9701_s08_qp_4
A paper of Chemistry, 9701
Questions:
10
Year:
2008
Paper:
4
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0
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1
Chlorine gas and iron(ions react together in aqueous solution as follows. Cl 2 + 2Fe2+ 2Cl – + 2Fe3+ The following diagram shows the apparatus needed to measure the E o cell for the above reaction. V S A B C E D In the spaces below, identify what the five letters A – E in the above diagram represent. A B C D E Use the Data Booklet to calculate the E o cell for this reaction, and hence decide which direction (left to right, or right to left) electrons would flow through the voltmeter V when switch S is closed. E o cell = V direction of electron flow Examiner’s Use Iron(chloride readily dissolves in water. FeCl 3Fe3++ 3Cl –Use the following data to calculate the standard enthalpy change for this process. species DH o f / kJ mol–1 FeCl 3–399.5 Fe3+–48.5 Cl ––167.2 DH o = kJ mol–1 A solution of iron(chloride is used to dissolve unwanted copper from printed circuit boards. When a copper-coated printed circuit board is immersed in FeCl 3, the solution turns pale blue. Suggest an equation for the reaction between copper and iron(chloride and use the Data Booklet to calculate the E o for the reaction. equation E o = V
11. Group 17  →  11.4. The reactions of chlorine
14. Hydrocarbons  →  14.2. Alkenes
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Use This question is about the properties and reactions of the oxides of some elements in their +4 oxidation state. Chlorine dioxide, Cl O2, is an important industrial chemical, used to bleach wood pulp for making paper, and to kill bacteria in water supplies. However, it is unstable and decomposes into its elements as follows. 2Cl O2Cl 2+ 2O2The chlorine atom is in the middle of the Cl O2 molecule. Using the chlorine-oxygen bond energy as 278 kJ mol–1, and other values from the Data Booklet, calculate DH for the above reaction. DH = kJ mol–1 Assuming the Cl -O bonds in chlorine dioxide are double bonds, predict the shape of the Cl O2 molecule. Explain your answer. Cl O2 can be made in the laboratory by reacting KCl O3 with concentrated H2SO4. Other products are K2SO4, KCl O4 and H2O. Construct a balanced equation for this reaction. You may find the use of oxidation numbers helpful. Sulphur dioxide is an atmospheric pollutant. State two sources of atmospheric SO2 that arise from human activity. Explain why SO2 is a pollutant, and state an environmental consequence of this pollution. Examiner’s Use All the oxides of the elements in Group IV in their +4 oxidation state are high melting point solids except CO2. Explain this observation by describing the bonding in CO2, SiO2 and SnO2. State the difference in the thermal stabilities of SnO2 and PbO2. Illustrate your answer with an equation. CO2 dissolves in water to form a weakly acidic solution containing the hydrogencarbonate ion. Write an equation for the reaction of CO2 with water, and write an expression for the equilibrium constant, Kc. Explain the role of the hydrogencarbonate ion in controlling the pH of blood, illustrating your answer with relevant equations.
9. The Periodic Table: chemical periodicity  →  9.2. Periodicity of chemical properties of the elements in Period 3
11. Group 17  →  11.4. The reactions of chlorine
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Use The elements of Group IV all form tetrachlorides with the general formula M Cl 4. Draw a diagram of a molecule of SiCl 4 stating bond angles. Describe and explain how the volatilities of the Group IV chlorides vary down the group. The relative stabilities of the M 2+and M 4+ions also vary down Group IV. Use the Data Booklet to illustrate this observation when M = Sn and M = Pb. Use the Data Booklet to predict the products formed, and write equations for the reactions occurring, when • an equimolar mixture of Sn2+and Sn4+is added to I2, • an equimolar mixture of Pb2+and Pb4+is added to SO2. Examiner’s Use The Sn–Cl bond energy is +315 kJ mol–1. Use this and other values from the Data Booklet to calculate DH o for the reaction M Cl 2+ Cl 2M Cl 4for the following cases. • M = Si DH o = kJ mol–1 • M = Sn DH o = kJ mol–1 Do your results agree with the trend in relative stabilities of the +2 and +4 oxidation states in ? Explain your answer.
11. Group 17  →  11.2. The chemical properties of the halogen elements and the hydrogen halides
9. The Periodic Table: chemical periodicity  →  9.2. Periodicity of chemical properties of the elements in Period 3
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Use Recently much interest has been shown in the production of the fuel biodiesel from algae. Up to 55% of the mass of the dried algae is composed of lipids, the majority of which are triglycerides. To convert triglycerides into biodiesel, the following processes are carried out. C17H35CO2CH2 3C17H35CO2H C17H35CO2H C17H35CO2CH2 a triglyceride, Mr = 890 biodiesel, Mr = 298 C17H35CO2CH CH2OH C17H35CO2CH3 CH2OH glycerol CHOH + I II Name the functional group present in triglycerides. Suggest reactants and conditions for reaction I, reaction II. Suggest the structural formula of the compound formed when glycerol is reacted with an excess of HBr, an excess of hot acidified K2Cr2O7. Examiner’s Use Calculate the mass of biodiesel that can be produced from 1000 kg of dried algae, assuming that 50% of the algal mass is triglycerides. mass = kg Construct an equation for the complete combustion of biodiesel. Use your equation to calculate the mass of CO2 produced when 10 kg of biodiesel is burned. The production of biodiesel is at present an expensive process. Suggest a reason why the development of biodiesel as an alternative to fossil fuels is important.
