9701_w18_qp_42
A paper of Chemistry, 9701
Questions:
9
Year:
2018
Paper:
4
Variant:
2
Login to start this paper & get access to powerful tools
1
An alkene, a carboxylic acid and a ketone, all of similar volatility, are mixed together. The mixture is then analysed by gas chromatography. The gas chromatogram produced is shown. absorption time / mins J K L The separation of the three compounds depends on their relative solubilities in the liquid stationary phase. The liquid stationary phase is an alkane. Complete the table to suggest which compound in the mixture is responsible for each peak J, K and L. Explain your answer by reference to the intermolecular forces of each compound. peak organic compound explanation J K L  A student calculates the areas underneath the three peaks in the chromatogram. peak J K L area / mm2 The area underneath each peak is proportional to the mass of the respective compound. Calculate the percentage by mass in the original mixture of the compound responsible for peak K.  % of mixture responsible for peak K = Chlorobenzene can be prepared from benzene as shown. Cl 2 Cl Al Cl 3 Aluminium chloride, Al Cl 3, catalyses this reaction. Write an equation to show how Al Cl 3 generates the electrophile needed in this reaction. Draw the mechanism of the reaction between this electrophile and benzene to form chlorobenzene. Include all relevant curly arrows and charges.  Write an equation to show how the catalyst is regenerated. Catalysts can be heterogeneous or homogeneous. Explain what is meant by a homogeneous catalyst. Complete the table by placing one tick () in each row to indicate the mode of action of the catalyst in each reaction. heterogeneous homogeneous Rh in the removal of NO2 from exhaust gases of cars Fe3+ in the I – / S2O8 2– reaction  
14. Hydrocarbons  →  14.1. Alkanes
8. Reaction kinetics  →  8.3. Homogeneous and heterogeneous catalysts
Open
2
Complete the electronic configuration for Cu and Cu2+. 3d [Ar] Cu [Ar] Cu2+ 4s  The 3d orbitals in an isolated Cu2+ ion are degenerate. Explain what is meant by the term degenerate in this context. Complete the diagram to describe the splitting of the 3d orbital energy levels in an octahedral complex. energy isolated Cu2+ ion Cu2+ in octahedral complex  1,2-diaminoethane, H2NCH2CH2NH2, en, is a bidentate ligand. Explain what is meant by the term bidentate. Cu2+ ions and en form the complex ion [Cu3]2+. Draw the two optical isomers of this complex ion. You may use N N to represent en. Cu Cu  
1. Atomic structure  →  1.3. Electrons, energy levels and atomic orbitals
Open
3
The reaction scheme shows some reactions of [Co(H2O)6]2+. [Co(H2O)6]2+ CO3 2–[Co(H2O)4(OH)2] solution of A precipitate B reaction 1 reaction 3 reaction 2 excess NH3Write the formulae of the following species. A B  State a suitable reagent for reaction1. Write an equation for reaction2. Write an ionic equation for reaction3. Co2+ ions catalyse the oxidation of 2,3-dihydroxybutanedioate ions, C4H4O6 2–, to methanoate ions, HCO2 –, carbon dioxide and water. What property of transition elements allows Co2+ ions to act as a catalyst? Draw the structure of the 2,3-dihydroxybutanedioate ion.  Complete the equation for the oxidation of 2,3-dihydroxybutanedioate. Use [O] for the oxidising agent in this reaction. C4H4O6 2– + ���������������������������������������������������������������������������������� Platin, Pt(NH3)2Cl 2, displays cis-trans isomerism. Draw the structures of these isomers. cis isomer trans isomer  Cis-platin is an effective anti-cancer drug. Describe the action of cis-platin in this role. The use of cis‑platin can cause side effects so carboplatin has been developed. Carboplatin can be synthesised from cis‑platin, Pt(NH3)2Cl 2, by replacing the two chloride ion ligands with a single cyclobutane‑1,1‑dicarboxylate ion ligand as shown. Pt(NH3)2Cl 2 + cis-platin O O O– O– [C6H6O4]2– + 2Cl – cyclobutane-1,1-dicarboxylate ion carboplatin Suggest the structure for carboplatin and draw it in the box. 
