Where are transition metals found in the periodic table?
In the d-block.
Define a transition metal.
A metal that can form one or more stable ions with a partially filled d-subshell.
What is the electronic configuration of Vanadium? Vanadium has 23 electrons in its unionized state.
What orbital fills first, 4s or 3d?
4s fills first.
What orbital empties first 4s or 3d?
How many electrons are in a d-orbital?
What is the electronic configuration of chromium? Chromium has 24 electrons in its unionized state.
What is the electronic configuration of copper? Copper has 29 electrons in its unionized state.
What is the electronic configuration of Ni2+? Nickel has 28 electrons in its unionized state.
What is the electronic configuration of Cr6+? Chromium has 24 electrons in its unionized state.
How many electrons does Argon have?
What feature of transition metals gives them their unusual properties?
Their partially-filled d-subshells.
Why are Zinc and Scandium not transition metals?
They do not form stable ions with partially filled d-subshells. Zn2+ has a full 3d subshell and Sc2+ has an empty 3d subshell.
What are the phsyical properties of transition metals?
High density, high m.p.t. and b.p.t. and they all have similar ionic radii.
What are the unique chemical properties of transition metals?
They can form complex ions.
They form colored ions.
They are excellent catalysts.
They have variable oxidation states.
What is the oxidation state of Maganese in MnO4- ? What colour is MnO4- ?
What colour is Cr2O72- ?
What stable oxidation states is chromium able to exist in?
What colour is Chromium 3+ in aqueous solution, when surrounded by ligands other than water?
Green. If it is surrounded by water ligands, it is violet.
What are the stable oxidation states of Vanadium?
+5, +4, +3, +2
What colour is VO2+?
What colour is VO2+?
What colour is V3+?
What colour is V2+?
What stable oxidation states is Maganese able to form? What are the colours of these states?
MnO4- - 7+ - Purple
Mn2+ - Pink
What colour is Fe3+ in aqueous solution?
What colour is Fe2+ in aqueous solution?
What colour is Co2+ in aqueous solution?
What colour is Ni2+ in aqueous solution? Does Nickel have any other stable oxidation states?
What stable oxidation states is copper able to exist in? What colour is copper 2+ in aqueous solution?
Why are transition metals able to have variable oxidation states?
Because the energy levels of the 4s and 3d subshells are very close together - transition metals can gain and lose different numbers of electrons using similar amounts of energy.
Define the term 'complex ion'
A complex ion is a metal ion surrounded by coordinately bonded ligands.
What is a ligand?
An ion or molecule attached to a metal ion via a coordinate bond or bonds.
If a complex ion has 6 ligands, what shape does it have?
An octahedral shape.
If a complex ion has 4 ligands, what shape does it have? Which of these is the more likely?
Either tetrahedral (bond angle 109.5°) or square planar.
Tetrahedral is the more likely of the two.
In order for a ligand to be a ligand, what feature must it have?
A least one lone pair of electrons.
What are the terms of ligands that form one, two and more coordinate bonds respectively?
Unidentate, bidentate and multidentate
What is haemoglobin?
A protein that transports oxygen around the body.
Describe the structure of haemoglobin.
Octahedral, with four nitrogen atoms forming the 'haem' ring around the cental iron ion (II or III) then the globin is coordinately bonded to the iron from beneath via another nitrogen atom. The oxygen/water is able to coordinately bond to the top of the iron ion.
How are complex ions coloured?
Ligands split the metal ion's 3d subshell into two distinct energy levels. This small energy gap can be traversed by electrons by absorbing light of the correct frequency in the visible spectrum.
What factors affect d-subshell splitting?
Central ion type
Central ion oxidation state
What is the coordination number of a complex ion?
The number of coordinate bonds between the ligands and the central ion.
If a compound does not absorb any frequency of light in the visible spectrum, what colour is it?
What is a chromate (VI) ion?
What is the equilibrium that exists between chromate (VI) and dichromate ions (VI) at equilbrium in aqueous solution? What is the primary factor which that will affect this equilibrium?
Cr2O72-(aq) + H2O(l) 2CrO42-(aq) + 2H+(aq)
pH of the solution - addition of H+ and OH- shift the equlibrium position in opposite directions (H2O provides the hydroxide ions)
What is the half-equation for the reaction of dichromate ions with hydroxide ions?
Cr2O72- + OH- ---> 2CrO4- + H+
What is the half equation for the reaction between an acid and cromate (VI) ions?
2CrO4- + H+ ----> Cr2O72- + OH-
How is it possible to oxidize chromate (III) to chromate (VI) in aqueous solution?
By reacting it with hydrogen peroxide in alkaline solution.
How is it possible to reduce a dichromate to a chromate (III)? What is the equation for this reaction? What is the colour change of this reaction?
Reduce the dichromate with zinc and a dilute acid.
Cr2O72-(aq) + 14H+(aq) + 3Zn(s) ----> 3Zn2+(aq) + 2Cr3+(aq) + 7H2O(l)
Orange to green
What is the equation for the oxidation of Cr3+ to chromate(VI) ions? What are the reagents for this reaction?
