UNIT 2 Section 4 - Transition Metals Flashcards
what is a transition metal
Transition metals are a d-block element that can from at least one stable ion with a partially filled d-subshell that form at least one stable ion
what is a ligand
Ligand is an atom/ion with a lone pair that forms a coordinate bond to the central metal ion
what is a complex
Complex metal ions with ligands co-ordinately bonded to it
what is the coordination number
the number of coordinate bonds in a complex
what are the properties of transition metals
- form coloured ions
- they form complexes
3.they show catalytic activity - exhibit variable oxidation states
give an example if an octehedral complex and draw it
colbalt bonded to NH3 with an overall 2+ charge
give an example of a complex with a tetrahedral shape and draw it
copper chloride or cisplatin
give an example of a linear shaped complex and draw it
silver ammonia
what is the equation for the total oxidation state of a metal
total oxidation state - total oxidation state of ligands
what is a unidentate ligand and give an example
a ligand that forms one coordination bond to the central metal atom
H2O
what is a bidentate ligand and give an example
a ligand that forms two coordinate bonds due to 2 lone pairs
NH2CH2CH2NH2
what is a multidentate ligand and give an example
a ligands that forms several coordinate bonds with a central metal ion
what type of isomerism is shown in octahedral complexes and when does it occur
optical isomerism
octahedral complexes with 3 bidentate ligands bonded to the central metal ion
what factors effects the energy gap in transition metals
- the identity of the metal
- the oxidation state of the metal
- identity of the ligands
- coordination number
how can you find an unknown concentration of a metal ion using colorimetry
- add specific ligands that intesifies colour
- pick a complementary filter colour
- measure the absorbance of the solution with known variety of concentrations and the unknowns
- produce a calibration curve with y as the absorbance and x as the concentration
- use absorbance of unknows to read the concentration of them on the graph
what is the redox potential
how easily the atom or ion is reduced to a lower oxidation state
what is the relationship between redox potentials and stability and reduction
the more positive a redox potential is the less stable the ion
the less stable the more likely the atom or ion is to be reduced
if a redox potential is negative what does this mean for oxidation
easier to oxidise negative species
what does amphoteric mean
that the precipitate that forms has properties allowing it to react with acids and bases
what do acidic conditions often do in redox reactions
in acidic conditions electrode potentials are more positive and the ions is more easily reduced
what do alkaline conditions often mean in redox reaction
in alkali conditions the electrode potentials are more negative and the ion is more easily oxidised
what reaction does tollens reagent use to identify aldehydes
what is the overall equation that occurs
Ag+ —–> Ag as a colourless solution of the complex ion [Ag(NH3)2]+ is formed
RCHO + 2[Ag(NH3)2]+ + 3OH- —–> RCOO- + 2Ag + 4NH3 + 2H2O
what is a catalyst
Catalyst are substances that speeds up reaction without being used as it provides an alternative mechanism with lower activation energy and it doesn’t effect equilibrium constant
why do transition metals work as catalysts
Transition metals work because the metal varies its oxidation state
what is a heterogenous catalyst
a catalyst in a different state to the reactants
what are the risks of using heterogenous catalysts and give two example
There are risks like poisoning as some substances can block the active sites and ruin their function
sulfur blocks iron in the haber process
lead blocks platinum in catalytic converters
how does a heterogenous catalyst work
- Reactants absorbed onto surface of the active site which weakens the bonds and bring molecules closer in a more favourable orientation
- Reaction occurs
- Products are desorbed
what are the equations of the contact process to make H2SO4
- V2O5 + SO2 —-> V2O4 + SO3
- V2)4 + 1/2O2 —-> V2O5
the SO3 from the first equation goes on to react with water to produce H2SO4 and the V2O5 is recreated
what is a homogeneous catalyst
a catalyst in the same state to the reactants
what state are homogeneous catalyst usually in and give an example
solution
acid catalysed esterification
how do homogeneous catalysts work
- Catalyst reacts with one of the reactants to form an intermediate
- Intermediate then reacts with one of the reactants to form product faster than the original reactant would of
give the equations of iodine ions reacting with S2O82- catalysed by a homogeneous catalyst
- 2Fe2+ + S2O82- ——> 2Fe3+ + 2SO4-
- 2Fe3+ + 2I- —-> 2Fe2+ + I2
what colour is vanadium in the oxidation state of 5,4,3,2,
5 = yellow
4= blue
3= green
2= violet
what is the reducing agent used for vanadium and what is important in the reaction and why
Zinc
zinc powder cant be transferred to prevent further reactions
what is the oxidising agent for vanadium
potassium manganate
what is a ligand substitution reaction
when one ligand is replaced by another ligand
what is the chelate effect
when monodentate ligands are substituted by bi or multi dentate ligands to form a much more stable complex as they form more coordinate bonds
why is the reaction feasible in ligand substitution reactions
due to the entropy increasing and the enthalpy change being very little due to the same number and type of bonds being formed or broken similar in energy
when do we use the chelate effect in medicine
to prevent the poisoning of metal ions using EDTA
what are the physical properties of transition metals
- they all have a high density
- they all have high MP and BP
what are the two types of isomerism complexes can show
optical isomerism and CIS-TRANS isomerism
what type of complexes does CIS- TRANS isomerism occur and give examples
square planar complexes
octahedral complexes with four ligands of one type of 2 of another
how does oxygen get transported around the body by haemoglobin
In the body both water and oxygen will bond to the Fe2+ ions as ligands so the complex can transport oxygen when needed.
