F325 A2 Chemistry Unit 2 Transition Metals
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- Created on: 06-02-13 12:44
Define a transition element
A d-block element that forms an ion with an incomplete d sub-shell
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Which two metals in the d block are not transition elements and why?
Zinc and Scandium. Zn only forms the Zn2+ ion in which the d orbitals are full, while Sc only forms Sc3+ in which the d orbitals are empty
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Why is the 4s sub shell filled before the 3d one?
Because it has a lower energy
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Which two transition elements do not follow the Aufbau principle and why not?
Chromium, Cr, as the 3d and 4s orbitals all contain one electron and Copper, Cu, as the 3d orbitals are all full but 4s is only half filled
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Give 3 uses of transition elements
Titanium for joint replacements, Iron for post boxes, Copper, alloyed with nickel to make 'silver' coins
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How many oxidation states can transition elements between Ti and Cu form?
At least 2 each, but up to 7
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What is a catalyst?
A substance that increases the rate of a chemical reaction by providing an alternative route for the reaction to follow without being changed itself
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How do transition metals act as catalysts using adsorption?
Reactants are adsorbed onto the surface of the metal and held in place whilst a reaction occurs. After the reaction, products are desorbed and the metal remains unchanged
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How do transition metals act as catalysts using intermediates?
They can change their oxidation states by gaining or losing electrons. They then bind to reactants forming intermediates as part of a chemical pathway with a lower activation energy
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Outline the Haber Process
N2 + 3H2 <--> 2NH3 using an iron catalyst to increase the rate of reaction and to lower the temperature at which the reaction occurs
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What is the ammonia produced in the Haber Process used for?
Fertilisers
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Outline the Contact Process
2SO2 + O2 <-->2SO3 converting sulfur dioxide into sulfur trioxide as part of the manufacture of sulfuric acid. Vanadium oxide is the catalyst, where it has the oxidation state +5
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What is the sulfuric acid produced in the contact process used for?
Fertilisers, Detergents, Adhesives, Explosives
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Outline the hydrogenation of alkenes
Hydrogen is added across the C=C double bonds in unsaturated compounds to make saturated compounds using a nickel catalyst to lower the temperature and pressure required
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What is are the saturated hydrocarbons produced in hydrogenation used for?
Margarine
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Outline the decomposition of hydorgen peroxide
2H2O2 --> 2H2O + O2 using a manganese dioxide catalyst in the +4 oxidation state
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What is the decomposition of hydrogen peroxide used for?
A simple and convenient source of oxygen gas in laboratories
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Define a precipitation reaction
One in which soluble ions in separate solutions are mixed together to produce an insoluble compound, which settles out of solution as a solide. The insoluble compound is called a precipitate
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What do transition metals ions react with aqueous sodium hydroxide to form?
Coloured precipitates
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What is the equation for the reaction of Cu (II) with NaOH(aq)?
Cu2+ + 2OH- --> Cu(OH)2
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What is the colour change for the reaction of Cu (II) with NaOH(aq)?
Pale blue solution to pale blue precipitate
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What is the equation for the reaction of Co (II) with NaOH(aq)?
Co2+ + 2OH- --> Co(OH)2
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What is the colour change for the reaction of Co (II) with NaOH(aq)?
Pink solution to blue precipitate, which turns beige in the presence of air
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What is the equation for the reaction of Fe (II) with NaOH(aq)?
Fe2+ + 2OH- --> Fe(OH)2
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What is the colour change for the reaction of Fe (II) with NaOH(aq)?
Pale green solution forms a green precipitate, which turns rusty brown in the presence of air
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What is the equation for the reaction of Fe (III) with NaOH(aq)?
Fe3+ + 3OH- --> Fe(OH)3
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What is the colour change for the reaction of Fe (III) with NaOH(aq)?
Pale yellow solution forms a rusty-brown precipitate
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Define the term 'ligand'
A molecule or ion that can donate a pair of electrons to the transition metal ion to form a coordinate bond
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Define the term 'complex ion'
A transition metal ion bonded to one or more ligands by coordinate bonds
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What is another name for a coordinate bond?
A dative covalent bond
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Define the term 'coordination number'
The total number of coordinate bonds formed between a central metal ion and its ligands
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Describe the structure of the complex ion [Cu(H2O)6]2+
There is a central copper 2+ ion surrounded by 6 water molecules acting as ligands, joined by coordinate bonds. It has a coordination number of 6
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What is a requirement for all ligands?
They must have at least one lone pair of electrons in their outer energy level
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What shape does a complex ion with 6 coordinate bonds have?
Octahedral
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What bond angles does an octahedral complex ion have?
90*
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Give an example of an octahedral complex
[Co(H2O)6]2+
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What is a stereoisomer?
A species with the same structural formula but with a different arrangement of atoms in space
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What must an octahedral complex have if it is to form cis/trans isomers?
4 of one type of ligand and 2 of another type
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Which scientist developed the cis-trans ideas in complex ions?
Alfred Werner
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What are the requirements for a cis- isomer of a complex ion e.g. [Co(NH3)4Cl2]+ ?
