9701_m22_qp_42
A paper of Chemistry, 9701
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6
Year:
2022
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4
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2
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Iodine is found naturally in compounds in many different oxidation states. Iodide ions, I–, react with acidified H2O2to form iodine, I2, and water. This reaction mixture is shaken with cyclohexane, C6H12, to extract the I2. Cyclohexane is immiscible with water. Identify the role of H2O2in its reaction with I– ions in acidic conditions. Write an ionic equation for the reaction. role ionic equation  15.0 cm3 of C6H12 is shaken with 20.0 cm3 of an aqueous solution containing I2 until no further change is seen. It is found that 0.390 g of I2 is extracted into the C6H12. The partition coefficient of I2 between C6H12 and water, Kpc, is 93.8. Calculate the mass of I2 that remains in the aqueous layer. Show your working.  mass of I2 in aqueous layer = g Suggest how the value of Kpc of I2 between hexan-2-one, CH3(CH2)3COCH3, and water compares to the value given in . Explain your answer. The Group1 iodides all form stable ionic lattices and are soluble in water. Define enthalpy change of solution. Use the data in Table1.1 to calculate the enthalpy change of solution of potassiumiodide, KI. Table 1.1 process enthalpy change, ∆H / kJ mol–1 K++ I–→ KI–629 K+→ K+–322 I–→ I––293  enthalpy change of solution = kJ mol–1 Suggest the trend in the magnitude of the lattice energies of the Group1 iodides, LiI, NaI, KI. Explain your answer. The concentration of Cu2+in a solution can be determined by the reaction of Cu2+ ions with I– ions. reaction 1 2Cu2+ + 4I– → 2CuI + I2 The I2 produced in reaction1 is titrated against a solution containing thiosulfate ions, S2O3 2–, using a suitable indicator. reaction 2 2S2O3 2– + I2 → S4O6 2– + 2I– A 25.0 cm3 portion of a Cu2+solution reacts with an excess of I–. The end-point of the titration occurs when 22.30 cm3 of 0.150 mol dm–3 S2O3 2–is added. Calculate the concentration of Cu2+in the original solution.  concentration of Cu2+= mol dm–3 Identify a suitable indicator for the titration. Copper(and copper(both contain electrons in all five 3d orbitals. Sketch the shape of a 3dxy orbital on the axes provided. z y x  The reaction of I– ions with persulfate ions, S2O8 2–, can be catalysed by Fe3+ ions. 2I– + S2O8 2– → I2 + 2SO4 2– Write equations to show how Fe3+ catalyses this reaction. An orange precipitate of HgI2 forms when Hg2+ ions are added to KI. The solubility of HgI2 at 25 °C is 1.00 × 10–7 g dm–3. Calculate the solubility product, Ksp, of HgI2. Include units in your answer. [Mr: HgI2, 454.4]  value of Ksp =  units =  
11. Group 17  →  11.3. Some reactions of the halide ions
2. Atoms, molecules and stoichiometry  →  2.3. Formulas
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Silicon is the second most abundant element by mass in the Earth’s crust. In industry, silicon is extracted from SiO2 by reaction with carbon at over 2000 °C. reaction 1 SiO2+ 2C→ Si+ 2COExplain why the entropy change, ∆S, of reaction1 is positive. Reaction1 is highly endothermic. Suggest the effect of an increase in temperature on the feasibility of this reaction. Explain your answer. Silicon is purified by first heating it in a stream of HCl to form SiHCl 3. The SiHCl 3 formed is then distilled to remove other impurities. reaction 2 Si+ 3HCl → SiHCl 3+ H2Table2.1 shows some standard entropy data. Table 2.1 compound standard entropy, S o / J K–1 mol–1 Si19 HCl 187 SiHCl 3314 H2131 Use the data in Table2.1 to calculate ∆S o for reaction2.  ∆S o = J K–1 mol–1 Reaction3 is the reverse of reaction2 and is used to obtain pure silicon. reaction 3 SiHCl 3+ H2→ Si+ 3HCl ∆H = +219.3 kJ mol–1 Use this information and your answer to to calculate the temperature, in K, at which reaction3 becomes feasible. Show your working. [If you were unable to answer , you should use ∆S o = –150 J K–1 mol–1 for reaction2. This is not the correct answer to .]  temperature = K Silicon can also be produced by electrolysis of SiO2 dissolved in molten CaCl 2. The relevant half-equation for the cathode is shown. SiO2 + 4e– → Si + 2O2– Calculate the time, in seconds, required to produce 1.00 g of Si by this electrolysis, using a current of 6.00 A. Assume no other substances are produced at the cathode.  time = s 
5. Chemical energetics  →  5.1. Enthalpy change, \(\Delta H\)
8. Reaction kinetics  →  8.2. Effect of temperature on reaction rates and the concept of activation energy
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Titanium is a transition element in Period4. It is commonly found as TiO2 in minerals. Define transition element. Identify two typical properties of transition elements.  The TiO2+ ion forms when TiO2 reacts with an excess of sulfuric acid. TiO2+ can be reduced by zinc metal in acidic conditions to form a purple solution containing Ti3+. TiO2+is a colourless ion. Suggest why. Give the electronic configuration of an isolated Ti3+ ion. 1s2 ��������������������������������������������������������������������������������������������������������������������������������� Write an ionic equation for the reduction of TiO2+ by zinc metal in acidic conditions. Acidified Ti3+reacts with oxygen dissolved in water as shown. 4Ti3+ + O2 + 2H2O → 4TiO2+ + 4H+ ∆G o = –436.1 kJ mol–1 The standard reduction potential, E o, of O2 + 4H+ + 4e– 2H2O is +1.23 V. Calculate the standard reduction potential, E o, in V, of the TiO2+/ Ti3+half-cell. Show your working.  E o = V When aqueous citrate ions, C6H5O7 3–, are added to Ti3+, the [Ti(C6H5O7)2]3–complex forms. Explain, in terms of d-orbitals, why Ti3+ is able to form complex ions. Acidified [Ti(C6H5O7)2]3–does not react with oxygen dissolved in water, unlike acidified Ti3+. Suggest what this means for the value of the standard reduction potential, E o, of the following half‑cell. [Ti(C6H5O7)2]2–+ e– [Ti(C6H5O7)2]3–Explain your answer. Some reactions of TiO2 are shown in Fig.3.1. The anion, acac–, is a bidentate ligand. TiO2 TiF6 2– HF Cl 2 TiCl 4 Ti2Cl 2 acac– The titanium ions in TiF6 2– and Ti2Cl 2 have a coordination number of 6. State what is meant by coordination number. Write an equation for the formation of TiF6 2– from TiO2. State what is meant by bidentate ligand. Ti2Cl 2 shows both optical and geometrical (cis/trans) isomerism. Ti2Cl 2 exists as three stereoisomers. The structure of one stereoisomer of Ti2Cl 2 is shown in Fig.3.2. acac acac Ti stereoisomer 1 Cl Cl Complete the structures of the other two stereoisomers of Ti2Cl 2. stereoisomer 2 Ti stereoisomer 3 Ti  The acac– anion is symmetrical. Deduce which, if any, of stereoisomers 1, 2 and 3 in are polar. Explain your answer. 
