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