The two Cl ligands must be at adjacent corners of the octahedron and be at 90 degrees to one another
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What are the requirements for a trans- isomer of a complex ion e.g. [Co(NH3)4Cl2]+ ?
The two Cl ligands must be at opposite corners of the octahedron, at 180 degrees to one another
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What colours are the cis and trans isomers of tetraamminedichlorocobalt?
Cis is purple and trans is green
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What other type of complex ion is cis trans isomerism possible in?
4 coordinate complexes in a square planar shape
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Give an example of a square planar molecule that can achieve cis trans isomerism
[NiCl2(NH3)2]
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What is cis-platin?
An anti cancer drug, the cis isomer of the platinum complex ion [PtCl2(NH3)2]
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How does cis-platin work?
It binds to the DNA of cancer cells, preventing them from reproducing
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Which treatment is cis-platin the basis of?
Chemotherapy
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Name a new cancer drug, say why it was introduced and describe its action
Carbo-platin, as it has fewer unpleasant side-effects than cis-platin. It slows cancer growth by reacting with a cell's DNA
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Explain the term 'bidentate ligand'
A ligand which can donate two lone pairs of electrons to the central metal ion to form 2 coordinate bonds
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Give an example of a bidentate ligand
Ethan -1,2 -diamine, or NH2CH2CH2NH2. This is often shortened to 'en'
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Give an example of a complex ion containing bidentate ligands
[Ni(en)3]2+
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Can cis-trans isomerism occur with bidentate ligands?
Yes
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Give an example of a hexadentate ligand
EDTA
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How does EDTA work?
It reduces the concentration of metal ions in solutions by binding them into complexes
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What are the requirements for optical isomerism?
A complex with 3 molecules of a bidentate ligand OR 2 molecules of bidentate and 2 of monodentate OR 1 of hexadentate
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What are optical isomers?
Non-superimposable mirror images of each other
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What effect do optical isomers have on plane-polarised light?
One of the isomer rotates it clockwise and the other anticlockwise
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Why does a mixture containing equal amounts of both types of optical isomer have no effect on plane-polarised light?
Because the rotations cancel each other out
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Define ligand substitution
A reaction in which one ligand in a complex ion is replaced by another ligand
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What colour is [Cu(H2O)6]2+?
Pale blue solution
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What colour does [Cu(H2O)6]2+ change to with the addition of ammonia?
Deep blue solution
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Describe the product of [Cu(H2O)6]2+ with excess ammonia
[Cu(NH3)4(H2O)2]2+ is deep blue with a distorted octahedral shape
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Why does [Cu(NH3)4(H2O)2]2+ have a distorted octahedral shape?
Because Cu--OH2 bonds are longer than Cu--NH3
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What happens if you add only a little ammonia to the [Cu(H2O)6]2+ ?
Copper (II) Hydroxide precipitate forms
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Describe the reaction of Cu (II) ions with hydrochloric acid
Pale blue --> Green --> Yellow. The reaction exists in equilibrium, and the original colour can be restored by adding water to the yellow solution
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What is the equation for the reaction of Cu (II) with hydrochloric acid?
[Cu(H2O)6]2+ + 4Cl- <--> [CuCl4]2- + 6H2O
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Why does [CuCl4]2- only have 4 ligands?
Chloride ligands are larger than water ligands and have stronger repulsions, so fewer can fit around the central metal ion
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What shape does [CuCl4]2- have?
Tetrahedral, with bond angles of 109.5 degrees
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What colour are aqueous cobalt ions?
Pale pink
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What colour do aqueous cobalt ions change to on the addition of hydrochloric acid?
Dark blue
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Write out the equation for the reaction of cobalt (II) ions with concentrated HCl
[Co(H2O)6]2+ + 4Cl- <--> [CoCl4]2+ + 6H2O
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What does iron allow red blood cells to do and how?
Carr oxygen, as oxygen can only bind to the haem (iron) group of red blood cells
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Describe the coordinate bonds surrounding the iron in a red blood cell haem group
4 between Fe2+ and nitrogen in the haem structure, 1 to the protein globin and 1 to an oxygen molecule
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Define 'the stability constant'
The equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution
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How is 'stability constant' written?
Capital K, little stab
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What is the general equation for Kstab?
Conc. Products over Conc. Reactants
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Why is H2O generally left out of a stability constant equation?
Because all species re dissolved in water, so its concentration is virtually constant
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What does a large value of Kstab imply?
The position of equilibrium lies to the right. The complex ion is stable
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What does a low value of Kstab imply?
That the complex ion is not very stable
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Other cards in this set
Card 2
Front
Which two metals in the d block are not transition elements and why?
Back
Zinc and Scandium. Zn only forms the Zn2+ ion in which the d orbitals are full, while Sc only forms Sc3+ in which the d orbitals are empty
Card 3
Front
Why is the 4s sub shell filled before the 3d one?
Back
Card 4
Front
Which two transition elements do not follow the Aufbau principle and why not?
Back
Card 5
Front
Give 3 uses of transition elements
Back
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