Flashcards in Transition Metals Deck (49):
What is a ligand
An atom, ion or molecule which can donate a lone pair of electron.
Define coordinate bonding
It is when the shared pair of electrons in the covalent bond come from only one of the bonding atoms
What is coordination number
The number of coordinate bonds formed to a central metal ion
Give examples of monodentate, bidentate and multidentate ligand
Monodentate : Cl-, H2O, NH3
Bidentate : NH2CH2CH2NH2 and C2O4^2- (ethanedioate ion)
Multidentate : EDTA^4- can form 6bonds
Give equation of incomplete substitution reaction between copper and ammonia, then state the colour change
[Cu(h2o)6]^2+ + 4NH3 -> [Cu(Nh3)4(h2o)2]^2+ + 4H2o
From pale blue to deep blue solution
Why would there be a change in coordination number when Cl ligand is involved
Cl- is a larger ligand than the uncharged h2o and nh3
When [Cu(h2o)6]^2+ is reacted with Cl ligand, what forms and state the colour change
If solid copper chloride (or any other metal) is dissolved in water, what does it form?
Aqueous [Cu(h2o)6]^2+ complex forms
NOT the CuCl4 complex!!!
Colour of [CoCl4]^2-
When would partial substitution of ethanedioate ions occur
When dilute aq solution containing c2o4^2- ions are added to a solution containing aq Cu2+
4 h2o will be replaced
Give an example of an iron(ii) complex with a multidentate ligand
How does Fe(ii) in haemoglobin work in the body
In the body both H2O and O2 bind to Fe2+ ions as ligands, so the complex can transport O2 two where it’s needed then swap to h2o molecule.
In lungs where O2 concentration is high, water ligands are substituted for O2 molecules to form oxyhaemoglobin which is carried around body in blood
How can CO harm human in terms of haemo
What are the impacts on the human
CO is toxic to humans as it can form a strong coordinate bond with haemoglobin.
This is a stronger bond than that made with oxygen and so it replaces the oxygen attaching to the haemoglobin
impact - cause dizziness, headaches, even death
Chemical properties of transition metals, name 4 and what is it caused by
Form complex ions
Various oxidation states
Form coloured compounds
These are caused by presence of an incomplete d sub shell
Physical properties of transition metals and question why
Good electricity conductor
High melting and boiling point
- due to metallic bonds formed, electrostatic force of attraction between positive ions and sea of delocalised electrons
In period 4, which 2 are not transition metals, and why
Sc and Zn
Sc is 3d1 4s2, it must form Sc3+ ions so there would be no electrons in the d she’ll.
Zn is 3d10 4s2, when it forms Zn2+, there would be a full d she’ll
Why is electronic configuration of
Cr: [Ar] 3d54s1 and
Cu: [Ar] 3d10 4s1
For Cr, it prefers one electron in all 3d sub shell, making it more stable
For Cu, it prefers a full 3d sub shell, making it more stable as well
What is the chelate effect
The substitution of monodentate ligand with a bidentate or multidentate ligand leads to a more stable complex
Redox potentials tell you how easily it is reduced to a lower oxidation state. The more positive it is the more/less stable is it and the more or less likely will it be reduced
The more positive, the less stable, and the more likely it will be reduced
What 2 factors affect redox potentials in transition metal chemistry
Ligands (depends on how well they bind to the metal ion)
Formation of coloured ions is associated with incomplete d orbital, what are the 3 things that cause colour changes to arise from?
Colour of [Co(NH3)6]2+
Colour of [Co(NH3)6]3+
Colour of change of Co(H2o)6^2+ + 4Cl- -> [CoCl4]2-
Pink to blue
How colour arises
Colour arises from electronic transitions from the ground state to excited states : between d orbitals
A portion of visible light is absorbed to promote d electors to higher energy levels. The light that is not absorbed is transmitted to give the colour we see.
Give the equation that links the frequency of light absorbed with energy difference between the split d orbitals.
Difference in Energy =hv
H=plancks constant (J)
V=frequency of light absorbed (Hz/s^-1)
The colour absorbed and the colour we see is demonstrated by the relationship of complementary colours what method could you use to find out
Draw a circle with 6 fractions - write red orange yellow green blue green
What would alter the energy split between d orbitals and thus changing frequency of light absorbed
Changing a ligand or coordination number
Why does scandium not have a colour
It’s ion is Sc3+, it hasn’t got any d electrons to move around, so there’s no energy transfer
Why’s ther no colour in Zn2+ and Cu+
They have full d shells, no space for electrons to transfer
What’s a spectrometer and what does it do?
It is used to determine the concentration of solution by measuring how much light it absorbed.
It contains a coloured filter. The colour of filter is chosen to allow wavelengths of light through that to be most strongly absorbed by the coloured solution. ( more concentrated solutions absorb more light )
If complexes have pale Colour and we’re unable to investigate through spectrometer, what can we do?
Add a suitable ligand to intensify the colour
Vanadium has 4 main oxidation states, what are they and what are their colours.
Adding what would reduce vanadium down through each states?
V 5+ Yellow
V 4+ Blue
V 3+ Green
V 2+ Violet
Colour of MnO4- and Mn2+
Which acid must be used for manganate titrations, why can’t it be other acids
Dilute H2SO4 Must be used
Using a weak acid like ethanoic acid would not be able to supply the large amount of H+ ions needed
Can’t be conc Hcl as Cl- ions will be oxidised to cl2
Can’t be nitric acid as it is an oxidising agent and would oxidise Fe2+ to Fe3+
See chemrevise notes for details
What is a heterogenous catalyst
It is in a different phase from reactants
Catalyst usually solid
What is a homogenous catalyst
It is in the same phase as reactants, the reaction proceeds through an intermediate species
How would strength of adsorption help determine effectiveness of catalyst?
Give 2 catalysts that are most useful in this sense
Some metals like W have too strong adsorption and so products cannot be released.
Metals like Ag have too weak adsorption so reactants do not adsorb in high enough concentration
Nickel and platinum have right strengths
What’s the active site
The place where reactants adsorb (gather) on to the surface of the catalyst
An example of heterogenous catalyst is in the contact process, which catalyst is used
What catalyst is used in Haber process
Why can’t leaded petrol used in cars fitted with a catalytic converter
Lead strongly adsorbs (to gather) onto the surface of the catalyst
Silver can form complexes and show catalytic behaviour, Why is it different from transition metals
It doesn’t form coloured compounds and does not have variable oxidation state.
Also doesn’t have incomplete d she’ll
State the equation and colour change in the reaction between NaOH and Cr3+
Cr3+ -> Cr(OH)3 green ppt 🌳
Dissolved in excess to form [Cr(OH)6]3- dark green solution
What is disproportionate
It is when the same element has been oxidised and reduced in the same reaction
Colour of copper
Colour of CuSo4
What does amphoteric metals mean
Give an example
They can act as both acid and base