9701_w12_qp_43
A paper of Chemistry, 9701
Questions:
8
Year:
2012
Paper:
4
Variant:
3
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1
Write down what you would see, and write equations for the reactions that occur, when magnesium chloride, aluminium chloride and silicon tetrachloride are separately mixed with water. magnesium chloride aluminium chloride silicon tetrachloride Sodium chloride is traditionally added to a particular meat product. In response to the evidence that sodium chloride can lead to high blood pressure, the manufacturers have replaced the sodium chloride with a mixture of sodium and potassium chlorides. 100 g of the meat product usually contains about 2 g of the chloride mixture. A particular meat product contains 1.10 g of sodium chloride and 0.90 g potassium chloride in 100 g. Calculate the number of moles of chloride ions in 100 g of this meat product. The amount of chloride in the meat product can be found by titration with silver nitrate solution. Write the ionic equation, including state symbols, for the reaction between aqueous sodium chloride and aqueous silver nitrate. For Examiner’s Use The chlorides from 100 g meat product are extracted into water and the solution made up to 1000 cm3 in a volumetric fl ask. A 10.0 cm3 portion of this solution is then titrated with 0.0200 mol dm–3 silver nitrate solution to precipitate the chloride. Calculate the volume of 0.0200 mol dm–3 silver nitrate solution that would be required if this titration were carried out on 100 g of the particular meat product described above. The iodination of benzene requires the presence of nitric acid. Using bond enthalpies from the Data Booklet, calculate the enthalpy change for the following reaction. + I2 + HI I → Nitric acid reacts with hydrogen iodide according to the following unbalanced equation. HI + HNO3 → I2 + N2O3 + H2O Balance this equation, and describe how the oxidation numbers of nitrogen and iodine have changed during the reaction. nitrogen iodine
11. Group 17  →  11.4. The reactions of chlorine
11. Group 17  →  11.3. Some reactions of the halide ions
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For Examiner’s Use Nitrogen oxides in the atmosphere are homogeneous catalysts in the formation of acid rain. What is meant by the following terms? catalyst homogeneous State a major source of nitrogen oxides in the atmosphere, explaining how they are formed. Use equations to describe the chemical role played by nitrogen oxides in the formation of acid rain. For Examiner’s Use Use the following axes to draw a fully labelled reaction pathway diagram showing the effect of a catalyst on an exothermic reaction. Label the ∆H and Ea values. energy extent of reaction reactants
12. Nitrogen and sulfur  →  12.1. Nitrogen and sulfur
8. Reaction kinetics  →  8.3. Homogeneous and heterogeneous catalysts
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For Examiner’s Use Complete the following electronic confi guration of the Cu2+ ion. 1s2 2s2 2p6 In a free, gas-phase transition metal ion, the d-orbitals all have the same energy, but when the ion is in a complex the orbitals are split into two energy levels. Explain why this happens. How does this splitting help to explain why transition metal complexes are often coloured? Why does the colour of a transition metal complex depend on the nature of the ligands surrounding the transition metal ion? Draw a fully-labelled diagram of the apparatus you could use to measure the E o of a cell composed of the Fe3+/Fe2+ electrode and the Cu2+/Cu electrode. For Examiner’s Use The E o for Cu2+/Cu is +0.34 V. When NH3is added to the electrode solution, the Eelectrode changes. Describe the