2Cr3+(aq) + 10OH-(aq) + 3H2O2(aq) ----> 2CrO4-(aq) + 8H2O(l)
Hydrogen peroxide and alkaline solution
How is it possible to reduce Cr3+ to Cr2+?
What is the equation and colour change for this reaction?
By reacting the Cr3+ with Zinc and dilute acid under an inert atmosphere - Cr2+ highly unstable and oxidized straight back to Cr3+ in air.
2Cr3+(aq) + Zn(s) ----> 2Cr2+(aq) + Zn2+(aq)
Green to blue
What oxidation state does cobalt prefer?
2+ over 3+
How is it possible to form Co3+ from Co2+? What is the equation for this reaction?
By oxidising Co2+ with hydrogen peroxide in alkaline solution, or by reacting it with ammoniacal solution and leaving it open to air.
2Co2+(aq) + H2O2(aq) ----> 2Co3+ + 2OH-(aq)
What is the equation for the oxidation of cobalt by air and ammoniacal solution? What is the sequence of colour changes for this reaction? Why is it necessary to use ammoniacal solution?
[Co(H2O)6]2+(aq) ----> [Co(H2O)4(OH)2](s) -----> [Co(NH3)6]2+(aq) -----> [Co(NH3)6]3+(aq)
Pink ----Add NH3----> Blue ---Excess NH3---> Straw ---Leave to air---> Dark brown
Because [Co(NH3)6]2+ is easier to oxidize than [Co(H2O)6]2+
Why do transition metals make excellent catalysts?
Transition metals have variable oxidation states, meaning they can transfer electrons relatively easily - this speeds up reactions.
What is the contact process?
The combining of Sulphur Dioxide and Oxygen to form Sulphur Trioixide, in the presence of a Vanadium Oxide catalyst.
SO2(g) + 1/2O2(g) ----> SO3(g)
What are the catalysis reactions for the contact process?
V2O5 + SO2 ----> V2O4 + SO3
1/2O2 + V2O5 ----> V2O5
What is the catalyst and equation for the haber process?
N2(g) + 3H2(g) ----> 2NH3(g)
The catalyst for the haber process is iron.
What is the equation and catalyst for the production of methanol from carbon monoxide?
CO(g) + 2H2(g) ----> CH3OH(g)
The catalyst for this process is dichromate (III) - Cr2O3
Define a heterogeneous catalyst.
A catalyst which is in a different phase to the reactants.
What change to a catalyst increase the rate of reaction?
Increasing the surface area of the catalyst - the reactions happen on the surface of the catalyst, so using a lattice structure maximizes surface area and only requires a thin coating of the catalyst.
How can a catalyst be poisoned?
By adsorbing impurities onto its surface, then reacting with those impurities - this reduces the surface area of the catalyst which is able to catalyse the reaction.
Why is a low rate of reaction undesirable?
A low rate of reaction means less product is being produced, which in turn means less profit.
Give two examples of catalyst poisoning.
Lead poisons catalytic converters - unleaded petrol should be used.
Suplhur from the methane used to produce the hydrogen poisons the iron catalyst in the Haber process.
What is a homogeneous catalyst?
A catalyst which is in the same phase as the reactants (usually an aqueous phase).
How does a catalyst work?
By providing the reaction with an alternate pathway of a lower activation energy - the catalyst forms an intermediate species, a process which is of a lower activation energy.
Why is the reaction between S2O82-(aq) slow?
Because both species are negatively charge - they repel one another, making them unlikely to collide and react.
What is the equation for the reaction between S2O82- and I-?
S2O82-(aq) + 2I-(aq) -----> I2(aq) + 2SO42-(aq)
What is the catalyst for the reaction between S2O82- and I-?
Aqueous Iron(II) - Fe2+
Why is Fe2+ used as a catalyst for the reaction between S2O82- and I-?
Because positive species and negative species attract -
S2O82- + 2Fe2+ ----> 2Fe3+ + 2SO42-
2Fe3+ + 2I- ----> 2Fe2+ + I2
What is the test for iodine?
Starch solution - the solution turns black if iodine is present.
What is autocatalysis? What is an example of this?
When a product catalyses the reaction. An example of this Mn2+ in the following reaction:
2MnO4- + 16H+ + 5C2O42- ----> 2Mn2+ + 8H2O + 10CO2
What are the uses of transition metals, besides acting as catalysts?
Fe2+ allows blood to carry oxygen
Cis-platin ([Pt(NH3)2Cl2]) is an anti-cancer drug
What is the reaction between Tollens' reagent and an aldehyde?
RCHO + 2[Ag(NH3)2]+ + 3OH- ----> 2Ag + 4NH3 + 2H2O
What is the reaction between aqueous chromium (III) and sodium hydroxide? What is the redox reaction between the product of this and hydrogen peroxide?
[Cr(H2O)6]3+ + 6OH- ----> [Cr(OH)6]3-(aq) + 3H2O(l)
[Cr(OH)6]3-(aq) + 3H2O2(aq) ----> 2CrO42-(aq) + 2OH-(aq) + 8H2O(l)
Green solution ----> Yellow solution
What colour are chromate (VI) ions in solution?
What colour are chromium (II) ions?