ –> +4 –> blue solution
V 3+ –> +3 –> green solution
V 2+ –> +2 –> violet solution
Identify a reagent that can reduce a transition metal ion from a higher oxidation state to the lowest
Zinc
What metal ion complex is used in Tollens reagent and why?
[Ag(NH3)2]+ –> to distinguish between aldehydes and ketones
Why do you not need indicator for the titration between Fe2+ and MnO4 -?
The titration is self indicating as there is a significant colour change from reactant to product
Write the overall equation to change Mn(VII) to Mn (II)
MnO4- + 8H+ + 5Fe2+ –> Mn2+ + 4H2O + 5Fe3+
Write the steps for Mn(VII) being reduced to Mn(II)
1) MnO4- –> Mn2+
2) Add H+ and H2O
- MnO4- + 8H+ –> Mn2+ + 4H2O
3) Add e- to balance out the charge
- MnO4- + 8H+ + 5e- –> Mn2+ + 4H2O
4) Use Fe2+ as reducing agent
- Fe2+ –> Fe3+ + e-
5) Combine equations and remove e-
- MnO4- + 8H+ + Fe2+ –> Mn2+ + 4H2O + Fe3+
What is the only acid you should use for manganate titrations?
Dilute sulfuric acid
What happens if there isn’t enough acid for the manganate titration?
Why?
MnO2 is produced instead of Mn2+
Not acidic enough
Why is insufficient sulfuric acid an issue?
Brown MnO2 will mask the colour change and lead to larger volume of manganate being used for the titration
Why is HCl not used for manganate titrations?
Cl- ions would be oxidised to Cl2 by MnO4-, leading to a greater volume of manganate being used
Cl2 is poisonous
Why is nitric acid not suitable for manganate titrations?
Nitric acid is an oxidising agent, so oxidises Fe2+ to Fe3+
Leads to smaller volume of manganate being used
Overall equation for manganate titration with hydrogen peroxide
2MnO4- + 6H+ + 5H2O2 –> 5O2 + 2Mn2+ + 8H2O
Give the half equations for manganate titrations with hydrogen peroxide
Oxidation :
H2O2 –> O2 + 2H+ 2e-
Reduction :
MnO4- + 8H+ + 5e- –> Mn2+ + 4H2O
Write the half equations for the titration of manganate ions with ethanedioate
Oxidation:
MnO4- + 5e- + 8H+ –> Mn2+ + 4H2O
Reduction:
C2O4 2- –> 2CO2 + 2e-
Overall equation for the titration of manganate with ethanedioate
2MnO4- + 16H+ + 5C2O4 2- –> Mn2+ + 10CO2 + 8H2O
Overall equation between Fe2+ and C2O4 2- reacting with manganate together
3MnO4- + 24H+ + 5FeC2O4 –> 10CO2 + 3Mn2+ + 5Fe3+ + 12H2O
What doe catalysts do?
Increases their rate of reaction by providing an alternative reaction route / pathway with a lower activation energy
What types of catalysts do transition metals act as?
Heterogeneous
Homogeneous
What is a heterogeneous catalyst?
Catalyst –> substance which increases rate of reaction by providing an alternative reaction pathway with a lower activation energy
Heterogeneous –> the catalyst is a different phase from the reactants
What is a homogeneous catalyst?
Catalyst –> substance that increases rate of reaction by providing an alternative reaction pathway with lower activation energy
Homogeneous –> catalyst is the same phase as reactants
True or false: heterogeneous catalysts are usually gas and the reactants are usually solid
False
The catalyst is usually solid while the reactants are gaseous or in solution
Where does heterogeneous catalysis occur?
On the surface of the catalyst
Describe the steps in heterogeneous catalysis
1) Adsorption –> reactant molecules form temporary bonds to the metal surface
2) Reaction –> molecules bound to the catalyst metal surface react with each other
3) Desorption –> product molecules break their bonds with the metal surface and diffuse away
What is the problem is adsorption is too strong?