type of reaction taking place between Cu2+and NH3. Write an equation for the reaction. Describe the change in the colour of the solution. Predict and explain how the Eelectrode might change on the addition of NH3. Fehling’s reagent is an alkaline solution of Cu2+ ions complexed with tartrate ions. It is used in organic chemistry to test for a particular functional group. Name the functional group involved. Describe the appearance of a positive result in this test. Write an equation for the reaction between Cu2+ and OH– ions and a two-carbon compound containing the functional group you named in . A solution containing a mixture of tartaric acid and its sodium salt is used as a buffer in some pre-prepared food dishes. Calculate the pH of a solution containing 0.50 mol dm–3 of tartaric acid and 0.80 mol dm–3 sodium tartrate. [Ka(tartaric acid) = 9.3 × 10–4 mol dm–3] pH =
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
11. Group 17  →  11.3. Some reactions of the halide ions
14. Hydrocarbons  →  14.2. Alkenes
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For Examiner’s Use The compound responsible for the yellow colour of the spice turmeric is curcumin. Its molecular structure can be deduced from the following series of reactions. The CH3O – group that is present in curcumin may be regarded as unreactive. curcumin, C21H20O6 reaction 1 hot concentrated acidified KMnO4 + (one mole) (two moles) A, C5H4O6 B, C5H8O6 C, C5H6N2O2 D, C9H10O3 reaction 2 reaction 4 reaction 5 HCN + NaCN reaction 3 CO2H CH3O HO 1. I2 + OH–2. H+CHO CHO H2C Curcumin and compounds A and D all react with 2,4-dinitrophenylhydrazine reagent. Compounds A and B effervesce with Na2CO3, but curcumin, and compounds C and D, do not. Curcumin reacts with Br2and with cold dilute acidifi ed KMnO4 For Examiner’s Use Name the functional group common to curcumin and compounds A and D. Name the functional group common to compounds A and B. Suggest the structures of compounds B, C and D, and draw their structural formulae in the relevant boxes opposite. Suggest suitable reagents and conditions for reaction 4. Name the type of reaction for reaction 2. Suggest a reagent for reaction 2. Suggest the structure of compound A, and draw its structural formula in the relevant box opposite. Name the functional group in curcumin that reacts with cold dilute acidifi ed KMnO4. Name two functional groups in curcumin that react with Br2. Suggest a structure for curcumin and draw its structural formula in the relevant box opposite.
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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For Examiner’s Use Explain why ethylamine is basic. Write an equation showing ethylamine acting as a base, a nucleophile. Why is phenylamine less basic than ethylamine? Alkaloids are naturally-occurring compounds that act as bases. Suggest the structure of the product, E, of the reaction between the alkaloid nicotine and an excess of HCl . E excess HCl nicotine N N CH3 Phenylamine, and substituted phenylamines, are used to make cloth dyes and food colourants. The fi rst step in this process is the production of a diazonium salt. NH2 N N + State the reagents and conditions necessary for this reaction. For Examiner’s Use The diazonium salt is then reacted with a phenol or an aryl amine in alkaline solution. N N N OH N + OH + NaOHNR2 + NaOHN N NR2 Suggest the starting materials needed to synthesise the following dyes. Draw their structures in the boxes provided. N N OH O2N CO2H alizarin yellow R N N N(CH3)2 methyl orange NaO3S Suggest what effect the NaO3S – group in methyl orange has on its properties. This group has no effect on the colour of the compound.
