9701_s22_qp_43
A paper of Chemistry, 9701
Questions:
7
Year:
2022
Paper:
4
Variant:
3
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The solubility of the Group2 sulfates decreases down the group. Explain this trend. Describe what is observed when magnesium and barium are reacted separately with an excess of dilute sulfuricacid. magnesium barium  The solubility product, Ksp, of BaSO4 is 1.08×10–10 mol2 dm–6 at 298 K. Calculate the solubility of BaSO4 in g per 100 cm3 of solution.  solubility of BaSO4 = g per 100 cm3 of solution  The equation for the formation of a gaseous sulfate ion is shown. S+ 2O2+ 2e– → SO4 2–∆H = of SO4 2–Calculate the standard enthalpy change of formation, , of SO4 2–. It may be helpful to draw a labelled energy cycle. Use relevant data from Table1.1 in your calculations. Table 1.1 energy change value / kJ mol–1 lattice energy of barium sulfate, BaSO4–2469 standard enthalpy change of formation of barium sulfate –1473 standard enthalpy change of atomisation of barium +180 first ionisation energy of barium +503 second ionisation energy of barium +965 standard enthalpy change of atomisation of sulfur +279 standard enthalpy change for S→ S2–+440 standard enthalpy change for O→ O2–+657 O=O bond energy +496  of SO4 2–= kJ mol–1 Suggest how the lattice energy of BaSO4differs from the lattice energy of Cs2SO4. Explain your answer. The reaction of solid hydrated barium hydroxide, Ba(OH)2•8H2O, with ammonium salts is endothermic. Calculate the minimum temperature at which the reaction of Ba(OH)2•8H2O with NH4NO3 becomes feasible. Show all your working. Ba(OH)2•8H2O+ 2NH4NO3→ 2NH3+ Ba(NO3)2+ 10H2O= +132 kJ mol–1 ∆S o = +616 J K–1 mol–1  temperature = °C Bariumhydroxide reacts readily with ammoniumchloride on mixing at room temperature. Ba(OH)2•8H2O+ 2NH4Cl → 2NH3+ BaCl 2•2H2O+ 8H2O = +133 kJ mol–1 Some relevant standard entropies are given in Table 1.2. Table 1.2 substance Ba(OH)2•8H2ONH4Cl NH3BaCl 2•2H2OH2OS o / J K–1 mol–1 Calculate the standard Gibbs free energy change, ∆G o, for this reaction at 25 °C. ∆G o = kJ mol–1 
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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Define transition element. Sketch the shape of a 3dz2 orbital. z x y  Manganese(oxide, MnO2, acts as a heterogeneous catalyst in the decomposition of hydrogenperoxide, H2O2. Explain what is meant by a heterogeneous catalyst. Describe the mode of action of a heterogeneous catalyst in a reaction. Manganese(oxide, Mn2O7, can be made by treatment of KMnO4 with concentrated sulfuricacid (reaction 1). Mn2O7 readily decomposes at room temperature to form manganese(oxide and a colourless diatomic gas (reaction 2). Construct equations for both the reactions described. reaction 1 reaction 2  Aqueous manganese(ions show similar chemical properties to aqueous copper(ions when reacted separately with NaOHand with concentrated HCl. Write the ionic equation, and state the type of reaction, for the reaction of [Mn(H2O)6]2+ with NaOH. ionic equation type of reaction  Write the ionic equation, and state the type of reaction, for the reaction of [Mn(H2O)6]2+ with concentrated HCl. ionic equation type of reaction  Table2.1 lists relevant electrode potentials for some electrode reactions. Table 2.1 electrode reaction E o / V Mn2+ + 2e– Mn –1.18 Cl 2 + 2e– 2Cl – +1.36 2HOCl + 2H+ + 2e– Cl 2 + 2H2O +1.64 MnO2 + 4H+ + 2e– Mn2+ + 2H2O +1.23 MnO4 – + 4H+ + 3e– MnO2 + 2H2O +1.67 Suggest the formula of the manganese species formed when Mn2+reacts with Cl 2. State the type of reaction. formula of manganese species formed type of reaction  
8. Reaction kinetics  →  8.3. Homogeneous and heterogeneous catalysts
2. Atoms, molecules and stoichiometry  →  2.3. Formulas
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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The rate of reaction between 2-chloro-2-methylpropane, (CH3)3CCl, and methanol is investigated. When a large excess of methanol is used, the overall reaction is first order. (CH3)3CCl + CH3OH → (CH3)3COCH3 + HCl Fig.3.1 shows the results obtained. 0.0200 0.0175 0.0150 0.0125 0.0100 0.0075 0.0050 0.0025 0.0000 time / s [(CH3)3CCl ] / mol dm–3 Use the graph to determine the rate of reaction at 40 s. Show all your working.  