Transition Metals Flashcards
Define transition metals
Elements that contain an incomplete d-subshell of electrons as either an atom or an ion
Properties of transition metals
Form complexes
These complexes tend to be coloured
Variable oxidation states
Can act as catalysts
Define ligand
Molecule/ion that forms a coordinate bond to a metal by donating a pair of electrons
Define Lewis base
Electron pair donator
Define Lewis acid
Electron pair acceptor
Define complex
Metal atom surrounded by ligands
Define coordination number
The number of coordinate bonds around a metal ion
How many coordinate bonds does copper normally have
6
What are the three types of ligand
Unidentate
Bidentate
Multidentate
Define unidentate
Forms 1 coordinate bond per molecule
Examples of unidentate ligands
NH3, H2O, Cl-, CN-
Define bidentate
Forms 2 coordinate bonds per molecule
Examples of bidentate ligands
1,2-diaminoethane, ethandioate ions
Define multidentate ligands
Forms multiple coordinate bonds per molecule
Examples of multidentate ligands
EDTA and polyphyrin
Which shape had the most ligand complexes
Octahedral
Which shape usually contains Cl- ligands
Tetrahedral
What metal ions are usually in square planar shapes
Pt2+ and Ni2+
What shape is cis-platin
Square planar
What shape are complexes with a Ag+ metal ion
Linear
Which type of ligands can have geometric isomerism
Unidentate ligands
Which type of ligand can display optical isomerism
Bidentate ligands
What changes the ease at which metals are oxidised
The pH of the solution and the nature of the ligands attached
What do Alkaline conditions cause in a ligand complex
Hydrolysis of the ligand
This results in a complex with an increasingly negative charge
This causes easier oxidation as the ion is negative
What does acidic conditions cause in a ligand complex
Prevents hydrolysis from taking place and the H+ ions provide electrons that reduce the complex ion
Is Zn an oxidising or reducing agent
Reducing
In a potassium manganite titration what properties must the acid have
Be strong, many H+
Not an oxidising agent (could react with the sample)
Not be a reducing agent (could react with MnO4- ions)
Why can’t you use HCl in potassium manganate titrations
oxidised to Cl- by MnO4
why can’t you use HNO3 in potassium manganate titrations
it is an oxidising agent
why can’t you use concentrated H2SO4 in potassium manganate titrations
it could be an oxidising agent
why does potassium manganate act as its own indicator
the pink colour intensifies due to an excess of Mn2+ once all of the Fe2+ have reacted
what is the colour change for a potassium dichromate titration
orange to blue/green
why is sodium diphenylaminesulphonate used in potassium dichromate titrations
to give a clearer end point, colourless to purple
steps for redox titration calculations
write the half equations for the oxidising agent and reducing agent
combine equations
calculate the number of mols of the oxidising agent (MnO4 or CrO7)
calculate the number of mols of reducing agents
calculate the number of mols in the original solution
determine the concentration of the original solution or percentage of reducing agent
the two commonly used oxidising agents when completing a redox titration with Fe2+
potassium dichromate and potassium manganate
the two equations which find number of mols
n=cv
mols=mass/Mr
define heterogeneous catalyst
a catalyst in a different phase from the reactants
define homogeneous catalyst
a catalyst in the same phase as the reactants
what makes a good catalyst
good adsorption or reactant molecules and the good desorption of products
how does adsorption of a reactant onto a metal surface speed up a reactant
weakening bonds within the reactant molecule, reducing the Eact
causing a reactant molecule to break up onto more reactant molecules, lowering the Eact
holding a reactant in a particular position, increasing the chance of a collision in a favourable position
giving a higher concentration of a reactant on the catalyst surface increasing the chance of a favourable collision with another reactant
how is a catalyst poisoned
the active sites are blocked
how does homogeneous catalysis proceed
via a catalyst
when does autocatalysis occur
when one of the products catalyses the reaction
what is the acidity of solutions of metal ions decided by
charge of the metal ion
size of the metal ion
why does charge of the metal ion affect pH
larger charge=greater dissociation=lower pH
why does size of the metal ion affect pH
greater ionic charge to size ratio = greater dissociation = lower pH
is the pH of a solution of M3+ ions or Mn2+ ions lower pH
Mn3+ ions
