9701_w18_qp_43
A paper of Chemistry, 9701
Questions:
8
Year:
2018
Paper:
4
Variant:
3
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1
An aldehyde, an alkane and a carboxylic acid, all of similar volatility, are mixed together. The mixture is then analysed in a gas chromatograph. The gas chromatogram produced is shown. absorption time / mins Z X Y The separation of the compounds depends on their relative solubilities in the stationary phase. The stationary phase is a liquid alcohol. Complete the table to suggest which compound in the mixture is responsible for each peak X, Y and Z. Explain your answer by reference to the intermolecular forces of the compounds. peak organic compound explanation X Y Z  A student calculates the areas underneath the three peaks in the chromatogram. peak X Y Z 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 peakZ.  % of mixture responsible for peak Z = The mass spectrum of a halogenoalkane containing one chlorine atom or bromine atom will show an additional peak at M+2. State the isotopes of chlorine and bromine responsible for M+2 peaks. chlorine bromine  The mass spectrum of bromochloromethane, CH2BrCl, has a molecular ion peak, M, at an m / e value of 128. It also has M+2 and M+4 peaks. Suggest the identity of the molecular ions that give rise to these peaks. M peak M+2 peak M+4 peak  Halogenoalkanes can be formed from the reaction of an alkene with a hydrogen halide. Methylpropene reacts with hydrogen bromide to form 2-bromo-2-methylpropane. H2C CH3 CH3 C + HBr methylpropene 2-bromo-2-methylpropane H3C CH3 Br CH3 C Draw the mechanism of this reaction. Include all relevant curly arrows, dipoles and charges.  1-bromo-2-methylpropane is also formed in this reaction. Explain why 2-bromo-2-methylpropane will be the major product in this reaction. Explain what is meant by the term partition coefficient, Kpartition. The partition coefficient of organic compound H between dichloromethane and water is 4.75. ● 2.50 g of compoundH was dissolved in water and made up to 100 cm3 in a volumetric flask. ● 50 cm3 of this aqueous solution were shaken with 10 cm3 of dichloromethane. Calculate the mass of compoundH that was extracted into the dichloromethane.  mass of compound H extracted = g 
22. Analytical techniques  →  22.2. Mass spectrometry
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Ethanedioate ions, C2O4 2–, are bidentate ligands. Explain what is meant by the term ligand. Cr3+and C2O4 2–ions form the complex ion [Cr(C2O4)2(H2O)2]–. Draw two stereoisomers of this complex ion. You may use O O to represent C2O4 2–. Cr Cr  The solubility of calcium ethanedioate, CaC2O4, is 6.65×10–3 g dm–3 at 298 K. Write an expression for the solubility product, Ksp, of CaC2O4. Include its units. Ksp =  units =  Calculate the numerical value of Ksp CaC2O4 at 298 K. Give your answer in standard form to two significant figures.  Ksp CaC2O4 = 
2. Atoms, molecules and stoichiometry  →  2.3. Formulas
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Complete the table to show the total number of unpaired electrons in the 3d and 4s orbitals of each isolated gaseous atom. number of unpaired electrons 3d 4s Cr Mn Fe  Solid potassium manganate(, KMnO4, decomposes on heating to form manganese(oxide, potassiummanganate(and a colourless gas. Construct an equation for this reaction. Explain the origin of colour in transition element complexes. The reaction scheme shows some reactions of [Cu(H2O)6]2+. [Cu(H2O)6]2+ precipitate A solution of B CuCO3NaOHreaction 3 reaction 2 reaction 1 excess NH3solution of C reaction 4 CH3CO2HWrite the formulae of precipitate A, complex ion B, compound C  Identify a suitable reagent for reaction3. Write an equation for reaction4. Describe two visual observations that would be made during reaction 4. Platin, Pt(NH3)2Cl 2, is a neutral complex of platinum(. Explain why Pt(NH3)2Cl 2 has no charge. Pt(NH3)2Cl 2, displays cis-trans isomerism. Draw the structure of trans-platin. State its shape and the Cl –Pt–Cl bond angle. shape Cl –Pt–Cl bond angle  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 nedaplatin has been developed. Nedaplatin can be synthesised from cis‑platin, Pt(NH3)2Cl 2, by replacing the two chloride ion ligands with a single bidentate ligand as shown. Suggest the structure for nedaplatin. O– –O O Pt(NH3)2Cl 2 cis-platin + nedaplatin  
3. Chemical bonding  →  3.4. Covalent bonding and coordinate (dative covalent) bonding
14. Hydrocarbons  →  14.2. Alkenes
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The enthalpy change of solution, , of the Group2 sulfates becomes more endothermic down the group. State and explain the trend in the solubility of the Group 2 sulfates down the group. Write the expression for Kw , the ionic product of water. Kw =  The numerical value of Kw increases with increasing temperature. Place a tick () in the appropriate column in each row to show the effect of increasing the temperature of water on the pH and on the ratio [H+] : [OH–]. effect of increasing temperature of water decrease stay the same increase pH ratio [H+] : [OH–]  An aqueous solution of sodium hydroxide has a pH of 13.25 at 298 K. Calculate the concentration of this sodium hydroxide solution.  