9701_w08_qp_4
A paper of Chemistry, 9701
Questions:
10
Year:
2008
Paper:
4
Variant:
0
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1
Natural bromine consists of the two isotopes 79Br and 81Br in roughly equal proportions. The mass spectrum of bromine consists of 5 peaks. Suggest the mass numbers for the 5 peaks and the identities of the species responsible for them. Suggest the ratios of the relative abundances of • the three lines with the highest mass numbers, • the two lines with the lowest mass numbers. Esters of 2,3-dibromopropan-1-ol with phosphoric acid are useful flame retardants used in plastics and fibres. 2,3-dibromopropan-1-ol can be made from propenal by the following two-stage process. CH2 CH2OH CH2 Br CHO C H II I propenal Br CH 2,3-dibromopropan-1-oI A Examiner’s Use Draw the structure of the intermediate A in the box opposite. Suggest reagents and conditions for • reaction I, • reaction II. The mass spectrum of 2,3-dibromopropan-1-ol includes the following peaks. mass number relative abundance 0.3 0.6 0.3 At what mass number would you expect the molecular ion to occur? Identify the molecular formula (including isotopic composition where relevant) of these 6 peaks. mass number molecular formula
22. Analytical techniques  →  22.2. Mass spectrometry
2. Atoms, molecules and stoichiometry  →  2.1. Relative masses of atoms and molecules
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Use In the late 19th century the two pioneers of the study of reaction kinetics, Vernon Harcourt and William Esson, studied the rate of the reaction between hydrogen peroxide and iodide ions in acidic solution. H2O2 + 2I– + 2H+ 2H2O + I2 This reaction is considered to go by the following steps. step 1 H2O2 + I– IO– + H2O step 2 IO– + H+ HOI step 3 HOI + H+ + I– I2 + H2O The general form of the rate equation is as follows. rate = k[H2O2]a[I–]b[H+]c Suggest how the appearance of the solution might change as the reaction takes place. Suggest values for the orders a, b and c in the rate equation for each of the following cases. case numerical value a b c step 1 is the slowest overall step 2 is the slowest overall step 3 is the slowest overall A study was carried out in which both [H2O2] and [H+] were kept constant at 0.05 mol dm–3, and [I–] was plotted against time. The following curve was obtained. 0.001 0.0009 0.0008 0.0007 0.0006 0.0005 0.0004 0.0003 0.0002 0.0001 120 150 180 210 240 270 300 time / s [I– ion] / mol dm–3 Examiner’s Use To gain full marks for the following answers you will need to draw relevant construction lines on the graph opposite to show your working. Draw them using a pencil and ruler. Calculate the initial rate of this reaction and state its units. rate = units Use half-life data calculated from the graph to show that the reaction is first order with respect to [I–]. Use the following data to deduce the orders with respect to [H2O2] and [H+], explaining your reasoning. [H2O2] / mol dm–3 [H+] / mol dm–3 relative rate 0.05 0.05 1.0 0.07 0.05 1.4 0.09 0.07 1.8 order with respect to [H2O2] = order with respect to [H+] = From your results, deduce which of the three steps is the slowest (rate determining) step.
8. Reaction kinetics  →  8.1. Rate of reaction
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Use Describe and explain the trend observed in the thermal stability of the carbonates of the Group II elements. By quoting suitable data from the Data Booklet suggest how the thermal stabilities of • zinc carbonate and • lead carbonate might compare to that of calcium carbonate. Malachite is an ore of copper. It contains the following percentages by mass. copper 57.7% oxygen 36.2% carbon 5.4% hydrogen 0.9% Malachite reacts with dilute H2SO4 producing a gas B that turns limewater milky and leaving a blue solution C. When heated in the absence of air, malachite produces gas B and steam, and leaves a black solid D. D reacts with dilute H2SO4 to produce the same blue solution C. Adding iron filings to C produces a pink solid E and a pale green solution F. Calculate the empirical formula of malachite. Examiner’s Use Suggest the formula of the ion responsible for the blue colour of solution C. Identify the black solid D and calculate the mass of D that could be obtained by heating 10 g of malachite. Use data from the Data Booklet to identify the pink solid E and the solution F, and suggest an equation for the reaction producing them. What type of reaction is the reaction that produces E and F? Describe and explain what you would see happen when dilute NH3is added slowly to the solution C until it is in an excess.
10. Group 2  →  10.1. Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
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Use The viscosity of engine oil can be improved by the addition of certain medium chain- length polymers. A portion of the chain of one such polymer is shown below. –CH2CH(CH2CH2CH3)CH2CH(CH2CH2CH3)CH2– On average, the molecules of the medium-chain polymer contain 40 carbon atoms. Suggest the structure of the monomer. How many monomer units are incorporated into the average molecule of the polymer? Used car engine oil can be recycled for use as a fuel by the processes of distillation and cracking. Assuming a typical molecule of engine oil has the formula C40H82, suggest an equation for a cracking reaction that could produce diesel fuel with the formula C16H34 and other hydrocarbons only. What conditions are needed for this cracking reaction? Considering only the bonds broken and the bonds formed during the reaction, use the Data Booklet to calculate the enthalpy change for the reaction you wrote in . Comment on how the conditions you described in relate to the enthalpy change you calculated in .
