Chemistry 0620/42 February/March 2022: question paper and mark scheme

Question

This question is about the first 30 elements in the Periodic Table. Name the element which: (e) is the gas with the slowest rate of diffusion at room temperature (f) has an anhydrous chloride which turns pink when water is added (g) has aqueous ions which form a white precipitate when added to aqueous silver ions …… [1] (h) forms a blue hydroxide which dissolves in aqueous ammonia (i) is added to molten iron to remove impurities in the steel making process [Total: 10]

Question

A student adds excess large pieces of magnesium carbonate, MgCO3, to dilute hydrochloric acid, HCl, and measures the volume of carbon dioxide gas, CO2, given off. (a) Add the missing state symbols to the chemical equation for the reaction. MgCO3 …… + 2HCl …… → MgCl 2(aq) + H2O …… + CO2 …… [1] (b) Complete the dot-and-cross diagram to show the electron arrangement of the ions in magnesium chloride. The inner shells have been drawn. Give the charges on the ions. Mg Cl Cl [3] (c) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of carbon dioxide. Show outer shell electrons only. O C O [2] (d) The graph shows how the volume of carbon dioxide gas changes with time. volume of carbon dioxide gas 0 0 time (i) Describe how the graph shows that the rate of this reaction decreases as time increases. . …… . …… [1] (ii) Explain, in terms of particles, why the rate of this reaction decreases as time increases. . …… . …… [2] (iii) The student repeats the experiment using powdered MgCO3 instead of large pieces. All other conditions stay the same. On the grid, draw the line expected when powdered MgCO3 is used instead of large pieces. [2] (e) Determine the volume of CO2 gas given off when excess MgCO3 is added to 25.0 cm3 of 0.400 mol / dm3 HCl at room temperature and pressure. MgCO3 + 2HCl → MgCl 2 + H2O + CO2 Use the following steps. ● Calculate the number of moles of HCl in 25.0 cm3 of 0.400 mol / dm3 of acid. …… mol ● Determine the number of moles of CO2 gas given off. …… mol ● Calculate the volume of CO2 gas given off in cm3. …… cm3 [3] [Total: 14]

Question

Nitrogen dioxide, NO2, is an atmospheric pollutant and is formed in car engines. (a) Explain how nitrogen dioxide is formed in car engines. …… [2] (b) Nitrogen dioxide causes respiratory problems. State one other adverse effect of nitrogen dioxide. …… [1] (c) Nitrogen dioxide emissions can be reduced by adding an aqueous solution of urea, (NH2)2CO, to car exhaust gases. The heat of the exhaust gases breaks down the urea into simpler substances. (i) Name the type of reaction which occurs when a substance is heated and breaks down into simpler substances. . …… [1] (ii) One molecule of urea breaks down to form one molecule of ammonia and one other molecule. Complete the chemical equation to show the formula of the other molecule formed in this reaction. (NH2)2CO → NH3 + …… [1] (iii) State the test for ammonia. test . …… observations …… [2] (d) The ammonia formed reacts with nitrogen dioxide to form nitrogen and water. (i) Balance the equation for this reaction. ……NO2 + ……NH3 → ……N2 + 12H2O [2] (ii) State how the equation shows that the nitrogen in nitrogen dioxide is reduced. . …… [1] (iii) This reaction is a redox reaction. State the meaning of the term redox. . …… [1] (e) 135 moles of urea, (NH2)2CO, is stored in the tank of a car. Calculate the mass, in kg, of the stored (NH2)2CO. mass of (NH2)2CO = …… kg [2] (f) Another oxide of nitrogen formed in car engines is nitrogen monoxide, NO. A catalytic converter removes NO by reacting it with a gas formed by incomplete combustion of the fuel. Two non‑toxic gases are formed. (i) Name the gas formed by incomplete combustion of the fuel. . …… [1] (ii) Name the two non‑toxic gases formed. [Total: 15]

