Transition metals Flashcards
What is a transition metal
A d- block element that can form at least one stable ion with an incomplete d-subshell, or exists as an atom which has an incomplete d-subshell
Why do Cr and Cu have electron configurations (Ar)3d5,4s1 and (Ar)3d10,4s1 respectively
An e- from the 4s orbital moving into the 3d orbital to create a more stable half full or full 3d subshell
Why is Zn not a transition metal
Forms only 1 stable ion: Zn2+ which has a full-subshell
Give 4 properties of transition metals
Variable oxidation states
Coloured ions in solution
Good catalysts
Complex formation
Why do transition metals have variable oxidation states
Electrons sit in the 4s and 3d subshells which are very close, therefore electrons are gained and lost using a similar amount of energy when they form ions
What is the Pneumonic to remember the colours of vanadium
You (VO₂⁺)
Better (VO²⁺)
Get (V³⁺)
Vanadium (V²⁺)
What colour is VO₂⁺(aq)
Yellow
What colour is VO²⁺(aq)
Blue
What colour is V³⁺(aq)
Green
What colour is V²⁺ (aq)
Violet
What colour is Cr³⁺(aq)
Green/Violet
When is Cr³⁺(aq) violet
When surrounded by water ligands, however commonly substituted with other molecules and so usually green
What colour is Cr₂O₇⁻(aq)
Orange
What colour is Mn²⁺(aq)
Pale pink
What colour is MnO₄⁻(aq)
Purple
What colour is Fe²⁺(aq)
Pale green
What colour is Fe³⁺(aq)
Orange (rust)
What colour is CO²⁺(aq)
Pink
What colour is Ni²⁺(aq)
Green
What colour is Cu²⁺(aq)
Blue
What colour are Zn²⁺(aq) and Sc³⁺(aq)
Colourless
What is a complex ion
A central transition metal ion is surrounded by ligands bonded by dative covalent bonds
What is a ligand
A molecule/ion that forms a covalent bond with a central metal atom by donating a pair of e-
What is a monodentate ligand
Ligands which only donate 1 pair of e- (to a transition metal ion) from one atom on the molecule/ion, forming 1 coordinate bond
Give 3 examples of monodentate ligands
:H2O
:NH3
:Cl-
What is a bidentate ligand
Ligands which donate 2 pairs of e- (to a transition metal ion) from 2 atoms on the molecule/ion, forming 2 coordinate bonds
Draw the structure of ethanedioate
Draw the structure of
Ethane-1,2-diamine
What is a multidentate ligand
Ligands which donate 2 or more pairs of e- (to a transition metal ion) from 2 or more atoms on the molecule/ion, forming 2 or more coordinate bonds
Give 2 examples of Multidentate ligands
EDTA⁴⁻
Haem
How many coordinate bonds does EDTA⁴⁻ form
6
How many coordinate bonds does Haem form
4
What is the shape of a complex dependent on
The size of ligands bonded
Coordination number
What is a coordination number
The number of coordinate bonds in a complex (Not number of ligands)
How many :NH3 and H2O: ligands can fit around a central metal ion
6
How many Cl- ligands can fit around a central metal ion
4
Give an example of 2 ligands where only 3 of them can fit around a central metal ion
Ethanedioate
Ethane-1,2-diamine
What shape do complexes with a coordination number of 6 form
Octahedral
What is bond angle in an octahedral structure
All angles 90 degrees
What shape do complexes with a coordination number of 4 form
Tetrahedral and square planar shapes
Draw the structure of cis-platin
What is cis-platin
An anti cancer drug
What is the bond angle in a tetrahedral structure
109.5 degrees
What is the bond angle in a square planar structure
90 degrees
How does cis platin work
Kills cancer by preventing cell division
What is a risk with cis-platin
Also kills healthy cells
How are risks associated with cis-platin minimised
By using small amounts/in short bursts
What shape do complexes with a coordination number of 2 form
Linear shape
Give an example of a complex with a linear shape
Tollens reagent
Draw the structure of tollens reagent
What is the bond angle in a linear complex
180 degrees
What is tollens reagent used for
To distinguish between aldehydes and ketones
How do we calculate the oxidation state of the central metal ion in a complex
Oxidation state of metal = Total oxidation state (complex charge) - total oxidation state of ligands
What shape is haemoglobin
Octahedral
State where each of the coordinate bonds in haemoglobin come from
4 Nitrogen from one multidentate ligand: Haem
