TM Revision Flashcards
What is the definition of a transition metal?
An element whose atom has an incomplete d sub level, or one which can give rise to cations with an incomplete d sub level.
In which block do the Transition Metals lie in?
The d block
Give the electronic configuration of Zinc and explain why it isn’t a transition metal.
[Ar]4s24d10, it has a full d orbital.
Give three physical properties of transition metals.
Stronger, denser and less reactive than group 1/2 elements.
Give four chemical properties of transition metals.
Catalytic activity, variable oxidation states, the ability to form complexes, the ability to form coloured ions.
Why do transition metals act as good catalysts?
They have variable oxidation states.
What is a complex ion?
It comprised of a central metal ion surrounded by Ligands.
What is a co-ordinate bond?
When one species donates a pair of electrons to form a covalent bond.
What is a ligand?
An ion or molecule that can donate a pair of electrons to the central metal ion.
Give an example of a unidentate ligand. Why is it unidentate?
Water. It provides one line pair of electrons per molecule. E.g. Cu(H2O)6 2+
Give an example of a bidentate ligand.
C2O4 2-
Give an example of a multidentate ligand.
EDTA 4-
Give an example of an octahedral complex.
Cu( H2O)6 2+
Give an example of a tetrahedral, square planar and linear complex.
CuCl4 2- /cisplatin/Tollen’s reagent (Ag(NH3)2)+
What is haem?
An iron 2 complex with a multidentate ligand.
What is the coordination number?
The number of pairs of electrons donated to the central metal ion.
What can happen to an electron when an atom absorbs energy?
An electron may be promoted from its normal ground state to a higher energy level (excited state).
What sort of energy does it emit when it returns to ground state?
Electromagnetic radiation.
What is the name of the change from one energy level to another?
Electronic transition
Give the equation used to calculate this value and give the meaning of each character.
Delta E = hv
Delta E is the difference in energy (joules)
h = Planck’s constant (6.626 * 10 ^-34)
v = frequency of electromagnetic radiation (Hz)
How does the presence of Ligands affect the d sub level of a metal?
Different Ligands change the amount of d sub level splitting, thus changing the colour.
What three factors of a complex affect it’s colour?
Oxidation state/ ligand/ coordination number
What is the relationship between oxidation state and the amount of d sub level splitting?
The higher the oxidation state, the greater amount of d sub level splitting.
What process is used to measure the concentration of a solution via its amount of absorbed light?
Colorimetry
Describe briefly the process of colorimetry.
The sample is contained in a cuvette. A photocell detects the amount of light transmitted through the sample. The absorbance of light is directly proportional to the concentration of ions in the sample.
In the chromate (CrO4 2-) and dichromate (Cr2O7 2-) equilibrium, the production of which species is favoured by acidic and which by alkaline conditions?
More acidic = dichromate (orange)
More alkaline = chromate (yellow)
What is the chromate and dichromate equilibrium reaction?
Cr2O7 2- + OH- —> 2CrO4 2- + H+
How is Cr3+ formed from dichromate ions? Give the equation and colour change.
Reduced by zinc and dilute HCl.
Cr2O7 2- +14H+ + 3Zn —-> 3Zn2+ + 2Cr3+ + 7H2O
Orange to green colour change.
Describe the conditions and the reaction that occurs to reduce Cr3+ to Cr2+. What is the colour change?
2Cr3+ + Zn —> Zn2+ + 2Cr2+
Inert atmosphere, green to blue
How is Cr3+ oxidised to chromate with hydrogen peroxide? Give the colour change.
2Cr3+ + 10OH- + 3H2O2 —-> 2CrO4 2- + 8H2O
Green to yellow
How is cobalt oxidised with hydrogen peroxide in alkaline conditions?
2Co 2+ + H2O2 —> 2Co 3+ + 2OH-
How do you oxidise cobalt with air in ammoniacal conditions?
Co(H2O)6 2+ + 2NH3 —> Co(H2O)4(OH)2 + 2NH4+
Add XS —> Co(NH3)6 2+ (light brown sol)
Allow to stand in air —> Co(NH3)6 3+ (dark brown solution)
What is a heterogeneous and homogeneous catalyst?
Hetero = in a different phase to reactants homo = in the same phase as reactants, works by forming an intermediate species.
How does V2O5 act as a catalyst in the contact process?
SO2 + 0.5O2 —-> (v2o5 catalyst) SO3
Step one: V2O5 + SO2 —> V2O4 +SO3
Step two: V2O4 + 0.5O2 —> V2O5
What is the catalyst for the Haber process?
Fe
What is Cr2O3 a catalyst for?
The manufacture of methanol from carbon monoxide and hydrogen
What is a support medium used for?
To maximise the surface area of a catalyst.
Give an example of a support medium and its economic advantage.
Catalytic converters contain a ceramic lattice coated with rhodium. Rhodium catalyses the conversion of carbon monoxide and nitrogen monoxide to carbon dioxide and nitrogen. More surface area and lower cost as a thin coating is needed.
Give two examples of catalyst poisoning and their implications.
1) lead can coat the surface of the catalyst in the catalytic converter, so vehicles need unleaded petrol.
2) sulphur poisons iron catalyst in the haber process. Sulphur adsorbs onto the iron forming iron sulphide, and preventing effective reaction. Catalysis.
Why does the Reaction between iodide and peroxidisulphate ions occur slowly?
Negative ions repel each other.
How does Fe2+ catalyse the reaction to form iodine and sulphate ions?
1) S2O8 2- + 2Fe 2+ –> 2Fe 3+ + 2SO4 2-
2) 2Fe 3+ + 2I- —> I2 + 2Fe 2+
(Test for iodine with starch - will turn blue black if present)
Describe the auto catalysis reaction of Mn 2+ between MnO4- + C2O4 2-.
2MnO4- + 16H+ + 5C2O4 2- —> 2Mn 2+ + 8H2O + 10CO2
Catalysis: 4Mn 2+ +MnO4- + 8H+ —> 5Mn 3+ + 4H2O
2Mn 3+ + C2O4 2- —-> 2Mn 2+ + 2CO2
What is the role of Fe in haemoglobin?
Enables oxygen to be transported around the Body. At high O2 conc, oxygen displaces water to form oxyhemoglobin. A low O2 conc, water displaces oxygen to form deoxyhaemoglobin.
Why is CO toxic?
Carbon monoxide is a strong ligand. When it forms carboxyhaemoglobin oxygen cannot displace the carbon monoxide Ligands, starving the body if O2 as it can’t be transported.
What is the use of cisplatin?
It is a complex of platinum with two chloride ions and two ammonia molecules in a square planar shape. Used to treat cancer as it forms coordinate bonds with nitrogen atoms in the DNA so the strands can’t unwind and replicate the DNA.
Give benefits and risks of cisplatin.
Benefits: prevents cell division, inhibits cells division, reducing growth rate of cancer.
Risks: prevents normal cells reproducing, causing hair loss and immune system damage, increasing infection risk. May also cause kidney damage.
What is the formula of Tollen’s reagent and what does it detect?
Ag(NH3)2 +
Reacts to give a silver mirror in the presence of aldehydes.
Does not react with ketones.
