9701_w10_qp_43
A paper of Chemistry, 9701
Questions:
11
Year:
2010
Paper:
4
Variant:
3
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1
Write equations to illustrate the reactions of the following oxides with water. phosphorus(oxide sulfur(oxide When NO2 reacts with water, nitrogen undergoes a disproportionation reaction in which one nitrogen atom decreases its oxidation number by 1 and another nitrogen atom increases its oxidation number by 1. A mixture of two acids results. Suggest an equation for the reaction between NO2 and water. In a similar disproportionation reaction, Cl O2 reacts with aqueous NaOH to produce a solution containing two chlorine-containing sodium salts. Suggest an equation for the reaction between Cl O2 and aqueous NaOH. The major source of sulfur for the manufacture of sulfuric acid by the Contact process is the de-sulfurisation of ‘sour’ natural gas. Many natural gas wells produce a mixture of volatile hydrocarbons (mainly CH4 and C2H6) together with up to 25% hydrogen sulfide, H2S. Complete and balance the following equation showing the complete combustion of a gaseous mixture consisting of 2 mol of CH4, 1 mol of C2H6 and 1 mol of H2S. 2CH4 + C2H6 + H2S + ______ SO2 + ______ + ______ Explain why it is important to remove the H2S before burning the natural gas industrially. The H2S is removed by passing the ‘sour’ natural gas through a solvent containing ethanolamine. The following reaction takes place. HOCH2CH2NH2 + H2SHOCH2CH2NH3 + + SH– If a sample of natural gas contains 5% by volume of H2S, calculate the mass of ethanolamine required to remove all the H2S from a 1000 dm3 sample of gas, measured under room conditions. For Examiner’s Use The H2S can be recovered by warming the solution to 120 °C, when the above reaction is reversed. The ethanolamine can then be recycled. What type of reaction is occurring here? The recovered H2S is converted to sulfur by the following two reactions. I Part of the H2S is burned in air. H2S + 1.5O2 SO2 + H2O II The gas stream resulting from reaction I is then blended with the remaining H2S and fed into an iron oxide catalyst bed, where sulfur and water are produced according to the following equation. 2H2S+ SO23S+ 2H2OUse the following data to calculate ΔH o–– for the reaction between H2S and SO2. compound ΔH o–– f / kJ mol–1 H2S–21 SO2–297 H2O–242 S+11 ΔH o–– = kJ mol–1
12. Nitrogen and sulfur  →  12.1. Nitrogen and sulfur
11. Group 17  →  11.4. The reactions of chlorine
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For Examiner’s Use Explain why complexes of transition elements are often coloured. When water is added to white anhydrous CuSO4, the solid dissolves to give a blue solution. The solution changes to a yellow-green colour when concentrated NH4Cl is added to it. Concentrating the solution produces green crystals of an ammonium salt with the empirical formula CuN2H8Cl4. Explain these observations, showing your reasoning. Copper can be recovered from low-grade ores by ‘leaching’ the ore with dilute H2SO4, which converts the copper compounds in the ore into CuSO4. The concentration of copper in the leach solution can be estimated by adding an excess of aqueous potassium iodide, and titrating the iodine produced with standard Na2S2O3. 2Cu2+ + 4I– 2CuI + I2 I2 + 2S2O3 2– 2I– + S4O6 2– When an excess of KIwas added to a 50.0 cm3 sample of leach solution, and the resulting mixture titrated, 19.5 cm3 of 0.0200 mol dm–3 Na2S2O3were required to discharge the iodine colour. Calculate the [Cu2+], and hence the percentage by mass of copper, in the leach solution. percentage of copper = %
10. Group 2  →  10.1. Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
11. Group 17  →  11.1. Physical properties of the Group 17 elements
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3
For Examiner’s Use Menthol and menthone, the main constituents of oil of peppermint, can be made synthetically from thymol by the following route. I OH II OH thymol menthol menthone O State the type of reaction of • reaction I, • reaction II. Suggest one test for each of the three compounds that would give a positive result with the stated compound but a negative result with both the other two compounds. thymol test observation menthol test observation menthone test observation
21. Organic synthesis  →  21.1. Organic synthesis
17. Carbonyl compounds  →  17.1. Aldehydes and ketones
14. Hydrocarbons  →  14.2. Alkenes