Products cant be released
What is the problem if adsorption is too weak?
Reactants don’t adsorb at a high enough concentration
What does the strength of adsorption indicate?
The effectiveness of the catalytic activity
Which 2 catalysts are the most useful?
Nickel
Platinum
How does surface area affect a catalyst?
Increased surface area of a soli catalyst improves its effectiveness
What is often used to maximise surface area? Why?
A support medium
Maximised surfaces area and minimises cost
Describe an example of a support medium
Rhodium on a ceramic support in catalytic convereters
What heterogeneous catalyst is used in the contact process?
V2O5
Write the steps in the contact process?
1) SO2 + V2O5 –> SO3 + V2O4
2) SO3 + 1/2 O2 –> V2O5
What is Cr2O3 catalyst used in?
Manufacture of methanol from carbon monoxide and hydrogen
Write the equation for the production of methanol
CO + 2H2 –> CH3OH
What process is Fe catalyst used in?
Haber process
Equation for haber process
N2 + 3H2 –> 2NH3
What is the poisoning of catalysts caused by and what does this lead to?
Impurities
Reduced efficiency
Give examples of catalytic poisoning
Poisoning by sulfur in haber process
Lead in catalytic converters of cars
What is homogeneous catalysis?
When the catalyst and reactants are the same phase, the reaction proceeds through an intermediate
Why is variable oxidation states important for homogeneous catalysis?
Intermediate has different oxidation state to original transition metal
Original oxidation state reoccurs at the end of the reaction
What is the reaction between iodide and persulfate catalysed by?
Fe 2+ ions
Overall equation for reaction between iodide and persulfate ions
S2O8 2- + 2I- –> 2SO4 2- + I2
Why is the uncatalysed reaction between iodide and persulfate ions slow?
1) Both ions are negatively charged
2) Causes repulsion between the 2 ions
3) High activation energy needed
What are the steps in the catalysed reaction between iodide and persulfate ions?
1) S2O8 2- + 2Fe2+ –> 2SO4 2- + 2Fe 3+
2) 2Fe 3+ + 2I- –> 2Fe 2+ + I2
In terms of electrode potentials, what allows a substance to act as a homogenous catalyst?
The catalysts electrode potential must lie between the electrode potentials of the 2 reactants
1) Reduces the reactants with more positive electrode
2) Then oxidises reactant with more negative electrode potential
Why is the catalysed reaction between iodide and persulfate ions quicker?
Involves collision between positive and negative ions in both stages –> has lower activation energies
What is autocatalysis?
Products of a reaction can catalyse the reaction
Which 2 ions does an autocatalysis reaction occur between?
Ethanedioate
Manganate
Overall equation for reaction of ethanedioate with manganate ions
2MnO4- + 5C2O4 2- + 16H+ –> 2Mn2+ + 8H2O + 10CO2
Steps in autocatalysis reaction between ethanedioate ions and manganate ions
1) 4Mn2+ + MnO4- + 8H+ –> 5Mn3+ + 4H2O
2) 2Mn3+ + C2O4 2- –> 2Mn2+ + 2CO2
What is the autocatalysis in the autocatalysis of ethanedioate and manganate ions?
Mn2+
What shape complexes does Ag form?
Linear
What colour are solutions containing silver?
Colourless
Reactions of halides with silver nitrate and the colour of the products
1) Ag+ + Cl- –> AgCl (White ppt)
2) Ag+ + Br- –> AgBr (Cream ppt)
3) Ag+ + I- –> AgI (Yellow ppt)
Reaction between silver chloride and dilute ammonia
AgCl (s) + 2NH3 (aq) –> [Ag(NH3)2]+ (aq) + Cl- (aq)
Reaction between silver bromide and concentrated ammonia
AgBr (s) + 2NH3 (aq) –> [Ag(NH3)2]+ (aq) + Br- (aq)
Why does silver iodide not react with ammonia?
It’s too insoluble
Where is [Ag(NH3)2]+ used?
In Tollen’s reagent