1 From globin protein
1 from either oxygen/water molecule
Explain how haemoglobin transports oxygen around the body
Oxygen substitutes water ligand in the lungs (where there is a high (O2) ) forming oxyhaemoglobin
This then gives up oxygen to organs and is substituted by water formed from respiration in muscle cells
What is CO
Carbon monoxide
A poisonous gas that causes headaches, unconsciousness and death
What colour is CO
Colourless and odourless
What happens when CO is inhaled
CO replaces the H2O/O2 ligand on haemoglobin
Why is CO dangerous when bonded to haemoglobin
It bonds strongly
Therefore not readily replaced by O2/H2O and so O2 cant be transported which leads to oxygen starvation
Why is CO not readily replaced by H2O/O2 in haemoglobin
CO has 210 times greater affinity to haemoglobin than oxygen
What does CO poisoning lead to
Oxygen starvation
What is the condition for a complex to display optical isomerism
When complexes are non-superimposable mirror images
What is the most likely case for optical isomerism
In octahedral complexes with 3 bidentate ligands
What is the most likely case for Cis-Trans isomerism
Octahedral complexes with 4 ligands of the same type and 2 ligands of a different type
Square planar complexes with 2 ligands of the same type and 2 ligands of a different type
When do we see Trans isomers
When the 2 ligands of the same type which are opposite each other
When do we see Cis isomers
When the 2 ligands of the same type which are adjacent to each other
Give an example of a molecule which displays Cis-Trans isomerism
Cis-Trans platin
What is the difference between cis-trans platin
Cis-Platin is an anti cancer drug
Trans-Platin is not
When does d-subshell splitting of a metal ion occur
D subshell is split into 2 when ligands bond with the central metal ion
Why do we get d-subshell splitting of a metal ion when ligands bond
Some orbitals gain energy and therefore an energy gap is created
What is the ground state of electrons
The state electrons are in when ligands are attached (without light the input of light energy)
How can electrons move from the ground state to an excited state
By absorbing light energy
What is the an excited state of electrons
The state electrons are in when ligands are attached after the absorbance of light energy
What is the must exist about relationship between light energy and ∆E in order for an electron to be excited
Energy from light energy must equal ∆E in order for an electron to be excited
What does ∆E correspond to when an electron is excited
∆E will correspond to one of the wavelengths of light
Why cant Sc go from the ground state to an excited state
Sc ions have empty d-subshells
Why cant Zn go from the ground state to an excited state
Zn ions have full d-subshells
What 3 things is the magnitude of ∆E dependent on
Central metal ion and its oxidation state
Type of ligand bonded
Coordination number
What is the equation for calculating energy absorbed by electrons from the ground state to an excited state
∆E = hv = hc/λ
What does ∆E represent in the equation ∆E = hv = hc/λ and what is its units
Change in energy
(J)
What does h represent in the equation ∆E = hv = hc/λ
Planck’s constant
What does v represent in the equation ∆E = hv = hc/λ and what is its units
Frequency of light absorbed
(Hz)
What does c represent in the equation ∆E = hv = hc/λ
Speed of light
What does λ represent in the equation ∆E = hv = hc/λ and what is its units
Wavelength of light absorbed
(m)
What does the frequency of light absorbed by transition metal complexes depend on
The size of ∆E
When white light hits a transition metal solution, only 1 frequency is absorbed. Write the colours of visible light in order of increasing frequency
R O Y G B I V
–Increasing frequency—>
What does a larger ∆E mean about the frequency of light absorbed by e-
Larger ∆E means a higher frequency of light is absorbed
What happens to frequencies of light which aren’t absorbed by an e- when excited
Either reflected transmitted
What creates a complementary colour (the colour we see observe metal complexes)
A combination of the frequencies of visible light which are reflected or transmitted when an e- is excited
