9701_w21_qp_43
A paper of Chemistry, 9701
Questions:
10
Year:
2021
Paper:
4
Variant:
3
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1
When dilute sulfuricacid is electrolysed, water is split into hydrogen and oxygen. 2H2O→ 2H2+ O2A current of x A is passed through the solution for 14.0minutes. 462 cm3 of hydrogen are produced at the cathode, measured under room conditions. Calculate the number of hydrogen molecules produced during the electrolysis.  number of hydrogen molecules = Calculate the total number of electrons transferred to produce this number of hydrogen molecules.  total number of electrons = Calculate the quantity of charge, in coulombs, of the total number of electrons calculated in .  quantity of charge = C Calculate the current, x, passed during this experiment.  x = A The standard entropies, S o, of three species are given in the table. species S o / J K–1 mol–1 H2O+70 H2+131 O2+205 Calculate ∆S o for the reaction 2H2O→ 2H2+ O2. ∆S o = J K–1 mol–1 ∆H o for the reaction 2H2O→ 2H2+ O2is +572 kJ mol–1. Calculate ∆G o for this reaction at 298 K. ∆G o = kJ mol–1 Predict the effect of increasing temperature on the spontaneity of this reaction. Explain your answer.
11. Group 17  →  11.4. The reactions of chlorine
14. Hydrocarbons  →  14.2. Alkenes
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2
Solution Y is hydrochloric acid, HCl . Solution Z is aqueous 4-chlorobutanoic acid, Cl (CH2)3CO2H. The pKa of Cl (CH2)3CO2His 4.52. The pH of both solutions is 4.00. Write an expression for the Ka of Cl (CH2)3CO2H. Ka =  Write a mathematical expression to describe the relationship between Ka and pKa. Calculate [H+] in solutions Y and Z.  [H+] = mol dm–3 Calculate the ratio [HCl ] dissolved in solution Y [Cl (CH2)3CO2H] dissolved in solution Z .  [HCl ] dissolved in solution Y [Cl (CH2)3CO2H] dissolved in solution Z = A buffer solution of pH5.00 is produced by adding sodiumpropanoate to 5.00 g of propanoicacid in 100 cm3 of distilledwater. Calculate the mass of sodiumpropanoate that must be used to produce this buffer solution. The Ka of propanoicacid is 1.35 × 10–5 mol dm–3. [Mr: propanoic acid, 74.0; sodium propanoate, 96.0]  mass of sodium propanoate = g Some dilute sulfuricacid is mixed with a small sample of the buffer solution described in . The final pH of the mixture is close to 1. Explain this observation.
11. Group 17  →  11.4. The reactions of chlorine
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
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3
Define the term electron affinity. Write an equation for the process corresponding to the second ionisation energy of calcium. Include state symbols. Some data relating to calcium and oxygen are listed. Select relevant data from this list for your answers to parts , and . process value / kJ mol–1 first ionisation energy of oxygen +1310 second ionisation energy of oxygen +3390 first electron affinity of oxygen –142 second electron affinity of oxygen +844 enthalpy change for 1 2O2+ 2e– → O2–+951 enthalpy change for Ca→ Ca2++ 2e– +1933 lattice energy of CaO–3517 Oxygen exists as O2 molecules. Use the data in this question to calculate a value for the bond energy of the O=O bond. Show all your working.  bond energy = kJ mol–1 Suggest why the first electron affinity of oxygen is negative. Suggest why the second electron affinity of oxygen is positive. Calculate the enthalpy of formation of calciumoxide, CaO.  enthalpy of formation = kJ mol–1 The lattice energy of lithiumfluoride, LiF, is –1022 kJ mol–1. Identify the factor that causes the lattice energy of calciumoxide to be more exothermic than that of lithiumfluoride. Explain why this factor causes the difference in lattice energies.
1. Atomic structure  →  1.4. Ionisation energy
3. Chemical bonding  →  3.4. Covalent bonding and coordinate (dative covalent) bonding
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4
Separate samples of 0.02 mol of calciumcarbonate and 0.02 mol of bariumcarbonate are heated until completely decomposed to the metal oxide and carbondioxide. State which of these two Group2 carbonates requires the higher temperature before it begins to decompose. Explain your answer. After decomposition is complete, the 0.02 mol sample of calciumoxide is taken and added to 2.00 dm3 of water. A solution is formed with no solid present. Dilute sulfuricacid is then added dropwise until a precipitate is seen. The same procedure is repeated with the 0.02 mol sample of bariumoxide, using the same concentration solution of dilute sulfuricacid. Identify the sample to which most sulfuricacid must be added to cause a precipitate to appear. Explain your answer. You should refer to the solubilities of the precipitates and relevant energy terms in your answer. Calculate the mass, in g, of CO2 produced by the decomposition of 0.020 moles of calciumcarbonate.  mass of CO2 = g Calculate the minimum mass, in g, of propane that would, on complete combustion, produce the same mass of CO2 calculated in . Give your answer to three significant figures.  mass of propane = g
2. Atoms, molecules and stoichiometry  →  2.4. Reacting masses and volumes (of solutions and gases)
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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5
[MnCl 4]2– is a complex ion. Deduce the oxidation state of manganese in [MnCl 4]2–.  oxidation state = The [MnCl 4]2– complex does not contain any 180° bond angles. Draw a three-dimensional diagram to show the shape of the [MnCl 4]2– complex. State one bond angle on your diagram. Mn  A solution of cobalt(sulfate contains the complex ion [Co(H2O)6]2+. A solution containing [Co(H2O)6]2+ is reacted separately with an excess of each of NaOH, NH3and NaCl . Write an equation for each of these reactions. State one observation that can be made immediately after the reaction, include the colour and state of the cobalt-containing product. [Co(H2O)6]2+ and an excess of NaOHequation observation  [Co(H2O)6]2+ and an excess of NH3equation observation  [Co(H2O)6]2+ and an excess of NaCl equation observation  Name the type of reaction that occurs in . Cobalt forms the complex ion [Co(NH3)22]2+. The abbreviation en is used for the bidentate ligand 1,2-diaminoethane, H2NCH2CH2NH2. The complex ion shows both geometrical and optical isomerism. Define the term bidentate ligand. Draw three-dimensional diagrams for the two optical isomers of [Co(NH3)22]2+. Each en ligand can be represented using N N . Co Co  
2. Atoms, molecules and stoichiometry  →  2.3. Formulas
17. Carbonyl compounds  →  17.1. Aldehydes and ketones
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6
An excess of sodiumiodide is added to a solution of copper(sulfate. Iodine and a white precipitate of copper(iodide are formed. Write an equation for the reaction that occurs. Explain why the copper(sulfate solution is coloured. Suggest why the precipitate of copper(iodide is white. Use suitable E o values from the Data Booklet to predict whether iodide ions can reduce Cu2+ to Cu+ under standard conditions. Explain your answer. An excess of sodiumiodide is added to copper(sulfate solution. Copper(iodide forms as a precipitate. After precipitation, [Cu+] is much lower than 1.0 mol dm–3. Use this information and your answer to to explain how the relevant electrode potentials change and hence why I– ions can reduce Cu2+ ions. 
