Chemistry 0620/41 May/June 2021: question paper and mark scheme

Question

Give the name of the process that is used: (a) to produce ammonia from nitrogen . …… [1] (b) to separate nitrogen from liquid air . …… [1] (c) to produce bromine from molten lead(II) bromide . …… [1] (d) to separate an undissolved solid from an aqueous solution . …… [1] (e) to produce amino acids from proteins . …… [1] (f) to separate a mixture of amino acids. . …… [1] [Total: 6]

Question

Complete the table to: ● deduce the number of protons, electrons and neutrons in the magnesium atom and copper ion shown ● identify the atom or ion represented by the final row. number of number of number of protons electrons neutrons 12Mg 25 12 29Cu 65 2+ 36 17 18 20 [Total: 5]

Question

Potassium reacts with chlorine to form potassium chloride, KCl. (a) Write a chemical equation for this reaction. . …… [2] (b) Potassium chloride is an ionic compound. Complete the diagram to show the electron arrangement in the outer shells of the ions present in potassium chloride. Give the charges on both ions. K Cl [3] (c) Molten potassium chloride undergoes electrolysis. (i) State what is meant by the term electrolysis. . …… . …… [2] (ii) Name the products formed at the positive electrode (anode) and negative electrode (cathode) when molten potassium chloride undergoes electrolysis. anode . …… cathode . …… [2] (d) Concentrated aqueous potassium chloride undergoes electrolysis. (i) Write an ionic half-equation for the reaction at the negative electrode (cathode). . …… [2] (ii) Name the product formed at the positive electrode (anode). . …… [1] (iii) Name the potassium compound that remains in the solution after electrolysis. . …… [1] (e) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of chlorine, Cl 2. Show the outer electrons only. Cl Cl [1] (f) The melting points and boiling points of chlorine and potassium chloride are shown. melting point boiling point / °C / °C chlorine –101 –35 potassium chloride 770 1500 (i) Deduce the physical state of chlorine at –75 °C. Use the data in the table to explain your answer. physical state . …… explanation …… . …… [2] (ii) Explain, in terms of structure and bonding, why potassium chloride has a much higher melting point than chlorine. Your answer should refer to the: ● types of particle held together by the forces of attraction ● types of forces of attraction between particles ● relative strength of the forces of attraction. . …… . …… . …… . …… . …… [3] [Total: 19]

Question

Dinitrogen tetroxide, N2O4, decomposes into nitrogen dioxide, NO2. The reaction is reversible. N2O4(g) 2NO2(g) colourless gas brown gas A gas syringe containing a mixture of dinitrogen tetroxide and nitrogen dioxide gases was sealed and heated. After reaching equilibrium the mixture was a pale brown colour. mixture of dinitrogen tetroxide and nitrogen dioxide end sealed plunger (a) State what is meant by the term equilibrium. . …… . …… . …… [2] (b) The plunger of the gas syringe is pushed in. The temperature does not change. The mixture initially turns darker brown. After a few seconds the mixture turns lighter brown because the equilibrium shifts to the left. N2O4(g) 2NO2(g) colourless gas brown gas (i) Explain why the mixture initially turns darker brown. . …… [1] (ii) Explain why the position of equilibrium shifts to the left. . …… [1] (c) The forward reaction is endothermic. (i) State what happens to the position of equilibrium when the temperature of the mixture is increased. . …… [1] (ii) State what happens to the rate of the forward reaction and the rate of the backward reaction when the temperature of the mixture is increased. rate of the forward reaction . …… rate of the backward reaction …… [2] [Total: 7]