rate = mol dm–3 s–1 Use the graph to show that the overall reaction is first order. Explain your answer. In a different reaction, which is also a first order reaction, 75% of the reactant is consumed in 320 s. Calculate the rate constant, k, for this reaction. State the units for k.  k = units = Define standard electrode potential, E o. A salt bridge is used in an electrochemical cell. State the function of the salt bridge. Explain your answer. Complete the diagram of the apparatus that can be used to measure the E o of the Cr2O7 2–, H+/Cr3+electrode against the standard hydrogen electrode. Your diagram should be fully labelled to identify all apparatus, substances and conditions. salt bridge  The E o of the Cr2O7 2–, H+/Cr3+electrode is +1.33 V. Label the negative electrode and the direction of electron flow in the external circuit when the current flows in your diagram in . Table3.1 lists relevant electrode potentials for some electrode reactions for use in and . Table 3.1 electrode reaction E o / V Cr2O7 2– + 14H+ + 6e– 2Cr3+ + 7H2O +1.33 CH3CHO + 2H+ + 2e– CH3CH2OH –0.61 CH3COOH + 2H+ + 2e– CH3CHO + H2O –0.94 O2 + 4H+ + 4e– 2H2O +1.23 Ethanal is oxidised to ethanoic acid in the presence of Cr2O7 2– ions. Construct the ionic equation for the oxidation of ethanal to ethanoic acid using dichromate(in acid conditions. Calculate the for this reaction. ionic equation  = V  In an ethanol-oxygen fuel cell, CH3CH2OHand O2are in contact with two inert electrodes immersed in an acidic solution. The cell reaction for the oxidation of ethanol by oxygen is shown. 2CH3CH2OH + O2 → 2CH3COOH + 2H2O = +2.01 V Calculate ∆G o, in kJ mol–1, for the oxidation of ethanol by oxygen. ∆G o = kJ mol–1 
11. Group 17  →  11.4. The reactions of chlorine
8. Reaction kinetics  →  8.1. Rate of reaction
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The 3d orbitals in an isolated Fe2+ ion are degenerate. Complete the diagram to show the splitting of the 3d orbital energy levels in an isolated Fe2+ ion and when Fe2+ forms an octahedral complex. energy Fe2+ in an octahedral complex isolated Fe2+ ion  Bipyridine, bipy, is a bidentate ligand. N N bipy Explain what is meant by bidentate ligand. The complex [Fe3]2+ exists as two stereoisomers. Complete the three-dimensional diagrams to show the two stereoisomers of [Fe3]2+. State the type of stereoisomerism shown. Use N N to represent bipy in your diagrams. Fe Fe type of stereoisomerism  Standard electrode potentials can be used to compare the stability of different complex ions for a given transition element. Table 4.1 lists electrode potentials for some electrode reactions for Fe3+ / Fe2+ systems. Table 4.1 electrode reaction E o / V [Fe(H2O)6]3+ + e– [Fe(H2O)6]2+ +0.77 [Fe(CN)6]3– + e– [Fe(CN)6]4– +0.36 [Fe3]3+ + e– [Fe3]2+ +0.96 Use relevant data from Table 4.1 to state which iron(complex is hardest to reduce. Explain your choice. iron(complex explanation  The ligand bipyridine consists of two pyridine rings. Pyridine, C5H5N, and benzene, C6H6, have similar planar, cyclic structures. N pyridine By reference to the hybridisation of the carbon atoms and the nitrogen atom, and orbital overlap, suggest how the σ and π bonds are formed in a pyridine molecule. Pyridine reacts with Cl 2 in the presence of Al Cl 3 as shown in . N pyridine N 3-chloropyridine + Cl 2 + HCl Al Cl 3 Cl The mechanism of this reaction is similar to that of the chlorination of benzene. Al Cl 3 reacts with chlorine to generate an electrophile, Cl +. Complete the diagram to show the mechanism for the reaction of pyridine with Cl +. Include all relevant charges, dipoles, lone pairs of electrons and curly arrows as appropriate. N Cl +  
3. Chemical bonding  →  3.4. Covalent bonding and coordinate (dative covalent) bonding
1. Atomic structure  →  1.3. Electrons, energy levels and atomic orbitals
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Compare the relative acidities of benzoic acid (C6H5COOH), phenylmethanol (C6H5CH2OH), and phenol (C6H5OH). Explain your reasoning. > > most acidic least acidic  A series of nine separate experiments is carried out as shown in Table5.1. Complete the table by placing a tick (✓) in the relevant box if a reaction occurs. Place a cross (✗) in the box if no reaction occurs. Table 5.1 benzoic acid phenylmethanol phenol NaNaOHNa2CO3 Benzoyl chloride, C6H5COCl, can be synthesised by the reaction of benzoic acid with either PCl 5 or SOCl 2. Complete the equations for these reactions. reaction 1 C6H5COOH + PCl 5 → C6H5COCl + + reaction 2 C6H5COOH + SOCl 2 → C6H5COCl + +  Use your answer to to suggest why it is easier to isolate, in a pure form, the C6H5COCl from reaction2 compared to reaction1. Benzoyl chloride is hydrolysed by water at room temperature to form benzoic acid. Complete the diagram to show the mechanism for the reaction between C6H5COCl and H2O. Include charges, dipoles, lone pairs of electrons and curly arrows as appropriate. Cl products C O H2O  Name the type of mechanism you showed in . Acyl chlorides react with sodium carboxylates to form acid anhydrides as shown in Fig.5.1. C + O acyl chloride R Cl C + NaCl O acid anhydride O R' R C O C O sodium carboxylate R' ONa The condensation polymers, polyanhydride and polyester, are formed by similar methods. The repeat unit for a polyanhydride is shown in Fig.5.2. polyanhydride C O O CH2 CH2 CH2 CH2 CH2 CH2 O O C O O C O C O Use Fig.5.1 and Fig.5.2 to suggest the structures of the two monomers used to make this polyanhydride.  Polyanhydrides are biodegradable polymers. Suggest how this polyanhydride can be degraded. 