11. Group 17  →  11.3. Some reactions of the halide ions
2. Atoms, molecules and stoichiometry  →  2.3. Formulas
11. Group 17  →  11.4. The reactions of chlorine
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7
The structure of phenylethanoicacid is shown. O OH Give the number of different peaks in the carbon-13 (13C) NMR spectrum of phenylethanoic acid.  number of peaks = Phenylethanoicacid, ethanol and phenol can all behave as acids. Compare and explain the relative acidities of these three compounds. > > most acidic least acidic Phenylethanoicacid can be synthesised using benzene as the starting material. In the first stage of this synthesis, benzene reacts with chloromethane in the presence of an Al Cl 3 catalyst to form methylbenzene. Chloromethane reacts with Al Cl 3 to form two ions. One of these is the carbocation +CH3. Write an equation for the reaction between chloromethane and Al Cl 3. Draw the mechanism of the reaction between benzene and +CH3. Include all relevant curly arrows, charges and the structure of the intermediate. intermediate CH3 +CH3  A three-step synthesis of phenylethanoicacid from methylbenzene is shown. step 1 step 2 compound Q step 3 Br O OH State reagents and conditions for step1. Suggest the structure of compoundQ.  State reagents and conditions for steps 2 and 3. step 2 step 3  Draw the structure of an organic by-product that forms in step 1.  
21. Organic synthesis  →  21.1. Organic synthesis
17. Carbonyl compounds  →  17.1. Aldehydes and ketones
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9
CompoundT is made by a three-stage synthesis. In stage1, phenylethanoicacid reacts with a suitable reagent to form compoundR. O OH O Cl phenylethanoic acid R stage 1 Suggest a suitable reagent for stage1. In stage 2, compoundR reacts with ethylamine to form compoundS. + C2H5NH2 O Cl R O S stage 2 N H Name the functional group formed in stage2. Identify the other product formed in stage2. In stage3, compoundS reacts with a suitable reagent to form compoundT. O S stage 3 N H T N H State the formula of a suitable reagent for stage3. Name the type of reaction that occurs in stage3. The relative abundance of the molecular ion peak in the mass spectrum of ethylamine is 62. Calculate the relative abundance of the M+1 peak in the mass spectrum of ethylamine.  relative abundance = The mass spectrum of compoundT contains several fragments. The m/e values of two of these fragments are 29 and 91. Draw the structures of the ions responsible for these peaks. m/e structure of ion  The proton (1H) NMR spectrum of compoundT shows hydrogen atoms in different environments. Six of these environments are shown on the structure using letters a, b, c, d, e and f. N H a b c e d f Use the letters a, b, c, d, e and f to answer the questions that follow. The questions relate to the proton (1H) NMR spectrum of T. Proton d does not cause splitting of the peaks for protons c or e under the conditions used. Each answer may be one, or more than one, of the letters a, b, c, d, e and f. Identify the proton or protons with a chemical shift (δ) in the range 6.0 to 9.0.  Identify the proton or protons whose peak will disappear if D2O is added.  Identify the proton or protons whose peak is a triplet.  Identify the proton or protons with the lowest chemical shift (δ).  
22. Analytical techniques  →  22.2. Mass spectrometry
14. Hydrocarbons  →  14.2. Alkenes
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10
Valine (Val) and lysine (Lys) are amino acids. The structures of these amino acids can be found in the DataBooklet. The isoelectric point of an amino acid is the pH at which it exists as a zwitterion. The isoelectric point of valine is 6.0. The isoelectric point of lysine is 9.7. Draw the structure of valine at pH 6.0.  A solution of lysine is produced with pH 9.7. Dilute sulfuric acid is added slowly until the pH of the solution is 1.0. The sulfuric acid reacts with lysine to produce different organic ions that are not present in significant concentrations at pH 9.7. Draw the structures of three of the organic ions that form during the addition of sulfuric acid in the boxes. Draw the organic ion present at pH 1.0 in box C. A B C (pH 1.0)  Draw the structure of the dipeptide Val-Lys. The peptide bond should be shown fully displayed.  
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
11. Group 17  →  11.3. Some reactions of the halide ions
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