concentration = mol dm–3 Buffer solutions are used to regulate the pH of a solution to keep its pH value within a narrow range. Write two equations to describe how hydrogencarbonate ions, HCO3 –, and carbonic acid, H2CO3, control the pH of blood. The Ka for ethanoic acid is 1.75×10–5 mol dm–3 at 298 K. When ethanoic acid is dissolved in water, an equilibrium mixture containing two acid‑base pairs is formed. Write an equation for this equilibrium. In the boxes label each species acidic or basic to show its behaviour in this equilibrium. CH3CO2H + +  A buffer solution was prepared by adding 30.0 cm3 of 0.25 mol dm–3 ethanoic acid, an excess, to 20.0 cm3 of 0.15 mol dm–3 sodiumhydroxide. Calculate the pH of the buffer solution formed at 298 K. Give your answer to one decimal place.  pH = Titration curves for two different acid-base reactions, M and N, are shown. pH volume of acid added / cm3 pH volume of acid added / cm3 reaction M reaction N Use the titration curve for reaction M to deduce the volume of acid added at the end‑point for this titration.  volume of acid added at the end-point = cm3 The table shows some acid-base indicators. name of indicator pH range of colour change malachite green 0.2–1.8 bromocresol green 3.8–5.4 bromothymol blue 6.0–7.6 thymolphthalein 9.3–10.6 Name a suitable indicator for each of the acid-base titrations M and N. Explain your answers. reaction M reaction N explanation  
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
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Polyhydroxyamide is a fire-resistant polyamide which is formed from the two monomers, F and G. HO2C CO2H F H2N NH2 OH G Predict the number of peaks that will be seen in the carbon-13 NMR spectra of F and G. number of peaks F G  Draw the repeat unit of polyhydroxyamide. The amide bond should be shown displayed.  When polyis formed from ethene, many bonds are broken and formed. Place one tick () in each row of the table to indicate the types of bonds broken and formed in this process. σ-bonds only π-bonds only both σ- and π-bonds bonds broken bonds formed  Addition polymers can be classified into two types. ● ● homopolymer - a polymer made up of the same monomer unit ● ● copolymer - a polymer made up of two or more different monomer units The reaction of propene, CH3CH=CH2, with phenylethene, C6H5CH=CH2, gives a copolymer. Draw a length of the chain of this copolymer that contains one molecule of each monomer.  Polyalkenes biodegrade very slowly. Explain why by referring to the structures of the polymers. Some polymers will degrade in the environment. Describe two processes by which this occurs.  
20. Polymerisation  →  20.1. Addition polymerisation
14. Hydrocarbons  →  14.2. Alkenes
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Use the Data Booklet to draw the structure of the dipeptide val-lys. The peptide bond should be shown displayed.  The isoelectric point is the pH at which an amino acid exists as a zwitterion. The isoelectric point of valine is 6.0 and of lysine is 9.8. A mixture of the dipeptide, val-lys, and its two constituent amino acids, valine and lysine, was analysed by electrophoresis using a buffer at pH 6.0. Draw and label three spots on the diagram of the electrophoresis paper to indicate the likely position of each of these three species after electrophoresis. Explain your answer. + – mixture applied here explanation  
7. Equilibria  →  7.2. Brønsted–Lowry theory of acids and bases
14. Hydrocarbons  →  14.2. Alkenes
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Chlorobenzene and phenol both show a lack of reactivity towards reactants that cause the breaking of the C–X bond (X = Cl or OH). Explain why. When phenol is reacted with bromine dissolved in an inert solvent, two isomeric bromophenols, C6H4BrOH, are formed. Suggest structures for these products. Name each compound. name: name:  A student suggested that phenol can be prepared from benzene by the method shown. NO2 NH2 OH phenol step 1 step 2 step 4 step 3 NaNO2/ HCl 5 °C K Suggest reagents and conditions for each of the following steps. step 1 step 2 step 4  Deduce the structure for K and draw its structural formula in the box. Name the mechanism for step1. Write an equation for step2. Use [H] for the reducing agent in this equation.  
15. Halogen compounds  →  15.1. Halogenoalkanes
21. Organic synthesis  →  21.1. Organic synthesis
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Entropy is a measure of the disorder of a system. Assume the entropy, S, for H2O is zero at 0 K. Sketch a graph on the axes to show how the entropy changes for H2O between 0 K and 300 K. S / J K–1 mol–1 temperature / K  Place one tick () in each row of the table to show the sign of the entropy changes, ΔS. ΔS is negative ΔS is positive solid dissolving in water water boiling to steam  The equation for a reaction that produces methanol is shown. CO2+ 3H2CH3OH+ H2OUse relevant bond energies from the Data Booklet to calculate the enthalpy change, ΔH, for this gas phase reaction. ΔH = kJ mol–1 At 298 K, both products of this reaction are liquid. CO2+ 3H2CH3OH+ H2OΔH o = –131 kJ mol–1 Standard entropies are shown in the table. substance CO2H2CH3OHH2OS o / J K–1 mol–1 +214 +131 +127 +70 Calculate the standard entropy change, ΔS o, for this reaction. ΔS o = J K–1 mol–1 Calculate the standard Gibbs free energy change, ΔG o, for this reaction at 298 K. ΔG o = kJ mol–1 Predict the effect of increasing the temperature on the feasibility of this reaction. In a methanol-oxygen fuel cell, CH3OHand O2are in contact with two inert electrodes immersed in an acidic solution. The half-equation for the reaction at the methanol electrode is shown. CH3OH + H2O CO2 + 6H+ + 6e– E o = – 0.02 V Use the Data Booklet to write an equation for the overall cell reaction. Use E o values to calculate the for this reaction.  = V 
5. Chemical energetics  →  5.1. Enthalpy change, \(\Delta H\)
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