Transition Metals

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Define a transition element
An element which forms at least one stable ion with a partially full d-shell of electrons
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Where are the transition metals located in the periodic table?
In the middle (from Ti to Cu) part of d-block
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What are some characteristic physical properties of transition metals?
Metallic, good conductors of heat & electricity, hard, strong, shiny, high m.p & b.p, low reactivity
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Some uses of iron?
Vehicle bodies, to reinforce concrete
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What are the chemical properties of transition metals?
Variable oxidation states- can take part in many redox reactions. Coloured compounds/ions in solution. Good catalysts. Form complex ions
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Define the term complex ion
Central metal ion surrounded by ligands that are co-ordinated bonded to it
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Give some examples of transition metals catalysts and the processes/reactions they catalyse?
Iron- Haber process. Vanadium (V) oxide- Contact process. Mn02- decomposition of H2O2
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Which electrons do transition metals lose first when forming ions?
4s
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Define the term ligand
An ion/molecule with at least one lone pair of electrons that donates them to a transition metal ion to form a coordinate bond and thus a complex ion
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Define term mono/unidentate ligand
A ligand that forms one co-ordinate bond to the central metal ion (one lone pair to donate)
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Define the term bidentate ligand
A ligand that forms two co-ordinate bonds to the central metal ion ( 2 lone pairs to donate)
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Define the term multidentate ligand
A ligand that forms three or more co-ordinate bonds to the central metal ion
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Give some examples of common monodentate ligands
Cl-, H2O, NH3, CN-
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Draw ethanedioate, how many co-ordinate bonds can it form to a transition metal ion?
2 co-ordinate bonds
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Draw benzene-1,2-diol; how many co-ordinate bonds can it form to a transition metal ion?
2 co-ordinate bonds
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Draw ethane-1,2-diamine. What is its shortened name? How many co-ordinate bonds does it form?
2 co-ordinate bonds shortened name= en
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How many co-ordinate bonds does EDTA4- form?
six
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Define the term coordination number
The number of co-ordinate bonds the metal ion has formed to surrounding ligands
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What is the Chelate effect?
Chelate complexes with multidentate ligands are favoured over monodentate ligands or ligands that form fewer co-ordinate bonds per molecule
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Explain the Chelate effect in terms of entropy and the reaction that is occuring
Number of molecules increases when multidentate ligands e.g EDTA displace ligands that form fewer co-ordinate bonds per molecule. Significant increase in entropy- Gibb's free energy < 0 so feasible reaction: A more stable complex ion is formed
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What ion is usually formed when a transition metal compound is dissolved in water? What shape is it? Drawn an example
Aqua ion, 6H2O ligands around the central metal ion. Octahedral complex ion is formed
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If a transition metal has 2 ligands what shape is it usually?
Linear
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If a transition metal has 4 ligands what shape is it usually?
Tetrahedral
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Name an exception to the general rule that ions with 4 ligands is generally tetrahedral. What shape is it?
Platin is square planar- forms cisplatin
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What shape is a complex if it has 6 ligands?
Octahedral
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What conditions are needed for a complex ion display to optical isomerism?
Usually applies to octahedral molecules with 2 or more bidentate ligands, so that the mirror images are non-superimposable
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What happens to Co2+, Cu2+ and Fe3+ coordiantion numbers when Cl- ligands replace NH3 or H2O
Decreases from 6 to 4 as Cl- is a much larger ligand than H2O and NH3
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What is haem- its metal ion, coordination number and ligands?
A molecule which makes up protein chains, with an Fe2+ central metal ion which has a coordination number of 6. 4 of these bonds are to a ring called porphyrin. 1 is to the nitrogen of a globin (protein) molecule and one is to an O in an O2 molecule
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How does haemoglobin transport oxygen?
O2 forms a weak coordinate bond to the metal ion, then is transported around the body. The bond breaks when haemoglobin reaches cells and oxygen is released
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Why is CO toxic?
Co also coordinately bonds to the Fe2+ and is a better ligand so bonds more strongly than O2 it stops O2 from bonding to haemoglobin so O2 cannot be transported around the body
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Why are transition metal compounds coloured?
Partially filled d-orbitals, electrons are able to move between d-orbitals. In compounds the d-orbitals spilt into different energy levels. Electrons can absorb energy in form of photons to become excited and move to higher energy level
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Why are transition metal compounds coloured?
(excited level). energy of photon = energy difference between levels. related to frequency of light by E=hf.
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What affects the colour of a transition metal compound?
delta E affects the frequency of absorbed photons so determines the colour. delta E is changed by oxidation state of the metal, number and type of ligands, shape and coordination number
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What can you use to reduce Vanadium?
Zinc
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What colour is Fe2+ aqua ion?
Green
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What colour is Fe3+ aqua ion?
Pale brown
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What colour is Cr2+ aqua ion?
Blue
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What colour is Cr3+ aqua ion?
red/violet
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What colour is Co2+ aqua ion?
Brown
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what colour is Co3+ aqua ion?
Yellow
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What does a colorimeter do?
Measures the absorbance of a particular wavelength of light by a solution
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How would you use colorimetry experimentally?
Use solutions of known concentration to create a calibration graph; find unknown concentration
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What information can a colorimeter give you?
The concentration of a certain ion in the solution
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Why can transiiton metals have variable oxidation states?
They have partially filled d-orbitals so can lose 4s and 3d electrons
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Which oxidarion states do all transition metals have (except Sc)? Why?
+2 because of loss of electrons from 4s
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When oxidation state is high do transition metals exist as simple ions?