17. Carbonyl compounds  →  17.1. Aldehydes and ketones
14. Hydrocarbons  →  14.2. Alkenes
18. Carboxylic acids and derivatives  →  18.1. Carboxylic acids
Open
4
Calcium nitride, Ca3N2 , reacts readily with water to form a white precipitate suspended in an alkaline solution. The oxidation number of nitrogen does not change during the reaction. Construct an equation for the reaction of Ca3N2 with water. The enthalpy changes of solution, , of the hydroxides of the Group2 elements become less endothermic down the group. State and explain the trend in the solubilities of the Group2 hydroxides. Complete the energy cycle to show the enthalpy changes that occur in the transformations between aqueous ions, gaseous ions and an ionic solid. On your diagram label each enthalpy change with its appropriate symbol; lattice energy, , enthalpy change of hydration, , or enthalpy change of solution, . Complete the three arrows showing the correct direction of each enthalpy change. aqueous ions gaseous ions ionic solid  The numerical value of the solubility product, Ksp, of CaF2 is 3.45×10–11 at 298 K. Write an expression for the solubility product of CaF2. Include its units. Ksp =  units =  Calculate the solubility of CaF2 at 298 K.  solubility = mol dm–3 
5. Chemical energetics  →  5.1. Enthalpy change, \(\Delta H\)
11. Group 17  →  11.4. The reactions of chlorine
Open
5
Explain why the thermal stability of the Group2 nitrates increases down the group. Sodiumnitrite, NaNO2, is a decomposition product from heating sodiumnitrate, NaNO3. A student analysed a sample of sodium nitrite by titration with aqueous cerium(ions, Ce4+. The equation for the titration reaction is shown. NO2 –+ 2Ce4++ H2O2Ce3++ NO3 –+ 2H+● ●0.138 g of impure sodium nitrite was dissolved in water and made up to 100 cm3 in a volumetric flask. ● ●25.0 cm3 of this solution required 21.80 cm3 of 0.0400 mol dm–3 Ce4+to reach the end‑point. You should assume the impurity does not react with Ce4+. Calculate the percentage purity of the sample of sodium nitrite.  % Acidified manganate(ions, MnO4 –, can also be used to analyse solutions containing nitrite ions, NO2 –, by titration. In acidic solution, NO2 – ions exist as HNO2. Use the DataBooklet to construct an ionic equation for this reaction. Use E o values to calculate the for this reaction.  = V Nitrousacid, HNO2, is a weak acid with a Ka of 6.9×10–4 mol dm–3 at 298 K. Explain the difference between a strong acid and a weak acid. Write the expression for the acid dissociation constant, Ka, for HNO2. Ka =  Calculate the pH of 0.15 mol dm–3 HNO2.  pH = Calculate the percentage of HNO2 molecules that are ionised in 0.15 mol dm–3 HNO2.  % ionisation = Solutions containing a mixture of HNO2 and NaNO2 are buffer solutions. Define what is meant by the term buffer solution. Write two equations to show how a solution containing a mixture of HNO2 and NaNO2 acts as a buffer. Nitrousacid is used in the preparation of diazonium salts. The –N2 + group in the diazonium ion can be replaced with Cl, Br or CN as shown. The reagent used is a copper(salt, CuX. N2 + X CuX diazonium ion where X = Cl, Br or CN This reaction can be used in the synthesis of compound Z as shown. N2 + H3C H3C CN W Y H3C H3C reaction 1 aq HCl, heat reaction 2 an excess of MnO4 – / H+ heat reaction 3 Z Suggest the reagent used in reaction 1. Suggest structures of compounds Y and Z and draw them in the boxes above. Compounds W and Z were analysed using carbon‑13 NMR spectroscopy. Predict the number of peaks in the carbon‑13 NMR spectra of W and Z. number of peaks W Z  
12. Nitrogen and sulfur  →  12.1. Nitrogen and sulfur
10. Group 2  →  10.1. Similarities and trends in the properties of the Group 2 metals, magnesium to barium, and their compounds
Open
6
2-hydroxypropanoic acid can be synthesised in four steps from ethanoicacid. OH O ethanoic acid step 1 Cl O CN O O OH O OH OH O 2-hydroxypropanoic acid step 2 step 3 step 4 Suggest a reagent for step 2. Suggest reagents and conditions for steps 1 and 4. step 1 step 4  Compound R can be used in the synthesis of compound T as shown. step I warm step II LiAl H4 Cl NH2 O R S C5H9NO T Suggest the structures of S and T and draw them in the boxes. Name the type of reaction for stepI and stepII. step I step II  Compound R can be polymerised. Draw a section of this polymer showing two repeat units.  