14. Hydrocarbons  →  14.1. Alkanes
14. Hydrocarbons  →  14.2. Alkenes
5. Chemical energetics  →  5.1. Enthalpy change, \(\Delta H\)
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Use (4-aminophenyl)ethanoic acid (4-APEA) and its derivatives are being investigated as possible drugs to treat chronic inflammation of the intestines. The synthesis of 4-APEA from methylbenzene is shown in the following scheme. CH3 I II CH2Cl G H3O+ HNO3 + H2SO4 NO2 NO2 V IV III H CH2CN NH2 4-APEA CH2CO2H Draw the structures of the compounds G and H in the boxes above. Suggest reagents and conditions for the following steps. • step II • step III • step V
14. Hydrocarbons  →  14.2. Alkenes
21. Organic synthesis  →  21.1. Organic synthesis
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Use Suggest a test or simple reaction you could carry out on each of the following pairs of compounds to enable them to be distinguished. CH3COCH2CH2CH3 CH3CH2COCH2CH3 J K description of test or reaction observation with compound J observation with compound K NH2 NH2 L M description of test or reaction observation with compound L observation with compound M Examiner’s Use CH3CH2COCl CH3CH2CH2Cl N P description of test or reaction observation with compound N observation with compound P CH3CH2CONH2 CH3CH2CH2NH2 Q R description of test or reaction observation with compound Q observation with compound R
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
17. Carbonyl compounds  →  17.1. Aldehydes and ketones
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Use Explain briefly what is meant by the word protein. Describe how peptide bonds are formed between amino acids during the formation of a tripeptide. Include diagrams and displayed formulae in your answer. Describe how proteins can be broken down into amino acids in the laboratory without the aid of enzymes. When a small polypeptide S was broken down in this way, three different amino acids were produced according to the following reaction. CH2 S Mr = 165 2 NH2CHCO2H CH3 Mr = 89 2 NH2CHCO2H + Mr = 75 3 NH2CH2CO2H + How many peptide bonds were broken during this reaction? Calculate the Mr of the polypeptide S. Mr =
3. Chemical bonding  →  3.4. Covalent bonding and coordinate (dative covalent) bonding
13. An introduction to AS Level organic chemistry  →  13.3. Shapes of organic molecules; σ and π bonds
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Enzymes play a vital role in all living organisms, helping chemical reactions to take place at body temperature. The diagram below shows the reaction pathway of an enzyme-catalysed reaction without an enzyme present. On the diagram sketch the pathway if the enzyme was present. energy reaction pathway reactants products What type of molecule are most enzymes? Why do many enzymes lose their catalytic effectiveness above 40 °C? Explain the difference between competitive and non-competitive inhibition of an enzyme. Examiner’s Use The graph below shows how the rate of an enzyme-catalysed reaction varies with substrate concentration in the absence of an inhibitor. For a given amount of enzyme, Vmax represents the rate when all of the active sites on the enzyme are being used. reaction rate substrate concentration Vmax Sketch on the diagram curves to show the effect on the rate of reaction of: I a competitive inhibitor; II a non-competitive inhibitor. Clearly label your curves. Heavy metal ions like Hg2+ can bind irreversibly to enzymes and this can result in poisoning. Suggest to what atom or group Hg2+ ions bind. Explain how this affects enzyme activity.
8. Reaction kinetics  →  8.2. Effect of temperature on reaction rates and the concept of activation energy
8. Reaction kinetics  →  8.3. Homogeneous and heterogeneous catalysts
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Use The technology of DNA fingerprinting has enormously advanced scientific identification techniques in medicine, crime detection and archaeology in recent years. In order to prepare a DNA sample for analysis, the DNA is treated with restriction enzymes. What do restriction enzymes do? What is the next stage in DNA analysis, after the treatment with restriction enzymes? How are the DNA fragments made visible? NMR and X-ray crystallography have made significant contributions to our knowledge of the structure of proteins and, in the pharmaceutical industry, how drugs react with target proteins. Suggest an advantage of each technique in helping to determine protein structure. MRI scanning is a medical technique based on NMR spectroscopy. It is particularly useful for looking for tumours in healthy tissue. Suggest how this technique can distinguish tumour tissue from healthy tissue. Examiner’s Use A saturated molecule of formula CxHyNO was subjected to analysis by mass spectrometry and NMR spectroscopy. In the mass spectrum of the compound, the M peak was at m/e 73 and the ratio of the heights of the M:M+1 peak was 48 : 1.7. Using the data from the mass spectrum, determine the values of x and y in the formula of the compound. Use the data from together with the NMR spectrum below to deduce a structure for the compound, explaining how you arrive at your answer. chemical shift,  / ppm
22. Analytical techniques  →  22.2. Mass spectrometry
22. Analytical techniques  →  22.1. Infrared spectroscopy
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Use 10 Silk from silkworms, used as a fabric shows a different secondary structure to that produced by spiders. silkworm silk spider dragline silk less ordered  sheets glycine rich strand highly ordered  sheets What sort of bonding would you expect to occur between adjacent parts of the protein chains in each form of silk? silkworm spider Suggest two differences in properties that these forms of silk could have. Explain your answer. Spider dragline silk contains large amounts of the amino acid glycine. How does this affect the properties of the silk? Examiner’s Use Both forms of silk are condensation polymers. Explain what is meant by a condensation polymer. Another type of polymer is called an addition polymer. Name an example of an addition polymer. Suggest why condensation polymers such as proteins show a wider range of properties than addition polymers.
20. Polymerisation  →  20.1. Addition polymerisation
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