What does a colour of a complex ion depend on
The size of ∆E
Coordination number
Change of ligand
Give the equation for a ligand substitution where coordination number and shape stay the same. State the colour and shape of the complex in reactants and products
(Co(H2O)6)²⁺(aq) + 6NH3(aq) –> (Co(NH3)6)²⁺(aq) + 6H2O(l)
(Co(H2O)6)²⁺(aq) - Pink, Octahedral
(Co(NH3)6)²⁺(aq) - Straw, Octahedral
Give the equation for a ligand substitution where both coordination number and shape change. State the colour and shape of the complex in reactants and products (Cu)
(Cu(H2O)6)²⁺(aq) + 4Cl-(aq) —> (Cu(Cl4))²⁻(aq) + 6H2O(l)
(Cu(H2O)6)²⁺(aq) - Pale blue, Octahedral
(Cu(Cl4))²⁻(aq) - Yellow, Tetrahedral
When is ligand substitution where both coordination number and shape change most likely
When a smaller ligand is substituted by a larger ligand
Give the equation for a reaction where oxidation state changes, but coordination number and shape stay the same. State the colour and shape of the complex in reactants and products
(Fe(H2O)6)²⁺(aq) —> (Fe(H2O)6)³⁺(aq)
(Fe(H2O)6)²⁺(aq) - Pale green - Octahedral
(Fe(H2O)6)³⁺(aq) - Yellow - Octahedral
What does a colorimeter measure
Absorbance of light by a coloured sample
Draw the colour wheel which we use to predict colour of of light absorbed
Starting at 12 o’clock going clockwise: Red, Yellow, Green, Pale blue, Dark blue, Magenta
State the 5 steps in measuring the concentration of transition metal ions in solution using colorimetry
1 - Set colourimeter to zero
2 - White light is filtered into a narrow range of frequencies producing monochromatic light
3- Monochromatic light passes through a sample held in a cuvette (some light is absorbed)
4 - Light which isn’t absorbed travels to the detector
5 - Draw a calibration graph by making up known concentration of metal solution and plot measured absorbance ( Then draw line of best fit)
How do we set a colorimeter to zero
Measure absorbance of a blank sample (H2O)
What colour must the colour produced from the filter be the same as in using colourimetry to measure the concentration of transition metal ions in solution
The colour absorbed by the metal ion in solution
What does a detector do in colourimetry
Measures the level of absorbance against the blank sample
What are 3 advantages of using colourimetry to measure the concentration of transition metal ions in solution
Quick
Cheap
Non - destructive
What are the 2 conditions required to use colourimetry to measure the concentration of transition metal ions in solution
Reactant for which the concentration is being measured must be coloured
All other reactants and products aren’t coloured
What are 2 disadvantages of using colourimetry to measure the concentration of transition metal ions in solution
Can’t analyse colourless substances
Errors from similar colours
When can a colour change of a transition metal ion complex occur
When there is an exchange/substitution of ligands
Write the equation for the reaction of (Co(H2O)6)²⁺(aq) with excess NH3(aq). State the shape and colour of reactant and product complexes
Write the equation for the reaction of (Cu(H2O)6)²⁺(aq) with excess NH3(aq). State the shape and colour of reactant and product complexes
Partial substitution
Give an example of 2 monodentate ligands of a similar size
H2O
NH3
How many Cl- ligands can fit in a transition metal complex
4
Write the equation for the reaction of (Co(H2O)6)²⁺(aq) with Cl-(aq). State the shape and colour of reactant and product complexes
Write the equation for the reaction of (Cu(H2O)6)²⁺(aq) with Cl-(aq). State the shape and colour of reactant and product complexes
Write the equation for the reaction of (Fe(H2O)6)³⁺(aq) with Cl-(aq). State the shape and colour of reactant and product complexes
Which type of ligands form stronger bonds and therefore more stable complexes in a metal ion complex:
Monodentate
Bidentate
Multidentate
Multidentate ligands form stronger bonds and therefore complexes that are stronger
What is the chelate effect
A substitution of a monodentate ligand by a bi/multidentate ligand leading to an increase in entropy and therefore stability of a complex
