tranisiton metals
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State the meaning of the term homogeneous.
Same phase
Suggest why ions from s block elements do not usually act as catalysts.
because they only have one oxidation state
A co-ordinate bond is formed when a transition metal ion reacts with a ligand. Explain how this co-ordinate bond is formed.
A central metal ion donates an electron pair to the ligand
Give one reason why, in the absence of a catalyst, the activation energy for the reaction between S2O82– ions and I– ions is high
both ions have a negative charge
In terms of bonding, explain the meaning of the term complex
transition metal surrounded by one or more ligands
State what is meant by the term co-ordinate bond.
A shared electron pair Both electrons from one atom
Brønsted–Lowry acid
H+ donor
Lewis acid
electron pair acceptor
State what is meant by the term bidentate ligand
Two atoms Each donating a lone electron pair
Suggest why the enthalpy change for the following reaction is close to zero.
same number and same type of bonds broken and made
State the origin of the colour of transition-metal complexes.
Electron transitions visible range
Give three changes to a transition-metal complex which result in a change in colour.
• ligands • oxidation states • co-ordination number
Outline a plan for experiments using this solution and this apparatus which would enable you to determine the concentration of iron(III) ions in a solution of unknown concentration.
• Add an appropriate ligand to intensify colour • Make up solutions of known concentration • Measure absorption • Plot graph of results • Measure absorption of unknown and compare
Ligand
an atom that can donate an electron pair
Co-ordination number
The number of co-ordinate bonds formed to a central metal ion
Explain the meaning of the chelate effect
When bidentate/multidentate ligands replace monodentate ligands Because there is an increase in entropy
Explain why some complexes containing transition metal ions are coloured
d orbitals have different energy Electrons move to higher orbitals Absorb white light Colour seen is that from complementary colours
Suggest why the oxidation state of chromium is zero in Cr(PF3)6
PF3 is neutral therefore Cr is neutral
Explain why the solution containing [Al(H2O)6]3+ is acidic.
Al3+ has a high charge and small size Al3+ has a high charge density
State why the concentration of aluminium sulfate solution can not be determined by colorimetry.
colourless solution
Explain why aqueous solutions containing [CuCl4]2– ions are yellow.
because of the light absorbed, yellow colour reflected
State the general property of transition metals that allows the vanadium in vanadium(V) oxide to act as a catalyst in the Contact Process.
variable oxidation states
Write two equations to show how vanadium(V) oxide acts as a catalyst in the Contact Process
V2O5 + SO2 → V2O4 + SO3 V2O4 + ½O2 → V2O5
Give one reason why impurities in the reactants can cause problems in processes that use heterogeneous catalysts
Impurities poison / deactivates the catalyst