Chemistry 0620/41 October/November 2019: question paper and mark scheme

Question

This question is about ions and ionic compounds. (a) Choose from the following list of ions to answer the questions. Br – Ca2+ Cl – Cr3+ Cu2+ K+ Li+ Na+ SO32– SO42– Each ion may be used once, more than once or not at all. State which ion: (i) gives a lilac colour in a flame test . …… [1] (ii) forms a grey-green precipitate with aqueous ammonia . …… [1] (iii) forms a white precipitate with aqueous sodium hydroxide …… [1] (iv) forms a cream precipitate with acidified aqueous silver nitrate …… [1] (v) forms a white precipitate with acidified aqueous barium nitrate. …… [1] (b) Describe how to do a flame test on a sample of a salt. . …… . …… . …… . …… [2] (c) Magnesium phosphate contains magnesium ions, Mg2+, and phosphate ions, PO43–. Deduce the formula of magnesium phosphate. . …… [1] [Total: 8]

Question

(a) Sulfur exists as a number of different isotopes. What is meant by the term isotopes? . …… . …… . …… [2] (b) A sulfide ion has the symbol shown. 34 16 S2– (i) How many neutrons are contained in this sulfide ion? . …… [1] (ii) How is a sulfide ion, S2–, formed from a sulfur atom? . …… [1] (iii) Which element forms an ion with a 2+ charge that has the same number of electrons as a S2– ion? . …… [1] (c) The manufacture of sulfuric acid by the Contact process occurs in four stages. stage 1 Molten sulfur is burned in air to produce sulfur dioxide gas. stage 2 Sulfur dioxide is reacted with oxygen to form sulfur trioxide. stage 3 Sulfur trioxide is combined with concentrated sulfuric acid to form oleum, H2S2O7. stage 4 Oleum is added to water to form sulfuric acid. (i) Complete the chemical equation for stage 1 by adding the appropriate state symbols. S(……) + O2(……) SO2(……)[1] (ii) Name the catalyst used in stage 2 and state the temperature used. catalyst …… temperature …… °C [2] (iii) Write chemical equations for the reactions in stage 3 and stage 4. stage 3 …… stage 4 …… [2] (d) Sulfur dioxide is a toxic gas. (i) State one environmental reason why sulfur dioxide should not be released into the atmosphere. . …… [1] (ii) Describe the test for sulfur dioxide. test . …… . …… observations …… . …… [2] (e) Sulfur dioxide reacts with aqueous sodium sulfite to produce a compound with the following composition by mass: 29.1% Na, 40.5% S and 30.4% O. Calculate the empirical formula of this compound. empirical formula = …… [3] [Total: 16]

Question

This question is about metals and metal oxides. (a) Most metals have a high melting point. State one other physical property that all metals have. . …… [1] (b) Iron often rusts. Name the two substances, other than iron, that must be present for iron to rust. 1 . …… 2 . …… [1] (c) Iron can be obtained by heating iron(III) oxide with zinc powder. Fe2O3 + 3Zn 2Fe + 3ZnO (i) What can be deduced about the reactivity of zinc from this reaction? . …… [1] (ii) The ionic equation for this reaction is shown. 2Fe3+ + 3Zn 2Fe + 3Zn2+ Identify the oxidising agent in this reaction. Explain your answer in terms of electron transfer. oxidising agent . …… explanation …… . …… [2] (d) Zinc oxide is amphoteric. Describe two simple experiments to show that zinc oxide is amphoteric. Name the reagents you would use and describe the observations you would make. reagent 1 …… observation …… reagent 2 …… observation …… [3] [Total: 8]

Question

Insoluble salts can be made by precipitation reactions. A student mixed solutions of some soluble salts. The results the student obtained are shown in the table. second salt solution Co(NO3)2(aq) AgNO3(aq) Pb(NO3)2(aq) NaI(aq) no change yellow precipitate yellow precipitate first salt Na2CO3(aq) purple precipitate yellow precipitate white precipitate solution Na2SO4(aq) no change white precipitate white precipitate All sodium salts are soluble in water. Use only results from the table to answer the following questions. (a) Name: (i) an insoluble cobalt salt …… [1] (ii) an insoluble yellow lead salt. …… [1] (b) Write the chemical equation for the reaction in which silver carbonate is formed. . …… [2] (c) Write the ionic equation for the reaction in which lead(II) iodide is formed. . …… [2] (d) Aqueous silver nitrate produces a yellow precipitate with both iodide ions and carbonate ions. When testing an unknown solution for iodide ions, the aqueous silver nitrate is acidified. Explain why the aqueous silver nitrate is acidified. . …… . …… [1] [Total: 7]

Question

(a) Part of the structure of synthetic polymer A is shown. CH3 CH3 CH3 CH3 CH3 CH3 C C C C C C CH3 CH3 CH3 CH3 CH3 CH3 (i) What type of synthetic polymer is A? . …… [1] (ii) Deduce the empirical formula of polymer A. . …… [1] (iii) Draw the structure of the monomer from which polymer A is made. [2] (b) The formula C4H10 represents two different structural isomers. (i) What is meant by the term structural isomers? . …… . …… . …… [2] (ii) Draw the structures of two structural isomers with the formula C4H10. Show all of the atoms and all of the bonds. [2] (iii) All structural isomers of C4H10 are flammable. Write a chemical equation for the incomplete combustion of C4H10. . …… [2] [Total: 10]