No after oxidation state of III metal ions covalently bond to other species
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What is the use of complex [Ag(NH3)2]+ ion?
Tollen's reagant to test for aldehydes/ ketones
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What colour is MnO4-
Deep purple
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What colour is Mn2+
Pink
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Write a half equation for the reduction of MnO4- to Mn2+
Mno4- + 8H+ + 5e- ----> Mn2+ + 4H2O
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Whay are redox reactions titrations with transition metal compounds said to be self-indications?
They usually involve a colour change as the metal is changing oxidation state; sometimes an indicator is still needed/useful
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What colour is Cr2O72-
Orange
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What colour is Cr3+
Green
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Write a half equation for the reduction of Cr2O72- to Cr3+
Cr2O72- + 14H+ +6e- ----> 2Cr£+ + 7H2O
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What happens to aqua metal ions in acidic conditions?
They get reduced
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What happpens to aqua metal ions in alkaline conditions?
they get oxidised
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What happens to aqua metal ions in neutral conditions?
no change
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What does whether reducation/oxidation occurs and readiness of reaction depend on
E circle values
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What can change these E circle values?
pH, ligands involved
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Define a catalyst?
A substance that increases the rate of a reaction without being chemically changed at the end of the reaction
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How do catalysts work?
Provided an alternative reaction pathway with a lower activation energy
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Why are transiton metals good catalysts?
They can exist in variable oxidation states so can provide alternative pathways easily
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Why are group 1,2 and 3 metals not as good catalysts?
Only exist in one oxidation state
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What are the advantages of using a catalyst for a reaction?
allow reactions to proceed at lower temperatures and pressures- saves energy and resources and money
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What metals are used in a catalytic converter and which reactions do they catalyse?
Pt, Rd, Pd: CO, NO ---> CO2, N2 and CxH2x+2 ----> H2O CO2
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Define a heterogeneous catalyst
A catalyst that is present in the reaction in a different phase to the reactants (usually a solid with gas/liquid reactants) Catalytic activity occurs on the solid surface as the reactants pass over it
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What is an advantage of using a heterogeneous catalyst?
No need for separation of products from catalyst
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How do heterogeneous catalysts work?
Reactants adsorb to the catalyst's surface at active sites. This weakens bonds within the reactants, holds reactants close together on the surface and/pr in the correct orientation to react. Once the reaction has occurred, products desorb from the ac
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What properties does the catalyst need to have in order to have to make it a good catalyst?
Can't adsorb too strongly otherwise the products will not desorb. Can't adsorb too wekaly as reactant would not be held in place for long enough and bonds would not be efficiently weakened.
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How can you increase the efficiency of heterogeneous catalysts?
Increase the surface area to increase the number of active sites that are present. Also spread onto an inert support medium e.g ceramic to increase the surface/mass ratio.
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What is catalyst poisoning?
Unwanted impurities adsorb to the catalyst's active sites and do not desorb. This blocks the active sites on the catalyst's surface
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What effect does catalyst poisoning have on catalytic activity?
Decreases the effectiveness of the catalyst over time
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How else can a catalyst be degraded?
Finely divided catalysts can be gradually lost from their support medium
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What is the Haber process? What catalyst is used?
N2 (g) + 3H2 (g) ----> 2NH3 (g) Makes ammonia uses iron (Fe) catalyst
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What size/shape is the catalyst for the Haber process?
Pea sized lumps to increase surface area
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How long does the catalyst last for the Haber process? What is it poisoned by?
About 5 years. Poisoned by sulfur impurities in the gas streams
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What is the Contact process? What is the catalyst?
Makes H2SO4 Catalysed by Vanadium (V) oxide- V2O5. 2SO2 (g) + O2 (g) ---> 2SO3 (g)
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What are the two reactions that are involved in the contact process?
SO2 + V2O5 ---> SO3 + V2O4 & V2O4 +1/2O2 ---> V2O5
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Why is V a good catalyst in the case of the Contact Process?
Can change oxidation state from 5+ to 4+ and back to 5+ so can be used again
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Define a homogeneous catalyst
A catalyst that is in the same phase as the reactants
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How do homogeneous catalysts work?
Form intermediates to give a different reaction pathway with lower Ea
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What is the reaction between S2O82- ions + I- ions
S2O82- + 2I- --->2SO42- + I2 (all aq)
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Why does the reaction between S2O82- ions + I- ions have a high Ea in normal conditions
Two negative ions are reacting they repel each other so Ea is high
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Which transition metal ions catalyse the reaction between S2O82- ions and I- ions? Write two equations
Fe2+ S2O82- + 2Fe2+ -----> 2Fe3+ + 2SO42- & 2Fe3+ + 2I- --> 2Fe2+ + I"
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Define the term autocatalysis
When the product of a reaction is also a catalyst for that reaction
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Write a half equation for the conversion of C2O42- ions into CO2
C2O42 --> 2CO2 + 2e-
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Write an equation for the reaction between C2O42 ions and MnO4- ions.
2MnO4- + 16H+ + 5C2O42- ---> 10CO2 + 2Mn"+ + 8H2O
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Write an equation for the reaction between C2O42 ions and MnO4- ions.
MnO4- + 4Mn"+ + 8H+ ---> 4H2O + 5 Mn3+ & 2Mn3+ + c2O4- ---> 2CO2 + 2Mn2+
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Card 2

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Where are the transition metals located in the periodic table?

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In the middle (from Ti to Cu) part of d-block

Card 3

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What are some characteristic physical properties of transition metals?

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Preview of the front of card 3

Card 4

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Some uses of iron?

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Card 5

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What are the chemical properties of transition metals?

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