Explain how ligand substitution from a monodentate ligand to a multidentate ligand displays the chelate effect
Creates a solution with more particles and therefore an increase in entropy and stability
What does a reaction with increasing entropy mean about the ease of reversibility of the reaction
Difficult to reverse since the reverse reaction would have a decrease in entropy, and delta H is often small as energy breaking/making is similar, therefore reaction not feasible
What 2 things are required to reduce VO₂⁺ to V²⁺
Zinc
Acidic solution
Write the redox equation for the reduction of VO₂⁺ to VO²⁺
Write the redox equation for the reduction of VO²⁺ to V³⁺
Write the redox equation for the reduction of V³⁺ to V²⁺
How many steps does it take to reduce VO₂⁺ to V²⁺
3
What do redox potentials tell us
How easily an ion is reduced
Explain the relationship between the stability of an ion and its redox potential
The least stable ions have the largest redox potential and are more likely to be reduced
Why might difference in redox potential values in the data book be different to the values obtained in an experiment
Alterations in standard conditions
Type of ligand bonded
pH
Give 2 factors which affect redox potential values
Type of ligand bonded
pH
Explain how the type of ligand bonded to a metal ion affects its E°
E° always measured in aqueous solution (metal ion surrounded by H2O ligands)
So E° can be higher or lower than standard value if other ligands are bonded which may form stronger or weaker bonds affecting E°
Explain how pH affects E° of a transition metal ion
The more acidic (lower pH) the larger the E° and therefore the ion is more easily reduced
What is tollens used for
To distinguish between aldehydes and ketones
Ag+(aq) + e- ⇌ Ag(s) E°= +0.80V
What does this mean about how easily Ag+ is reduced
Ag+ is easily reduced to Ag
How is tollens reagent made
By reacting enough NH3(aq) to aqueous silver nitrate
What is the formula for tollens reagent
(Ag(NH3)2)+
What colour is tollens reagent
Colourless
What happens when we add tollens reagent to an aldehyde
Ag+ reduced to Ag(s) (silver mirror)
Aldehyde is oxidised to a carboxylic acid
What is the general redox equation for when we add tollens reagent to an aldehyde
RCHO(aq) + 2(Ag(NH3)2)+(aq) + 3OH-(aq) –> RCOO-(aq) + 2Ag(s) + 4NH3(aq) + 2H2O(l)
Can ketones be oxidised by tollens reagent
No
What can we do to find the concentration of a reducing agent (Fe2+/C2O42-)
Titrate against an oxidising agent (MnO4-)
What are the 5 steps in finding the concentration of (Fe2+/C2O42-) in a redox titration - state colour changes for each
1- Place reducing agent (Fe2+/C2O42-) in a conical flask (unknown conc & vol) and add excess H2SO4
2- Place oxidising agent MnO4- in burette (known conc)
3 - Add MnO4- to conical flask until faint colour of MnO4- disappears (drop by drop near end point) - Purple to colourless for Fe2+/Colourless to light pink for C2O4-)
4- Read from bottom of meniscus at eye level how much MnO4- is added
5 - Record results to 2 D.P & repeat until you get 2 concordant results
Why do we add excess H2SO4 to the reducing agent in a redox titration
Ensures the presence of sufficient H+ ions to allow reduction of oxidising agent
What ion does MnO4- form when it is reduced
Mn2+
What ion does Cr2O72- form when it is reduced
Cr3+
What does O2 form when it is reduced
H2O
What does C2O4- form when it is oxidised
CO2
What ion foes Fe2+ form when it is oxidised
Fe3+
What is the half equation for when FeC2O4 is oxidised
FeC2O4 —> 2CO2 + Fe3+ + 3e-
What is the half equation for the reduction of MnO4-
MnO4- + 8H+ + 5e- –> Mn2+ + 4H2O
What is the half equation for the reduction of Cr2O72-
Cr2O72- + 14H+ + 6e- → 2Cr3+ + 7H2O
What is the half equation for the reduction of O2 to form water
O2 + 4H+ + 4e- —> 2H2O
What is the half equation for the oxidation of C2O42-
C2O42- → 2CO2 + 2e−
What are the stages in balancing a half equation
1 - Balance elements through coefficients (non Hydrogens or oxygens)
2- Balance oxygens with H2O
3- Balance H’s with H+
4- Balance charge with e-
What is an oxidising agent
A species which is reduced
What is a reducing agent
A species which is oxidised
What is the half equation for the oxidation of Fe2+