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For Examiner’s Use The following chart shows some reactions of ethylbenzene and compounds produced from it. Cl NO2 III I II ethylbenzene IV Br Br CO2H V VII X NH2 VI N2Cl O – Na + Draw the structure of compound X in the box provided in the chart above. For Examiner’s Use Suggest reagents and conditions for each of the reactions, writing them in the spaces below. reaction I reaction II reaction III reaction IV reaction V reaction VI reaction VII
15. Halogen compounds  →  15.1. Halogenoalkanes
14. Hydrocarbons  →  14.1. Alkanes
14. Hydrocarbons  →  14.2. Alkenes
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For Examiner’s Use Chlorine is manufactured by the electrolysis of brine, NaCl. At the cathode, H2and OH–are produced, but the product at the anode depends on the [NaCl] in the solution. Either O2or Cl2is produced. The equation for the cathode reaction is 2H2O+ 2e– H2+ 2OH–. Starting from neutral NaCl, write equations for the production at the anode of O2, Cl2. For electrolysis to occur, the voltage applied to the cell must be at least as large as the E o–– cell, as calculated from standard electrode potentials. Use the Data Booklet to calculate E o–– cell for the production at the anode of O2, Cl2. By using one of the phrases more positive, less positive or no change, use the equations you wrote in to deduce the effect of increasing [Cl –] on • the Eanode for the production of O2, • the Eanode for the production of Cl2. Hence explain why the Cl2: O2ratio increases as [NaCl] increases. Sodium chlorate(is prepared commercially by electrolysing NaClin a cell which allows the cathode and anode electrolytes to mix. The cathode reaction is the same as that described in . The equation for the anode reaction is Cl –+ 6OH–– 6e– ClO3 –+ 3H2OConstruct an ionic equation for the overall reaction. For Examiner’s Use Calculate the mass of NaClO3 that is produced when a current of 250 A is passed through the cell for 60 minutes. mass of NaCl O3 = g
11. Group 17  →  11.4. The reactions of chlorine
9. The Periodic Table: chemical periodicity  →  9.2. Periodicity of chemical properties of the elements in Period 3
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For Examiner’s Use The following scheme outlines the production of some compounds from ethene. Br H2C CH2 I Br HO2C CO2H H2N NH2 A B C (C4H4N2) E F D II III SOCl2 KCN, heat in ethanol excess of NH3, heat in ethanol under pressure Suggest the reagent and conditions for reaction I. Describe the mechanism of reaction I by means of a diagram. Include all whole, partial and induced charges, and represent the movements of electron pairs by curly arrows. For Examiner’s Use Suggest the identities of compounds B, C and E, and draw their structures in the boxes opposite. Suggest reagents and conditions for reaction II, reaction III. During reaction II the nitrogen atoms are lost from the organic molecule. Suggest the identity of the nitrogen-containing ion produced during this reaction. Compounds E and F react together to give a polymer and an inorganic product. Draw one repeat unit of this polymer. Identify the inorganic product. A 0.100 mol dm–3 solution of compound D has a pH of 2.60. Calculate the [H+] in this solution. Hence calculate the value of Ka of compound D.
14. Hydrocarbons  →  14.2. Alkenes
15. Halogen compounds  →  15.1. Halogenoalkanes
12. Nitrogen and sulfur  →  12.1. Nitrogen and sulfur
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For Examiner’s Use When an aqueous solution of compound G, NH2CH2CH2CH2NH2, is titrated with HCl, two successive acid-base reactions take place. Write equations for these two acid-base reactions. A 0.10 mol dm–3 solution of G has a pH of 11.3. When 30 cm3 of 0.10 mol dm–3 HCl is added to 10 cm3 of a 0.10 mol dm–3 solution of G, the final pH is 1.6. Using the following axes, sketch the pH changes that occur during this addition of HCl. pH volume of HCladded / cm3
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
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For Examiner’s Use By means of a clear, labelled diagram, describe the shape of the tin(chloride molecule. Explain the shape of the tin(chloride molecule in terms of its bonding. What would you expect to observe when tin(chloride reacts with water? Suggest an explanation for your answer. Write an equation for the reaction between tin(chloride and water.