9. The Periodic Table: chemical periodicity  →  9.2. Periodicity of chemical properties of the elements in Period 3
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Compounds F and J are shown in Fig.4.1. F O OH H2N J O O OH F and J both contain the arene functional group. Identify the other functional groups in F and J. F: J:  State the number of chiral centres in a molecule of F and in a molecule of J. number of chiral centres in: F = J =  A student proposes a multi-step synthesis of F from benzene, as shown in Table 4.1. Complete Table4.1 by providing relevant details of the reagents and conditions for steps1 and 4, and the structure of product D. Table 4.1 F COOH H2N E COOH O2N COOH O2N D D organic reactant step reagentand conditions concentrated HNO3 and concentrated H2SO4 hot alkaline KMnO4 then dilute H2SO4 organic product  In a second multi-step synthesis, the student changes the order in which the reagents and conditions are used. The reaction scheme is shown in Fig.4.2. G is the major product of this synthesis. concentrated HNO3 and concentrated H2SO4 COOH hot alkaline KMnO4 then dilute H2SO4 step 1 G Draw the structure of G. Explain why G is the major product of the synthesis rather than E.  J reacts under suitable conditions with NaOH. After acidification of the reaction mixture, compounds K and L form. J O O OH K O OH + L OH 1. NaOH2. HCl Give the molecular formula of L. State the two types of reaction that occur when J reacts with NaOH.  K can also be synthesised from phenol, C6H5OH. Fig.4.4 shows several reactions of phenol. K N M phenol O OH OH OH NaOHfollowed by CO2and H2SO4 reaction 3 excess Br2reaction 2 reaction 1 NaWrite an equation for the formation of M in reaction1. Draw N, the product of reaction2.  Explain why phenol is a weaker acid than K. Phenol and benzene both react with nitric acid, as shown in Fig.4.5. OH OH NO2 dilute HNO3 NO2 concentrated HNO3 concentrated H2SO4 Explain why the reagents and conditions for these two reactions are different. 
21. Organic synthesis  →  21.1. Organic synthesis
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2-Chloropropanoic acid, CH3CHCl COOH, is used in many chemical syntheses. An equilibrium is set up when CH3CHCl COOH is added to water. Write the equation for this equilibrium. 0.150 mol of CH3CHCl COOH dissolves in 250 cm3 of distilled water to produce a solution of pH1.51. Calculate the pKa of CH3CHCl COOH.  pKa = An equal concentration of aqueous propanoic acid has pH2.55. Explain the difference in the pH of solutions of equal concentration of CH3CHCl COOH and propanoic acid. When CH3CHCl COOH reacts with aqueous NH3, alanine forms. alanine C H CH3 H2N COOH Alanine is an amino acid. Its isoelectric point is 6.1. State what is meant by isoelectric point. Give the structural formula of alanine at pH 2. Alanine exists as a pair of optical isomers. The structure of one optical isomer is shown in Fig.5.2. Draw the three-dimensional structure of the other optical isomer of alanine. optical isomer 1 C CH3 COOH H H2N optical isomer 2  Polymer C forms from the reaction between alanine and 4-aminobutanoic acid, H2N(CH2)3COOH. Draw a repeat unit of C. The functional group formed should be displayed.  State the type of polymerisation shown in . Scientists are investigating C as a replacement for polyin packaging. Suggest an advantage of using C instead of poly. A student studies the reaction of CH3CHCl COOH with aqueous NH3 to determine the reaction mechanism. The student finds that when CH3CHCl COOH and NH3 are added in a 1 : 1 stoichiometric ratio, the conjugate acid and base of the reactants are quickly formed. reaction 1 CH3CHCl COOH + NH3 → CH3CHCl COO– + NH4 + Identify the conjugate acid–base pairs in reaction1. conjugate acid–base pair I and conjugate acid–base pair II and  In an excess of NH3, CH3CHCl COO– undergoes a nucleophilic substitution reaction. reaction 2 CH3CHCl COO– + NH3 → CH3CH(NH2)COO– + H+ + Cl – A student investigates the rate of reaction2. The student mixes CH3CHCl COO– with a large excess of NH3. The graph in Fig.5.3 shows the results obtained. time / s 1000 1200 1400 1600 0.0250 0.0200 0.0150 0.0100 0.0050 0.0000 [CH3CHCl COO–] / mol dm–3 Use the graph in Fig.5.3 to show that reaction2 is first order with respect to [CH3CHCl COO–]. Explain why a large excess of NH3 needs to be used in order to obtain the results in Fig.5.3. The student measures the effect of changing the concentration of NH3 on the rate of reaction2. Table5.1 shows the results obtained. Table 5.1 experiment [CH3CHCl COO–] / mol dm–3 [NH3] / mol dm–3 initial rate of reaction / mol dm–3 s–1 0.00120 0.00300 1.47 × 10–5 0.00120 0.00450 2.21 × 10–5 Use the information in Table 5.1 and in to determine whether the nucleophilic substitution reaction proceeds via an SN1 or an SN2 mechanism. Explain your answer. Describe the effect of an increase in temperature on the rate of reaction of CH3CHCl COO– and NH3. Explain your answer. When an excess of CH3CHCl COO– is used, further substitution reactions occur. One product has the formula C6H9NO4 2–. Suggest the structure of C6H9NO4 2–.  