18. Carboxylic acids and derivatives  →  18.1. Carboxylic acids
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
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Describe what is meant by a racemic mixture. Asparagine is an amino acid that contains a chiral carbon atom and displays stereoisomerism. Separate samples of asparagine are dissolved in CDCl 3 and analysed using carbon‑13 and proton (1H) NMR spectroscopy. C C asparagine H2N CH2 NH2 H O OH O C Predict the number of peaks seen in the carbon‑13 and proton (1H) NMR spectra of asparagine. carbon‑13 NMR proton (1H) NMR number of peaks  The isoelectric point of asparagine, asn, is at pH5.4. Describe the meaning of the term isoelectric point. Draw the structure of asparagine at pH1.0.  Asparagine can polymerise to form poly. Draw the structure of poly, showing two repeat units. The peptide linkage should be shown displayed.  The isoelectric point of lysine, lys, is at pH9.8. H2N C lysine H (CH2)4 NH2 COOH A mixture of the dipeptide lys-asn and its two constituent amino acids, asparagine and lysine, is analysed by electrophoresis using a buffer at pH 5.0. The results obtained are shown in Fig.6.3. mixture applied here E F G + – Suggest identities for the species responsible for spots E, F and G. Explain your answers. spot identity E F G  Thin-layer and gas-liquid chromatography can be used to analyse mixtures of substances. Each type of chromatography makes use of a stationary phase and a mobile phase. Complete Table6.1 with an example of each of these. Table 6.1 stationary phase mobile phase thin-layer chromatography gas-liquid chromatography  An unknown amino acid is analysed using thin-layer chromatography. Two chromatographs of the unknown amino acid and four reference amino acids, P, Q, R and S, are obtained using two different solvents. P unknown amino acid solvent 1 Q R S P unknown amino acid solvent 2 Q R S cm Identify the unknown amino acid. Justify your answer. A mixture containing three organic compounds is analysed by gas chromatography and mass spectrometry. The gas chromatogram is shown. peak area / mm2 J J K K L L retention time / minutes The area underneath each peak is proportional to the mass of the respective compound in the mixture. The concentration of K in the mixture is 5.52×10–2 g dm–3. Calculate the concentration, in mol dm–3, of compound L in the mixture. [Mr: L, 116]  concentration of L = mol dm–3 
22. Analytical techniques  →  22.2. Mass spectrometry
17. Carbonyl compounds  →  17.1. Aldehydes and ketones
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
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Procaine is used as an anaesthetic in medicine. It can be synthesised from methylbenzene in fivesteps as shown in Fig.7.1. CH3 methylbenzene COOH NO2 COCl NO2 C O O CH2CH2N(CH2CH3)2 NO2 X steps 1 and 2 step 3 step 5 step 4 SOCl 2 C procaine O O CH2CH2N(CH2CH3)2 NH2 Name all the functional groups present in procaine. A molecule of procaine has 13 carbon atoms. State the number of carbon atoms that are sp, sp2 and sp3 hybridised in procaine. sp carbons = sp2 carbons = sp3 carbons =  The proton (1H) NMR spectrum of procaine dissolved in D2O is recorded. Predict the number of peaks observed. State why procaine can act as a base. CompoundX can be synthesised in two steps from methylbenzene. CH3 methylbenzene COOH NO2 X W step 1 step 2 Draw the structure of compoundW in the box provided. State the reagents and conditions for step1 and step2. step 1 step 2  Procaine is synthesised in three steps from X. Suggest the reagents and conditions for step4 and for step5 in . step 4 step 5  Explain what is meant by partition coefficient, Kpc. The partition coefficient of procaine between octan-1-ol and water is 1.77. Octan-1-ol and water are immiscible. A solution containing 0.500 g of procaine in 75.0 cm3 of water is shaken with 50.0 cm3 of octan‑1‑ol. Calculate the mass of procaine that is extracted into the octan‑1‑ol.  mass of procaine extracted = g 
22. Analytical techniques  →  22.2. Mass spectrometry
21. Organic synthesis  →  21.1. Organic synthesis
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