Fe2+ —> Fe3+ + e-
What are the two types of catalyst
Homogeneous
Heterogeneous
What is a heterogeneous catalyst
A species that increases the rate of a reaction by providing an alternative reaction pathway of a lower activation energy, which is in a different state to reactants
Give an example of the use of a heterogeneous catalyst
Haber process
Solid iron catalyst is used
Reactants are all gasses and so Fe is a heterogeneous catalyst
Explain how increasing the surface area of a heterogeneous catalyst can increase the rate of reaction
More particles available to react at any given time
What is a homogeneous catalyst
A species that increases the rate of a reaction by providing an alternative reaction pathway of a lower activation energy, which is in the same state as reactants
How do homogeneous catalysts form intermediates
By combining with reactants to form products (the catalyst is then always reformed)
Why are transition metals good catalysts
They have variable oxidation states -they receive and loose some e- in d orbitals to speed up reactions
What is the contact process
The use of vanadium to make H2SO4
State the species and type of catalyst used in the contact process
V2O5
Homogeneous
What reaction does V2O5 catalyse in the contact process
SO2 to SO3
Write the 3 steps in the contact process with equations, and stating which species is oxidised/reduced in each step
What is the benefit of using a catalyst
Faster & lower temperature required which saves money & energy and is also better for the environment
How can impurities cause catalytic poisoning
Impurities bind to the surface of a catalyst which blocks the active sites for reactants to adsorb
How does catalytic poisoning decrease the rate of reaction
Catalytic poisoning decreases the surface area of a catalyst
Give an example of catalytic poisoning. State what the impurity is and what it forms when it adsorbs to the surface of the catalyst
Haber process
H2 is made from methane which contains sulphur impurities
Sulphur which isn’t remove will absorb to the surface forming iron sulphide which makes the iron catalyst less efficient
What is the equation for the Haber process
N2(g) + 3H2(g) —> 2NH3(g)
State 2 reasons why catalytic poisoning is bad
Lowers amount of product made
Catalyst needs to be cleaned or replaced more often
(These increase the cost of the whole process)
Sketch the energy profile for a homogeneous catalyst
What is the overall equation for the oxidation of iodide ions using S2O8-
S2O8-(aq) + 2I-(aq) —-> I2(aq) + 2SO42-(aq)
Why is the uncatalysed reaction of the oxidation of iodide ions using S2O8- very slow
Reacting two negatively charged ions and so they repel, meaning a high activation energy
What catalyst is used in the oxidation of iodide ions using S2O8-. State what type of catalyst this is
Fe2+(aq)
Homogeneous catalyst
Write the two equations displaying the use of an Fe2+ catalyst in the oxidation of iodide ions using S2O8-. State the intermediate formed
(1) S2O8-(aq) + 2Fe2+(aq) —-> 2Fe3+(aq) + 2SO42-(aq)
Fe3+ is intermediate which reacts with I- to produce I2:
(2) 2I-(aq) + 2Fe3+(aq) —> 2Fe2+(aq) + I2(aq)
Catalyst reformed
(Combine both equations to get overall equation)
What is the test for iodine
Starch solution
Blue/black = positive result
What is an autocatalyst
A type of homogeneous catalyst where the product catalyses the reaction
Give an example of autocatalysis
Mn2+ is a catalyst in the reaction between C2O42- and MnO4-
(Mn2+ is product & catalyst)
State what the presence of an autocatalyst means about the rate of a reaction
As the reaction proceeds, amount of product increases and therefore the rate of reaction also increases due to more catalyst present
What is the overall equation of the reaction between MnO4- and C2O42-
Why is the initial reaction between MnO4- and C2O42- very slow
Reacting two negative ions together and so a high activation energy
Write the two steps for the autocatalysis reaction between MnO4- and C2O42-
Draw the routes for Fe
Draw the routes for Cu
Draw the routes for aluminium
Deduce the formula of the linear complex formed when an excess of concentrated hydrochloric acid is added to silver chloride
(AgCl2)-