2. Atoms, molecules and stoichiometry  →  2.4. Reacting masses and volumes (of solutions and gases)
14. Hydrocarbons  →  14.1. Alkanes
16. Hydroxy compounds  →  16.1. Alcohols
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Use Both ethene and benzene react with bromine, but the mechanisms and the types of products of the two reactions are different. Br2 Br BrCH2CH2Br H2C CH2 + HBr + reaction I no heat, no light, no catalyst needed Br2 + reaction II heat and catalyst needed State the type of reaction undergone in each of reactions I and II. reaction I reaction II Examiner’s Use In each of reactions I and II, the intermediate is a bromine-containing cation. In each of the following boxes, draw the intermediate and use curly arrows to show how it is converted into the product. reaction I product intermediate reaction II product intermediate Why do ethene and benzene differ in their reaction with bromine?
14. Hydrocarbons  →  14.2. Alkenes
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The substituted benzene compound can be further substituted. If Y is an electron-withdrawing group, the next substitution will be in position 3. If Y is an electron-releasing group, the next substitution will be mostly in position 4. X + X if Y is electron-withdrawing + X if Y is electron-releasing Y Y Y X The following table lists some electron-withdrawing and electron-releasing substituents. electron-withdrawing groups electron-releasing groups –NO2 –CH3 –COCH3 –CH2Br –CO2H –NH2 Use the above information to draw relevant structural formulae in the boxes in the schemes below. CH3 H+ KMnO4 + OH– H+ KMnO4 + OH– OH– Sn + HCl Br2 + Al Cl 3 E D C B A HNO3 + H2SO4
15. Halogen compounds  →  15.1. Halogenoalkanes
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
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Use Each of the following structures is an 8-atom segment of the chain of a commercial polymer. For each structure, • decide whether it is part of a condensation or an addition polymer, and • draw the structural formulae of the monomerfrom which the polymer is made. polymer addition or condensation? formulae of monomers H N H N CH2 CH2 O C H N O C O C O O O C CH2 CH2 CH2 CH3 CH3 CH CH O C CONH2 CH2 CH CH2 CH CH2 CH CH2 CH CH3 CONH2
20. Polymerisation  →  20.1. Addition polymerisation
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State and show, using suitable diagrams, the types of bonding that occur in the primary, secondary and tertiary structures of a protein. primary secondary tertiary Analysis of a polypeptide A showed that the amino-(N-)terminal end is methionine and that the carboxyl-(C-)terminal end is lysine . Enzymic hydrolysis of the polypeptide produced the following tripeptides, with the amino acid residue on the left having the free amino group. met-ala-gly gly-arg-val ala-gly-arg arg-val-lys ala-gly-ala gly-ala-gly Work out the sequence of amino acids in A, using the 3-letter abbreviations. Use each tripeptide once only. Examiner’s Use Give two examples of how interchanging the positions of two amino acids could affect the bonding in, and hence the overall structure of, the protein.
3. Chemical bonding  →  3.4. Covalent bonding and coordinate (dative covalent) bonding
4. States of matter  →  4.2. Bonding and structure
13. An introduction to AS Level organic chemistry  →  13.3. Shapes of organic molecules; σ and π bonds
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Use Much of the preparation of evidence to solve crimes now relies on instrumental analysis. This question deals with some of the techniques used. Electrophoresis can be used to separate amino acids produced by hydrolysing proteins. The amino acids are placed in a buffered solution in an electric field. In a solution of given pH, what two factors affect the movement of a given amino acid? Nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry are also used in the detection of certain molecules, particularly those containing hydrogen atoms. Explain how and why the NMR spectrum of propanal, CH3CH2CHO, would be different from that of propanone, CH3COCH3, which contains the same atoms. Explain how and why the mass spectrum of the two compounds in would be different. Examiner’s Use At one time, bromomethane, CH3Br, was widely used to control insect pests in agricultural crops and timber. It is now known to break down in the stratosphere and contribute to the destruction of the ozone layer. Samples can be screened for traces of bromomethane by subjecting them to mass spectrometry. Which peakwould show the presence of bromine in the compound? How could you tell by studying the M and M+2 peaks that the compound contained bromine rather than chlorine?
22. Analytical techniques  →  22.2. Mass spectrometry
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Use 10 A number of drugs, such as insulin for diabetics, are delivered by injection rather than by mouth (oral delivery). Suggest two reasons why this might be necessary. Many patients prefer oral delivery to injection, and a number of methods for overcoming the problems of oral delivery are being investigated. Several of these use nanotechnology. Study the passage and diagram and then answer the questions that follow. At a 2004 meeting, engineers from the University of Texas described their research into nanospheres for oral drug delivery. Nanospheres can transport a drug safely through the hostile environment of the stomach. The nanospheres are created from hydrogels which are stable, organic materials formed from a network of polymer chains. Hydrogels have a variety of uses including disposable nappies, soft contact lenses, dressings for burns and, more recently, drug delivery. The drug is contained in the hydrogel nanosphere as shown in the diagram below. Hydrogels absorb water and swell at a rate dependent on the pH of their environment. As the hydrogel swells, the drug is released. capsule containing nanospheres nanosphere hydrogel coat drug What is a nanosphere? Suggest why the stomach might be a particularly hostile environment for drugs. Examiner’s Use Suggest two ways in which the nanosphere shown in the diagram can be modified to change the rate of drug release. Hydrogels may be formed as homopolymers (using a single monomer), or heteropolymers (using two or more different monomers). By using the monomers below, you are to draw sections of both a homopolymer and a heteropolymer. Each of your drawings should show a three-monomer section of the polymer. HOCH2CH2OH HO2CCHRNH2 HO2CCH(OH)CH2CO2H homopolymer heteropolymer
20. Polymerisation  →  20.1. Addition polymerisation
14. Hydrocarbons  →  14.2. Alkenes
18. Carboxylic acids and derivatives  →  18.2. Esters
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