Question

Dilute hydrochloric acid, HCl (aq), reacts with aqueous sodium carbonate, Na2CO3(aq). The chemical equation for the reaction is shown. 2HCl + Na2CO3 2NaCl + CO2 + H2O (a) A 25.0 cm3 portion of Na2CO3(aq) was placed in a conical flask with a few drops of a suitable indicator. It was titrated against HCl (aq) of concentration 0.180 mol /dm3. 20.0 cm3 of HCl (aq) was required to reach the end-point. Calculate the concentration of the Na2CO3(aq), in mol / dm3, using the following steps. ●● Calculate the number of moles of HCl used in the titration. …… mol ●● Calculate the number of moles of Na2CO3 contained in the 25.0 cm3 portion of Na2CO3(aq). …… mol ●● Calculate the concentration of the Na2CO3(aq) in mol / dm3. …… mol / dm3 [3] (b) In another experiment, the volume of carbon dioxide, CO2, produced was 48.0 cm3, measured at room temperature and pressure. How many moles of CO2 is this? moles of CO2 = …… mol [1] (c) A sample of concentrated hydrobromic acid, HBr(aq), was electrolysed using platinum electrodes. The concentration of the hydrobromic acid was 8.89 mol / dm3. (i) Calculate the concentration of the HBr(aq) in g / dm3. concentration of HBr(aq) = …… g / dm3 [1] (ii) Explain why concentrated HBr(aq) can conduct electricity. . …… . …… . …… [2] (iii) Magnesium is not a suitable material from which to make the electrodes. Explain why. . …… . …… [1] (iv) Predict the product formed at the anode when concentrated HBr(aq) is electrolysed. . …… [1] (v) Write the ionic half-equation for the reaction occurring at the cathode. . …… [2] [Total: 11]

Question

This question is about ethanol. (a) Ethanol that is suitable for use as a fuel can be manufactured from sugars such as glucose, C6H12O6, by a two-step process. Describe how this can be done. In your answer, include: ●● an equation for the reaction in which ethanol is formed ●● the essential conditions for the reaction in which ethanol is formed ●● the name of the process used to obtain ethanol that is pure enough to use as a fuel from the reaction mixture. . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… [5] (b) The equation for the complete combustion of ethanol is shown. H H H C C O H + 3 O O 2 O C O + 3 H O H H H Use the bond energies in the table to calculate the energy change, in kJ / mol, for the complete combustion of ethanol. bond energy bond in kJ / mol C–C 347 C–H 413 C–O 358 C=O 805 O–H 464 O=O 498 ●● Energy needed to break bonds. …… kJ ●● Energy released when bonds are formed. …… kJ ●● Energy change for the complete combustion of ethanol. energy change = …… kJ / mol [3] (c) Ethanol can be oxidised by hydrogen peroxide to form ethanal, CH3CHO. A catalyst for this reaction is Fe3+. (i) What is meant by the term catalyst ? . …… . …… . …… [2] (ii) The structure of ethanal is shown. H H C C O H H Complete the dot-and-cross diagram to show the electron arrangement in a molecule of ethanal. Show outer shell electrons only. H H C C O H H [3] (iii) The table gives the boiling points of ethanal and ethanol. substance boiling point / °C ethanal 20 ethanol 78 In terms of attractive forces between particles, suggest why ethanal has a lower boiling point than ethanol. . …… . …… [1] (d) Ethene gas reacts with steam to form gaseous ethanol. C2H4(g) + H2O(g) CH3CH2OH(g) The reaction can reach a position of equilibrium. The forward reaction is exothermic. (i) State and explain the effect of increasing the pressure on the position of equilibrium. All other conditions are unchanged. . …… . …… . …… [2] (ii) Increasing the pressure of a gas increases its concentration. State and explain the effect of increasing the pressure on the rate of the reaction. All other conditions are unchanged. . …… . …… . …… [2] (iii) State and explain the effect of increasing the temperature on the position of equilibrium. All other conditions are unchanged. . …… . …… . …… [2] [Total: 20] The Periodic Table of Elements Group I II III IV V VI VII VIII 1 2 H He hydrogen helium Key 1 4 3 4 atomic number 5 6 7 8 9 10 Li Be atomic symbol B C N O F Ne lithium beryllium name boron carbon nitrogen oxygen fluorine neon 7 9 relative atomic mass 11 12 14 16 19 20 11 12 13 14 15 16 17 18 Na Mg Al Si P S Cl Ar sodium magnesium aluminium silicon phosphorus sulfur chlorine argon 23 24 27 28 31 32 35.5 40 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton 39 40 45 48 51 52 55 56 59 59 64 65 70 73 75 79 80 84 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon 16 85 88 89 91 93 96 – 101 103 106 108 112 115 119 122 128 127 131 55 56 57–71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 lanthanoids Cs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn caesium barium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury thallium lead bismuth polonium astatine radon 133 137 178 181 184 186 190 192 195 197 201 204 207 209 – – – 87 88 89–103 104 105 106 107 108 109 110 111 112 114 116 actinoids Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Cn Fl Lv francium radium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium flerovium livermorium – – – – – – – – – – – – – 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 lanthanoids La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium 139 140 141 144 – 150 152 157 159 163 165 167 169 173 175 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 actinoids Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr actinium thorium protactinium uranium neptunium plutonium americium curium berkelium californium einsteinium fermium mendelevium nobelium lawrencium – 232 231 238 – – – – – – – – – – – The volume of one mole of any gas is 24 dm3 at room temperature and pressure (r.t.p.).