Question

This question is about salts. (a) Salts that are insoluble in water are made by precipitation. ● Lead(II) iodide, PbI2, is insoluble in water. ● All nitrates are soluble in water. ● All sodium salts are soluble in water. You are provided with solid lead(II) nitrate, Pb(NO3)2, and solid sodium iodide, NaI. Describe how you would make a pure sample of lead(II) iodide by precipitation. Your answer should include: ● practical details ● a chemical equation for the precipitation reaction. . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… [5] (b) Nitrates decompose when heated. (i) When hydrated zinc nitrate is heated, oxygen gas is given off. Describe a test for oxygen. test . …… observations …… [2] (ii) Complete the equation for the decomposition of hydrated zinc nitrate. 2Zn(NO3)2•6H2O → ……ZnO + ……NO2 + O2 + ……H2O[2] (c) Some sulfates are hydrated. When hydrated sodium sulfate crystals, Na2SO4•xH2O, are heated, they give off water. Na2SO4•xH2O(s) → Na2SO4(s) + xH2O(g) A student carries out an experiment to determine the value of x in Na2SO4•xH2O. step 1 Hydrated sodium sulfate crystals are weighed. step 2 The hydrated sodium sulfate crystals are then heated. step 3 The remaining solid is weighed. (i) Describe how the student can check that all the water has been given off. . …… . …… . …… [2] (ii) In an experiment, 1.61 g of Na2SO4•xH2O is heated until all the water is given off. The mass of Na2SO4 remaining is 0.71 g. [Mr: Na2SO4,142; H2O,18] Determine the value of x using the following steps. ● Calculate the number of moles of Na2SO4 remaining. …… mol ● Calculate the mass of H2O given off. …… g ● Calculate the number of moles of H2O given off. …… mol ● Determine the value of x. x = …… [4] [Total: 15]

Question

This question is about iron. (a) Iron is extracted from its main ore in a blast furnace. waste gases raw materials: coke, iron ore, limestone A B molten iron (i) Name the main ore of iron used in the blast furnace. . …… [1] (ii) Name the substance that enters the blast furnace at A. . …… [1] (iii) Name the substance that leaves the blast furnace at B. . …… [1] (iv) Give two reasons for using coke in the blast furnace. 1 . …… 2 . …… [2] (b) Another ore of iron is iron pyrites, FeS2. Iron pyrites contains the positive ion, Fe2+. Deduce the formula of the negative ion in FeS2. . …… [1] (c) Iron is a transition element. A list of properties of iron is shown. ● Iron is a good conductor of electricity. ● Iron forms soluble salts. ● Iron forms coloured compounds. ● Iron has variable oxidation states. ● Iron acts as a catalyst. ● Iron forms a basic oxide. (i) Give two properties from the list in which iron differs from Group I elements. 1 . …… 2 . …… [2] (ii) Give two properties from the list in which iron is similar to Group I elements. 1 . …… 2 . …… [2] (d) Steel consists mainly of iron. Iron forms rust when it reacts with water and oxygen. Magnesium blocks can be attached to the bottom of steel boats. The magnesium does not completely cover the steel. steel boat water containing magnesium dissolved oxygen blocks (i) Explain how the magnesium blocks prevent iron from rusting. . …… . …… . …… . …… [2] (ii) Explain why replacing the magnesium blocks with copper blocks will not prevent the bottom of the boat from rusting. . …… . …… [1] [Total: 13]

Question

Many organic compounds contain carbon, hydrogen and oxygen only. (a) An organic compound V has the following composition by mass. C, 48.65%; H, 8.11%; O, 43.24% Calculate the empirical formula of compound V. empirical formula = …… [3] (b) Compound W has the empirical formula CH4O and a relative molecular mass of 32. Calculate the molecular formula of compound W. molecular formula = …… [1] (c) Compounds X and Y have the same general formula. X and Y are both carboxylic acids. Compound X has the molecular formula C2H4O2. Compound Y has the molecular formula C4H8O2. (i) Deduce the general formula of compounds X and Y. . …… [1] (ii) Draw the structure of compound Y. Show all of the atoms and all of the bonds. Name compound Y. name . …… [3] (iii) Give the name used to describe a ‘family’ of similar compounds with the same general formula, similar chemical properties and the same functional group. . …… [1] (d) Propene is an unsaturated hydrocarbon. The formula of propene is shown. CH3CH=CH2 (i) State the colour change observed when propene is added to aqueous bromine. from …… to …… [1] (ii) Propene can be produced by cracking long chain alkanes. Pentadecane, C15H32, is cracked to produce an alkane and propene in a 1 : 2 molar ratio. Complete the chemical equation for this reaction. C15H32 → …… + …… [2] (iii) Propene can be converted into poly(propene). Name the type of polymerisation that occurs when propene is converted into poly(propene). . …… [1] (iv) Complete the diagram to show a section of poly(propene). C C C C [2] [Total: 15] 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.).