Transition metals Flashcards
What are transition metals?
Metals that contain an incomplete 3D subshell
What 4 properties do transition metals have?
Form complexes
Form coloured ions
Have variable oxidation states
Act as catalysts
What is a ligand
Molecule or ion that forms coordinate bond with transition metal
What is a complex
Metal central atom or ion and its ligands
What is the coordinate number?
Number of coordinate bonds to the central metal atom or ion
What are monodentate ligands?
Ligands that form 1 coordinate bond
E.G H2O, NH3, Cl-
What are bidentate ligands + the 2 bidentate ligands we must know?
Ligands that form 2 dative covalent bonds
H2NCH2CH2NH2
1,2-diaminoethane
C2O4^2- –> Ethandioate
What are multidentate ligands + the 1 we need to know?
Forms multiple coordinate bonds per ligand
EDTA^4- Forms 6 coordinate bonds
What are the 4 ligand substitution reactions
Complete with no change in coordination number -
Complete with change in coordination number -
Incomplete with no change in coordination number -
The Chelate effect -
Write a complete ligand substitution with no change in coordination number using [Co(H2O)6]^3+
[Co(H2O)6]^3+ + 6NH3 –> [Co(NH3)6]^3+ + 6H2O
Write a complete ligand substitution with a change in coordination number using [Cu(H2O)6]^2+
[Cu(H2O)6]^2+ + 4Cl- –> [CuCl4]^2- + 6H2O
Write a incomplete ligand substitution with no change in coordination number using [Cu(H2O)6]^2+
[Cu(H2O)6]^2+ + 4NH3 –> [Cu(H2O)2(NH3)4]^2+ + 4H2O
Write the equation for the chelate effect using [Cu(H2O)6]^2+
[Cu(H2O)6]^2+ + 3C2O4^2- –> [Cu(C2O4)3]^4- + 6H2O
OR
[Cu(H2O)6]^2+ + EDTA^4- —> [Cu(EDTA)]^2- + 6H2O
What is the chelate effect and what is the enthalpy and entropy like and why?
Use the equation [Cu(H2O)6]^2+ + 3C2O4^2- –> [Cu(C2O4)3]^4- + 6H2O to help
Where multidentate ligands form thermodynamically stable complexes
Enthalpy is almost 0 as 6 Cu-O bonds formed and broken
Entropy is large as 7 species is produced from 4 species
Therefore, reaction is feasible with very low activation energy
What is the enthalpy of a complete ligand substitution with no coordinate number change like?
Small as bond energies of ligands are similar
Ligands must be a similar size for this substitution
When drawing a complex, how are the cis and trans complexes orientated?
Cis - X is found next to each other
Trans - X is found opposite each other
What transition metal complex do we need to know?
Cisplatin
What is the structure of cisplatin and its charge?
[Pt(NH3)2Cl2)
No overall charge
Why are some transition metal ions coloured? (edit these)
Some wavelengths of light are absorbed and the remaining are transmitted or reflected
Why are complexes formed from transition metals coloured?
It absorbs some wavelengths of light
Exciting electrons in the d orbital
Remaining wavelengths are reflected or transmitted.
What is the use of cisplatin?
Cancer therapy drug
What is the structure of cisplatin?
Square planar
Why is carbon monoxide toxic?
It forms a coordinate bond with Fe2+ in haem B, replacing oxygen
What equation is used to find the difference between resting state and excited state electrons?
E = hf = hc/λ,
E = energy (J)
h = plank constant = 6.63x10^-34
f = frequency (Hz)
λ = wavelength (m)
c = speed of light = 3x10^8 m/s
What factors affect the colour of an ion?
Change in oxidation state
Coordination number
Ligands
How can colourimetry be used to measure an unknown concentration of coloured ions?
Make a series of dilutions of a standard solution of know conc
Find absorbance using colorimeter
Plot graph of absorbance vs conc and add line of best fit
Find absorbance of unknown sample
Use graph to find conc
What oxidations states does vanadium exists in and what are the colours of these ions?