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
13. An introduction to AS Level organic chemistry  →  13.3. Shapes of organic molecules; σ and π bonds
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9
DNA is an extremely important chemical in human cells. It has been described as the ‘blueprint of life’. What three types of compound are linked together in DNA? DNA consists of two strands linked together. Draw a block diagram to illustrate this and showing two repeat units in the backbones, labelling the components and showing and labelling the bonds between the strands. DNA is used to encode for the production of a particular protein. Put the following biochemical structures in the correct sequence from the use of DNA as a template to the formation of the protein by writing their names in the relevant box below. tRNA mRNA ribosomes DNA ¨ ¨ ¨ ¨ protein For Examiner’s Use In order to produce proteins, the information stored in the DNA molecules has to be translated to produce an mRNA strand. A sequence of three bases, called a triplet, on the mRNA describes a particular amino acid. These amino acids are then combined together to form proteins. The amino acid specified by each triplet is shown below. U U U U U U U U U U U U U U U U C C C C C C C C C C C C C C C C A A A A A A A A A A A A A A A A G G G G G G G G G G G G G G G G U U U U C C C C A A A A G G G G G U A C Val Arg Ser Lys Asn Thr IIe Arg Gln His Pro Leu Leu Phe Ser Tyr Cys Trp Stop Stop Stop Met Start Ala Asp Glu Gly 5’ 3’ 3’ 3’ 3’ The sequence of three bases in a triplet is read from the middle outwards e.g. UGG specifies Trp. There are four different bases present in mRNA. How many different triplets are possible using these four bases. What peptide fragment would the following sequence code for when read from left to right? (Use 3-letter abbreviations for amino acids.) 5’ – A U G A G C C G A C U U G A C G U G – 3’ ………………………………………………………………………………… What would be the effect of changing the 11th base from U to C?
3. Chemical bonding  →  3.4. Covalent bonding and coordinate (dative covalent) bonding
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
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10
For Examiner’s Use 10 Instrumental methods of analysis have become increasingly important in recent years. The use of chromatography to separate substances, and NMR spectroscopy to identify them, has become routine in many laboratories. Chromatography relies on either partition or adsorption to help separate substances. Briefly explain how each method brings about separation. partition adsorption The table shows three different techniques of chromatography. Identify which separation method, partition or adsorption, applies to each. technique separation method paper chromatography thin-layer chromatography gas/liquid chromatography The diagram represents the output from gas/liquid chromatography carried out on a mixture. time injection detector response air peak solvent peak X Y Determine the percentage of each of the two components X and Y in the mixture. For Examiner’s Use NMR spectroscopy is a very important analytical technique for use with organic compounds. Why is NMR spectroscopy particularly useful for organic compounds? Two molecules, propanal and propanone, have the same molecular formula, C3H6O. Draw the displayed formula of each compound and explain briefly how NMR spectroscopy can distinguish between the two structures.
22. Analytical techniques  →  22.2. Mass spectrometry
13. An introduction to AS Level organic chemistry  →  13.1. Formulas, functional groups and the naming of organic compounds
22. Analytical techniques  →  22.1. Infrared spectroscopy
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11
For Examiner’s Use 11 One of the greatest challenges facing scientists today is the development of effective drugs to treat different forms of cancer. Drugs can be introduced into the body by injection or by mouth. Taking drugs by injection avoids the drug being broken down in the digestive system. State two other advantages of giving drugs by injection. The drug Ultiva has been developed to treat ovarian cancer, and is usually given by injection. H3C OCH3 OCH3 O O O N N Ultiva Study the structure of Ultiva and draw a circle around two different functional groups that could be broken down in the digestive system. One way of avoiding the breakdown of drugs in the body is to use a specially designed nanoparticle which encloses the drug. If the nanoparticles are made of a particular sort of polymer, they absorb water at the slightly acidic pH inside some cells, increasing their diameter from around 100 nm to around 1000 nm. This spreads out the polymer chains allowing release of the drug. Other than absorbing water, suggest a property this polymer would need to possess for its use in drug delivery. Why would this method of release not work if the nanoparticles were taken by mouth? For Examiner’s Use Polymers may be formed by two different types of chemical reaction. Name the two types of reaction and write an equation to illustrate each reaction type. name equation name equation The breakdown of polymers, such as carbohydrates and proteins in the body is important for digestion. What type of reaction is generally involved?
11. Group 17  →  11.4. The reactions of chlorine
14. Hydrocarbons  →  14.2. Alkenes
15. Halogen compounds  →  15.1. Halogenoalkanes
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