14. Hydrocarbons  →  14.2. Alkenes
11. Group 17  →  11.4. The reactions of chlorine
15. Halogen compounds  →  15.1. Halogenoalkanes
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Lidocaine is used as an anaesthetic. A synthesis of lidocaine is shown in Fig.6.1. X Y NH2 HN W O + Cl Cl O Cl HN O lidocaine N(C2H5)2 reaction 1 reaction 2 (C2H5)2NH W can be formed by reacting HOCH2COOH with an excess of SOCl 2. Write an equation for this reaction. After W and X have reacted together, an excess of CH3COONais added to the reaction mixture. Suggest why. The reaction of W with X, reaction 1, follows an addition–elimination mechanism. Complete the mechanism for the reaction of W with X. Include all relevant curly arrows, lone pairs of electrons, charges and partial charges. Use Ar–NH2 to represent X. O Ar NH2 Cl Cl  (C2H5)2NH reacts with Y in reaction2. Explain why (C2H5)2NH can act as a nucleophile. The purity of lidocaine can be checked using thin-layer chromatography. Ethyl ethanoate is used as the solvent. The Rf values of X and lidocaine are given in Table6.1. Table 6.1 compound Rf X 0.49 lidocaine 0.71 Identify the substances used as the mobile and stationary phases in this thin‑layer chromatography experiment. mobile phase stationary phase  Describe how an Rf value can be calculated. Suggest why the Rf value for X is less than that for lidocaine. The proton (1H) NMR spectrum of lidocaine is shown in Fig.6.2. HN O lidocaine N(C2H5)2 chemical shift / ppm 8.9 7.1 3.0 2.6 1.1 2.3 Table 6.2 environment of proton example chemical shift range δ / ppm alkane –CH3, –CH2–, >CH– 0.9–1.7 alkyl next to C=O CH3–C=O, –CH2–C=O, >CH–C=O 2.2–3.0 alkyl next to aromatic ring CH3–Ar, –CH2–Ar, >CH–Ar 2.3–3.0 alkyl next to electronegative atom CH3–O, –CH2–O, –CH2–Cl 3.2–4.0 attached to alkene =CHR 4.5–6.0 attached to aromatic ring H–Ar 6.0–9.0 aldehyde HCOR 9.3–10.5 alcohol ROH 0.5–6.0 phenol Ar–OH 4.5–7.0 carboxylic acid RCOOH 9.0–13.0 alkyl amine R–NH– 1.0–5.0 aryl amine Ar–NH2 3.0–6.0 amide RCONHR 5.0–12.0 Name the splitting patterns at δ 2.6 and δ 1.1. δ 2.6 δ 1.1  The relative peak area of the peaks at δ 3.0 and δ 2.3 is 1 : 3 respectively. Identify the protons in the 1H NMR spectrum of lidocaine that are responsible for the peaks at the following chemical shift values. δ 7.1 δ 3.0 δ 2.3  Predict the number of peaks in the carbon‑13 (13C) NMR spectrum of lidocaine. 
17. Carbonyl compounds  →  17.1. Aldehydes and ketones
15. Halogen compounds  →  15.1. Halogenoalkanes
11. Group 17  →  11.4. The reactions of chlorine
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