VO2+ = yellow
VO^2+ = blue
V^3+ = green
V2+ = purple
What can vanadium be reduced by?
Zinc metal
What can vanadium be oxidised by?
Common oxidising agents such as mangate (VII) solution (MnO4^-)
WHat factors affect redox potential for a transition metal ion
pH
Type of ligand
Conditions (temp, press, conc)
Redox titration of iron (II) and manganate (VII) equation + The colour change
5Fe^2+ + MnO4^- + 8H^+ –> Mn^2+ + 5Fe^3+ + 4H2O
Pink due to MnO4 being self indicating
Redox titration between ethanedioate and manganate (VII) + colour change and observations
5C2O4^2- + 2MnO4^- + 16H^+ –> 10CO2 + 8H2O + 2Mn^2+
Pink due to MnO4- being self indicating
Effervescence from CO2
Why can transition metals act as catalysts
They can form variable oxidation states and temporarily donate and accept electrons
How do catalysts speed up reactions?
Provide an alternative reaction pathway with a lower activation energy, therefore more particles have energy greater than Ea so more collisions cause a reaction.
What are heterogenous catalysts?
Catalysts that are in a different phase than the reactants.
How do heterogenous catalysts work?
Reaction occurs in active sites on the surface where vacant d orbitals can form weak bonds.
How must a heterogenous catalyst be suitable for a reaction?
Must be strong enough bonds to adsorb reactants but weak enough to de-adsborb
Write the contact process for the reaction of SO2 and 1/2O2 with a vanadium (V) catalyst
SO2 + 1/2O2 –> SO3
V2O5(s) + SO2(g) – > V2O4(s) + SO3(g)
V2O4(s) + 1/2O2(g) –> V2O5(s)
What is the contact process mechanism?
Via variable oxidation states of vanadium
Write the mechanism of the haber process
Reactants adsorb to active sites on the surface
Bonds in reactants weaken
New bonds form in products
Products de-adsorb from the surface
What reaction do we know uses the haber process + its catalyst
N2(g) + 3H2(g) –> 2NH3(g)
With Fe(s) catalyst
What is a homogenous catalyst?
Catalyst in the same phase as the reactants. Forms an intermediate species.
Reaction between Iodide ions and peroxodisulfate
S2O8^-2 + 2I^- —> 2SO4^2- + I2
Write equations showing how iron (II) acts as a catalyst in the reaction between peroxodisulfate and Iodide ions
S2O8^2- + 2Fe^2+ —> 2SO4^2- + 2Fe^3+
2Fe^3+ + 2I^- —> 2Fe^2+ + I2
What is catalyst poisoning?
Where impurities permanently adsorbs and blocks the active site
How can catalysts be used in a cost effective way?
Used as a fine powder sprayed across a wire mesh to increase SA and use less amount of expensive material
What is autocatalysis
A reaction where one of the products catalyses the reaction
Write how Mn2+ ions catalyse the reaction between manganite (VII) ions and ethandioate
5Mn^2+ + MnO4^- + 8H^+ —> 5Mn^3+ + Mn^2+ + 4H2O
2Mn^3+ + C2O4^2- —> 2Mn^2+ + 2CO2
How does a normal rate graph compare with a rate graph involving autocatalysis
Rate initially slower
Once product is catalyst and conc of product increases, catalyst increases so rate increases
What is the relationship between frequency of light and energy
Energy is directly proportional to frequency of light
Explain why, for example, a solution of copper II sulfate appears blue?
Absorbs all parts of the visible spectrum and reflect blue light
Explain why transition metals absorb light in the visible part of the spectrum with reference to electron transitions
d-subshell orbitals have a ground and excited state
Electrons absorb light with energy equivalent to visible light
Electrons promoted to excited state
Relax back and release thermal energy
Explain why different ligands, oxidation state and coordination number change the colour of a complex of the same metal
Variation of these factors changes the energy gap between ground and excited state d subshell orbitals
This causes a different frequency of light to be absorbed E = hf
