2 Ligands and complex formation

 

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Oxford Textbook Pages : 405 - 412

CGP Revision Guide Pages : 168 - 169

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Show Specification Ref : 5.3.1d, 5.3.1e, 5.3.1f, 5.3.1g

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Question 1 / 5

AQA Jan 2010 Paper 5 Q6 the complex cisplatin acts as an anticancer drug by changing the properties of dna when it reacts with guanine a component of dna areas outside the box will not be scanned for marking cl cl pt nh nh connects to dna chain cisplatin guanine when cisplatin is absorbed into the human body it undergoes a ligand substitution reaction and one chloride ligand is replaced by a water molecule forming a complex ion q a write an equation for this substitution reaction to form the complex ion q marks b the complex ion q can bond to guanine in two different ways b i the first way involves a hydrogen atom from one of the ammonia ligands on q bonding to an atom in a guanine molecule state the type of bond formed to guanine and identify an atom in guanine that could form a bond to this hydrogen atom type of bond atom in guanine marks b ii the second way involves a ligand substitution reaction in which an atom in a guanine molecule bonds to platinum by displacing the water molecule from q state the type of bond formed between guanine and platinum when a water molecule is displaced and identify an atom in guanine that could bond to platinum in this way type of bond atom in guanine marks wmp jan chem c state and explain one risk associated with the use of cisplatin as an anticancer drug risk explanation marks areas outside the box will not be scanned for marking turn over for the next question turn over wmp jan chem
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Question 2 / 5

AQA Jan 2011 Paper 5 Q4 do not write outside the box three characteristic properties of transition metals are complex formation coloured ions and catalytic activity a state the feature of transition metals that gives rise to these characteristic properties mark b state a fourth characteristic property of transition metals mark c for each of the following shapes of complex identify an appropriate example by drawing its structure c i a linear complex c ii a square planar complex c iii a tetrahedral complex question continues on the next page mark mark mark turn over wmp jan chem do not write outside the box d the chemical industry makes use of the catalytic activity of transition metal compounds for example vanadium v oxide is used as a heterogeneous catalyst in the contact process d i write an equation for the overall reaction in the contact process mark d ii explain the meaning of the term heterogeneous as applied to a catalyst mark d iii write two equations to illustrate how vanadium v oxide acts as a catalyst in the contact process equation equation marks d iv suggest what is done to a heterogeneous catalyst such as vanadium v oxide to maximise its efficiency and how this is achieved marks wmp jan chem do not write outside the box e the porphyrin ring is a multidentate ligand that is found in living systems complexed with iron ii ions in haemoglobin and with cobalt ii ions in vitamin b e i give the meaning of the term multidentate mark e ii a porphyrin ring can be represented by the symbol pr it reacts with aqueous iron ii ions as shown in the equation below the enthalpy change for this reaction is approximately zero pr aq fe h o aq fepr h o aq h o i explain why the free energy change for this reaction is negative marks e iii in vitamin b the cobalt ii ion is co ordinated to a porphyrin ring a cyanide cn ion and an additional unidentate ligand the cyanide ion is very toxic predict the co ordination number of the cobalt ion in vitamin b suggest why vitamin b is not toxic co ordination number reason why vitamin b is not toxic marks turn over wmp jan chem
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Question 3 / 5

AQA Jun 2010 Paper 5 Q4 do not write outside the box a transition elements form complex ions with a range of colours and shapes by considering its electron arrangement state how an element can be classified as a transition element mark b explain the meaning of the term complex ion marks c in terms of electrons explain why an aqueous solution of cobalt ii sulfate has a red colour marks d the ligand edta is shown below o o o o ch n ch ch ch h c n h c o o o o d i draw circles around the atoms of two different elements that link to a transition metal ion by a co ordinate bond when edta behaves as a ligand marks d ii write an equation for the reaction between edta and a co h o ion use the abbreviation edta in your equation mark wmp jun chem do not write outside the box d iii explain why the complex ion formed as a product of the reaction in part d ii is more stable than the co h o ion marks e the diagram below shows part of the structure of haemoglobin fe haemoglobin contains an iron ii ion bonded to five nitrogen atoms and one other ligand the fifth nitrogen atom and the additional ligand are not shown in this diagram e i in this diagram bonds between nitrogen and iron are shown as n fe and as n fe state the meaning of each of these symbols meaning of meaning of marks e ii state the function of haemoglobin in the blood mark e iii with reference to haemoglobin explain why carbon monoxide is toxic marks turn over wmp jun chem
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Question 4 / 5

AQA Jun 2013 Paper 5 Q8 do not write outside the box this question explores some reactions and some uses of cobalt compounds a ethanal is oxidised to ethanoic acid by oxygen the equation for this reaction is ch cho o ch cooh this redox reaction is slow at room temperature but speeds up in the presence of cobalt compounds explain why a cobalt compound is able to act as a catalyst for this process illustrate your explanation with two equations to suggest how in the presence of water and hydrogen ions co and then co ions could be involved in catalysing this reaction marks wmp jun chem do not write outside the box b in aqueous solution the co h o ion reacts with an excess of ethane diamine to form the complex ion y b i write an equation for this reaction explain in terms of the chelate effect why the complex ion y is formed in preference to the co h o complex ion marks b ii draw a diagram that shows the shape of the complex ion y and shows the type of bond between the ethane diamine molecules and the cobalt question continues on the next page marks turn over wmp jun chem do not write outside the box c compound z is a complex that contains only cobalt nitrogen hydrogen and chlorine a solid sample of z was prepared by reaction of cm of mol dm aqueous cobalt ii chloride with ammonia and an oxidising agent followed by hydrochloric acid when this sample of z was reacted with an excess of silver nitrate g of silver chloride were obtained use this information to calculate the mole ratio of chloride ions to cobalt ions in z give the formula of the complex cobalt compound z that you would expect to be formed in the preparation described above suggest one reason why the mole ratio of chloride ions to cobalt ions that you have calculated is different from the expected value marks end of questions copyright aqa and its licensors all rights reserved wmp jun chem
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Question 5 / 5

AQA Jun 2014 Paper 5 Q7 section b answer all questions in the spaces provided do not write outside the box the characteristic properties of transition metals include coloured ions complex formation and catalytic activity a consider the chromium complexes p and q cr h o aq red violet cr h o cl aq green explain with reference to oxidation states and electron configurations why the chromium ions in complexes p and q contain the same number of d electrons you should not consider the electrons donated by the ligands explain in terms of electrons why the complexes are different colours you are not required to explain why the observed colours are red violet and green marks wmp jun chem do not write outside the box b write an equation to show how the co nh aq ion reacts with diaminoethane explain the thermodynamic reasons why this reaction occurs marks question continues on the next page turn over wmp jun chem do not write outside the box c the toxic complex cisplatin is an effective anti cancer drug because it reacts with the dna in cancer cells preventing cell division c i draw the displayed structure of cisplatin on your structure show the value of one of the bond angles at platinum state the charge if any on the complex marks c ii when cisplatin is ingested an initial reaction involves one of the chloride ligands being replaced by water write an equation for this reaction mark c iii suggest how the risk associated with the use of this drug can be minimised mark wmp jun chem do not write outside the box d explain with the aid of equations how and why vanadium v oxide is used in the contact process marks turn over for the next question turn over wmp jun chem
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