When there is a high concentration of oxygen in the lungs the oxygen molecules substitute the water ligands to form oxyhaemoglobin which is then carried in the bloodstream.
When the oxyhaemoglobin gets to a place where oxygen is needed the oxygen molecules are substituted for water molecules where us can then return to the lungs
how does carbon monoxide poisoning happen and what are the consequences
Carbon monoxide poisoning: the carbon monoxide ligands substitute the water ligands and forms a very strong bond with the Fe2+ ion
This means it can no longer readily exchange with oxygen and this stops the haemoglobin from being able to transport oxygen around the body.
The consequences of this is the organs are then starved of oxygen and this can cause headaches, dizziness, unconsciousness and even death
what is the equation for the energy gap
deltaH= hv = hclambda
what are the uses of iron
vehicle bodies
reinforce concrete
what are the uses of titanium
jet engine parts
what are the uses of copper
water pipes
which electrons do transition metals lose first when forming ions
4s
give 4 examples of common monodentate ligands
cl-
H2O
NH3
CN-
draw ethanedioate and how many coordinate bonds can if form to a transition metal ion
2 coordinate bonds
coo- — coo-
draw benzene-1,2-diol
how many coordinate bonds can it form
benzene bonded to OH on neighbouring carbons
2 coordinate bonds
draw ethan-1,2-diamine
how many coordinate bonds can it form
NH2–CH2—CH2—NH2
how many coordinate bonds does EDTA4- form
6
explain the chelate effect in terms of entropy and the reaction that is occuring
the number of molecules increases when multidentate ligands displace ligands with fewer coordinate bonds per molecule
this increases entropy and that makes gibbs free energy more negative making the reaction feasible
a more stable complex ions is formed
if a transition metal ion has 4 ligands what shape is it usually
tetrahedral
name the exception to the general rule the ions with 4 ligands is generally tetrahedral
platin forms square planar like in cisplatin
what shapes of ions do cis-trans isomerism occur in
square planar and octehedral
what happens to the coordination number when Cl- ligands replace NH3 or H2O as liagands
decreases as the Cl- ionic radius is much larger
what is haem- its metal ion, coordination number and ligands
molecule made up of protein chains
Fe2+ as a central metal ion
coordination number of 6
4 ligands are porphyrin and 1 is nitrogen and one is oxygen
what colour is the Fe2+ aqua ion
green
what colour is the Fe3+ aqua ion
pale brown
what colour is Cr2+ aqua ion
blue
what colour is Cr3+ aqua ion
red/violet
what colour is CO2+ aqua ion
brown
what colour is Co3+ aqua ion
yellow
why can transition metals have variable oxidation states
they have partially filled d-orbitals so can lose 4s and 3d electrons
what oxidation state to all metals apart from Sc have and why
all have +2 due to loss of electrons from the 4s orbital
when oxidation states are high do the transition metals exist as simple ions
no after +3 oxidation state the metal ions covalently bond to other species
what is the use of the complex [Ag(NH3)2]+ ion
used in tollens reagent to test for aldehydes and ketones where solver mirror formed with aldehyde
what colour us MnO4-
deep purple
what colour is Mn2+
pink
write the half equation for the reduction of MnO4- to Mn2+
MnO4- + 8H+ + 5e- —-> Mn2+ + 4H2O
why are redox titrations with transition metals said to be self indicating
they usually involve a solour change as the metal is changing oxidation state
what colour is Cr2O72-
orange
what colour is Cr3+
green
write the half equation for the reduction of Cr2O72- to Cr3+
CrO72- + 14H+ + 6e- —> 2Cr3+ + 7H2O
what happens to aqua metal ions in acidic conditions
they get reduced
what happens to aqua metal ions in alkaline conditions
they get oxidised
what happens to aqua metal ions is neutral conditions
no change
why are transition metals good catalysts
they can exist in variable oxidation states so can provide alternative pathways easily
what is an advantage of using a heterogeneous catalyst
no need for seperation of products from catalyst
what properties does the catalyst need to have to make it a good catalyst
cant absorb too strongly otherwise the products wont desorb
cant adsorb too weakly or the reactant would not be held in place for long enough for bonds to be weakened
how can you increase the efficiency of heterogeneous catalyst
increase the SA to increase the number of active sites present
spread onto honeycomb medium
what is the haber process form and what catalyst is used
makes ammonia and the catalyst used is iron
what is the equation that happens in the haber process
N2(g) + 3H2 (g) —–> 2NH3
what size/shape is the catalyst for the Haber process
pea sized lumps to increase SA
what is the haber process poisoned by
sulfur impurities in gas streams
define the term autocatalysis
when a product of a reaction is also a catalyst for that reaction
write a half equation for the conversion of C2O42- ions into CO2
C2O42- —–> 2CO2 + 2e-