21. Organic synthesis  →  21.1. Organic synthesis
18. Carboxylic acids and derivatives  →  18.1. Carboxylic acids
Open
7
Polyurethanes are polymers made by the reaction of a diisocyanate with a diol as shown. R1 and R2 are hydrocarbon groups. C O N H N H R1 R2 O O C C N N R1 R2 OH HO a diol C O O O + a diisocyanate a polyurethane Lycra® is a polyurethane formed from the diisocyanateP and HOCH2CH2OH. N CH2 P N C O C O Give the molecular formula for P. Draw the repeat unit of Lycra®.  Fibres of Lycra® are strong due to the intermolecular forces between the polymer chains. Complete the table to identify two intermolecular forces responsible for this property and the groupinvolved. intermolecular force groupinvolved  Name one example of each of the following types of polymer. type of polymer example synthetic polyamide synthetic polyester conducting polymer non-solvent based adhesive  
20. Polymerisation  →  20.1. Addition polymerisation
Open
8
Chloramine, NH2Cl, can be used in the treatment of drinking water to kill bacteria. Excess chloramine in water is destroyed using UV light. The mechanism for this involves free radicals. The initiation step in this process is shown. UV NH2Cl ●NH2 + ●Cl What is meant by the term free radical ? The equation for a possible propagation step in the process is shown. NH2Cl + ●Cl ●NHCl + HCl Suggest an equation for a possible termination step in this process. Draw the ‘dot-and-cross’ diagram of NH2Cl. Show outer electrons only.  State the hybridisation of the nitrogen atom and suggest the H–N–Cl bond angle in the NH2Cl molecule. hybridisation of N H–N–Cl bond angle  Some values for standard enthalpy changes of formation, , and standard entropies, S o, are given in the table. / kJ mol–1 S o / J K–1 mol–1 NH2Cl +80.1 +241 NH3– 45.9 +198 N2H4+95.4 +237 HCl –92.3 +187 Define the meaning of the term entropy. Hydrazine, N2H4, can be produced from chloramine and ammonia as shown. NH2Cl + NH3N2H4+ HCl Calculate the standard entropy change, ΔS o, for this reaction. ΔS o = J K–1 mol–1 Calculate the standard enthalpy change, ΔH o, for this reaction.  ΔH o = kJ mol–1 Calculate the standard Gibbs free energy change, ΔG o, for this reaction at 298 K. ΔG o = kJ mol–1 Explain, with reference to ΔG o, why this reaction becomes less feasible at higher temperatures. Compare and explain the basicities of ammonia, ethylamine and phenylamine. 
11. Group 17  →  11.4. The reactions of chlorine
14. Hydrocarbons  →  14.1. Alkanes
Open
9
Use information from the Data Booklet to draw the structure of the dipeptide glu‑cys.  The isoelectric point is the pH at which an amino acid exists as a zwitterion. The isoelectric point of glutamicacid is 3.2 and of cysteine is 5.0. A mixture of the dipeptide glu-cys and its two constituent amino acids, glutamicacid and cysteine, was analysed by electrophoresis using a buffer at pH5.2. The results obtained are shown. + – E F G mixture applied here Suggest identities for the species responsible for spots E, F and G. Explain your answers. spot identity E F G explanation  
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
Open