Question

This question is about chemical reactions and electricity. (a) The diagram shows the apparatus used in the production of electrical energy in a simple cell. voltmeter V zinc electrode iron electrode electrolyte The zinc electrode dissolves in the electrolyte forming Zn2+(aq) ions. (i) Draw an arrow on the diagram to show the direction of electron flow. [1] (ii) Write the ionic half-equation for the reaction that occurs when the zinc electrode dissolves. . …… [2] (b) The reading on the voltmeter can be increased if either zinc or iron is replaced by another metal. (i) Name a metal that can replace zinc and increase the reading on the voltmeter. . …… [1] (ii) Name a metal that can replace iron and increase the reading on the voltmeter. . …… [1] (c) Fuel cells are used to generate electricity. (i) Name the reactants in a fuel cell. . …… [1] (ii) Name the waste product of a fuel cell. . …… [1] (d) Electricity can be used to break down aqueous or molten ionic compounds. (i) Name the process which uses electricity to break down aqueous or molten ionic compounds. . …… [1] (ii) Explain why the ionic compound needs to be aqueous or molten. . …… [1] (e) Brine is concentrated aqueous sodium chloride. (i) Name three substances which are manufactured by passing electricity through brine. 1 . …… 2 . …… 3 . …… [3] (ii) Name a different substance formed when molten sodium chloride is used instead of concentrated aqueous sodium chloride. . …… [1] [Total: 13]

Question

This question is about alkanes and alkenes. (a) Short-chain alkanes and alkenes can be formed from long-chain alkanes in a chemical reaction. (i) Name the type of chemical reaction which forms short‑chain alkanes and alkenes from long‑chain alkanes. . …… [1] (ii) Decane has 10 carbon atoms. It forms ethane and ethene as the only products in this type of chemical reaction. Write the chemical equation for this reaction. . …… [3] (b) Ethane reacts with chlorine at room temperature to form chloroethane, C2H5Cl, and one other product. (i) Name the other product formed. . …… [1] (ii) State the condition needed for this reaction to take place. . …… [1] (c) Ethene reacts with chlorine at room temperature to form dichloroethane, C2H4Cl 2. C2H4 + Cl 2 → C2H4Cl 2 (i) State why this is an addition reaction. . …… [1] (ii) The chemical equation for this reaction can be represented as shown. H H H H C C + Cl Cl Cl C C Cl H H H H The energy change for the reaction is –180 kJ / mol. Use the bond energies in the table to calculate the bond energy of a C–Cl bond, in kJ / mol. bond C–H C=C Cl –Cl C–C bond energy in kJ / mol 410 610 240 350 Use the following steps. step 1 Calculate the energy needed to break bonds. energy needed to break bonds = …… kJ step 2 Use your answer in step 1 and the energy change for the reaction to determine the energy released when bonds are formed. energy released when bonds form = …… kJ step 3 Use your answer in step 2 and bond energy values to determine the energy of a C–Cl bond. bond energy of a C–Cl bond = …… kJ / mol [4] [Total: 11]

Question

The names of four esters are listed. methyl propanoate ethyl propanoate propyl propanoate butyl propanoate (a) Esters are a family of organic compounds with similar chemical properties. They can be represented by the formula CnH2nO2. (i) State the name given to a family of organic compounds with similar chemical properties. . …… [1] (ii) Explain why members of a family of organic compounds have similar chemical properties. . …… [1] (iii) State the name given to a formula such as CnH2nO2. . …… [1] (iv) Determine the value of ‘n’ in butyl propanoate. . …… [1] (b) All four of the esters in the list are liquids at room temperature. Name the technique used to separate ethyl propanoate from a mixture of the four esters. …… [2] (c) All four esters can be made by reacting different alcohols with the same substance. (i) Name this substance and draw its structure. Show all of the atoms and all of the bonds. name …… structure [2] (ii) Name the alcohol used to make methyl propanoate. . …… [1] (d) Other esters, not in the list, have the same molecular formula as propyl propanoate, but different structures. (i) State the term used to describe substances with the same molecular formula but different structures. . …… [1] (ii) Name two esters with the same molecular formula as propyl propanoate. 1 . …… 2 . …… [2] (e) Polyesters can be made from the two different molecules shown. O O H O C C O H and H O O H (i) Complete the diagram to show a section of the polyester made from these two molecules. Include all of the atoms and all of the bonds in the linkages. [3] (ii) Name the type of polymerisation that takes place when this polymer forms. . …… [1] (iii) Name a polyester. . …… [1] [Total: 17] 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.).