16. Hydroxy compounds  →  16.1. Alcohols
14. Hydrocarbons  →  14.2. Alkenes
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The proteins in the human body are complex polymers made up of around 20 different amino acids. Alanine is a typical amino acid. N C O OH H H alanine CH3 H C Glycine, H2NCH2CO2H, is the simplest amino acid and differs from each of the other 2-amino acids in a signifi cant way. What is this difference? Protein molecules coil and fold, producing molecules with complex three-dimensional shapes. This is referred to as the secondary and tertiary structures of a protein. State one form of secondary structure and give the type of bonding responsible. structure bonding Give two examples of bonding causing the tertiary structure, and give the amino acid responsible in each case. bonding amino acid bonding amino acid Suggest why globular proteins, such as enzymes, contain relatively small amounts of glycine and alanine when compared to the amounts of some other amino acids. You may wish to refer to their structures given above. For Examiner’s Use DNA consists of a double helix with each strand having a sugar-phosphate ‘backbone’ with one of four bases – adenine (A), cytosine (C), guanine (G) and thymine (T) – attached to the sugar. The two strands of the double helix are held together by hydrogen bonds between pairs of bases. What are the pairs of bases? In protein synthesis, sections of the DNA are copied by mRNA and this, in turn, is read by the ribosome in order to assemble the amino acids for the new protein chain. Each group of three bases codes for one amino acid, with some amino acids having several codes. The codes are summarised below. UUU UUC UUA UUG phe phe leu leu UCU UCC UCA UCG ser ser ser ser UAU UAC UAA UAG tyr tyr stop stop UGU UGC UGA UGG cys cys stop trp CUU CUC CUA CUG leu leu leu leu CCU CCC CCA CCG pro pro pro pro CAU CAC CAA CAG his his gln gln CGU CGC CGA CGG arg arg arg arg AUU AUC AUA AUG ile ile ile met/ start ACU ACC ACA ACG thr thr thr thr AAU AAC AAA AAG asn asn lys lys AGU AGC AGA AGG ser ser arg arg GUU GUC GUA GUG val val val val GCU GCC GCA GCG ala ala ala ala GAU GAC GAA GAG asp asp glu glu GGU GGC GGA GGG gly gly gly gly The coding for all protein chains starts with the AUG, and ends with one of three ‘stop’ codes shown in the table. What amino acid sequence would the following series of bases produce? -AUGGGUAGCCUCGCAUCGUAA- What would be the effect on the amino acid sequence, of a mutation that changed the base at position 10 in the series of bases above from C to G?
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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For Examiner’s Use Although the chemical reactions of compounds remain important pointers to their functional groups, instrumental techniques such as mass spectrometry and NMR spectroscopy are increasingly used to determine molecular structures. Compound J was analysed using these two techniques with the following results. The mass spectrum showed that ● the M peak was at m/e 86, ● the ratio of heights of the M and M+1 peaks was 23.5 : 1.3. The NMR spectrum is shown below. δ / ppm Use the data to determine the number of carbon and hydrogen atoms present in J, showing your working. Use the information given above and your answer to to identify the other element present in J. Determine the structure of J, explaining how you reach your conclusion. structure of J explanation For Examiner’s Use Chromatography is another important analytical technique used in chemistry. Paper, thin-layer and gas-liquid chromatography rely on different physical methods to separate the components in a mixture. Complete the table indicating the appropriate method on which the technique is based. technique physical method paper chromatography thin-layer chromatography gas-liquid chromatography In paper chromatography, better separation may be achieved by running the chroma- togram in one solvent, then turning the paper at right angles and running it in a second solvent. The chromatogram below was produced in this way. solvent 1 solvent 2 sample applied here How many spots were visible before solvent 2 was used? Ring the spot that did not move in solvent 2. How many spots travelled further in solvent 2 than they did in solvent 1?
22. Analytical techniques  →  22.2. Mass spectrometry
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For Examiner’s Use The physical properties of polymers depend on the average relative molecular mass of the polymer chains and on the functional groups present in the monomers. The presence of side-chains in addition polymers can increase the spacing between polymer chains in the bulk substance and hence reduce the overall density. In condensation polymers it is the nature of the side-chain that is often more important since this can lead to cross-linking of the polymer chains forming a three-dimensional structure. For each of the following polymers, give the structure of the monomerand state the type of reaction used to produce the polymer. N H polymer A (CH2)6 (CH2)4 N H C O C O n monomertype of reaction polymer B H C H C CH3 H C H H C CH3 H n monomertype of reaction N H polymer C (CH2)5 C O n monomertype of reaction For Examiner’s Use Look at the structures of the three polymers and answer the following questions. Suggest why the density of B is lower than that of A. Which polymer will have the weakest forces between chains, and what is the nature of these forces?
20. Polymerisation  →  20.1. Addition polymerisation
14. Hydrocarbons  →  14.2. Alkenes
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