Chemistry 0620/41 October/November 2024: question paper and mark scheme

Question

A list of chemical and physical processes, A to H, is shown. A combustion B diffusion C melting D neutralisation E photosynthesis F reversible reaction G roasting H thermal decomposition Answer the following questions about processes A to H. Each letter may be used once, more than once or not at all. State which of the processes A to H: (a) happens when an acid reacts with an alkali …… [1] (b) reaches a position of equilibrium …… [1] (c) involves particles changing from fixed positions to being mobile, but still touching …… [1] (d) are physical changes …… and …… [1] (e) is caused by gas particles colliding with each other. …… [1] [Total: 5]

Question

This question is about atomic structure and the Periodic Table. (a) Define the term nucleon number. …… [1] (b) State the connection between the number of occupied electron shells in an atom and the period number of that element. …… [1] (c) Write the electronic configuration of the following atom and ion. 28 14Si …… 37 – 17Cl …… [2] (d) Complete Table 2.1. Table 2.1 number of number of number of atom or ion protons neutrons electrons 23 11Na 11 19 – 9F 9 10 31 38 28 [5] (e) A sample of thallium, Tl, contains two isotopes, 203 Tl and 205 Tl. (i) Define the term isotopes. …… [2] (ii) The relative abundance of 203 Tl : 205Tl is in the ratio 3 : 7. Calculate the relative atomic mass of thallium in the sample to one decimal place. relative atomic mass = …… [2] (iii) Suggest why these two isotopes have identical chemical properties. …… [1] [Total: 14]

Question

Copper(II) sulfate has the formula CuSO4. Aqueous copper(II) sulfate is a blue solution. A sample of aqueous copper(II) sulfate is made by adding excess copper(II) oxide, CuO, to hot dilute sulfuric acid, H2SO4. (a) Complete the symbol equation for this reaction. Include state symbols. CuO(……) + H2SO4(……) → CuSO4(……) + ……(l) [2] (b) State one observation which shows that copper(II) oxide is added in excess. …… [1] (c) Describe how aqueous copper(II) sulfate can be separated from the reaction mixture. …… [1] (d) Crystals of hydrated copper(II) sulfate can be obtained from aqueous copper(II) sulfate by crystallisation. (i) State what is meant by the term hydrated. …… [1] (ii) Write the formula of hydrated copper(II) sulfate. …… [1] (iii) Describe how this crystallisation is done. …… [2] (e) Aqueous copper(II) sulfate undergoes electrolysis using graphite electrodes. (i) State why aqueous copper(II) sulfate conducts electricity. …… [1] (ii) Give two reasons why the electrodes are made of graphite. 1 …… 2 …… [2] (iii) Describe how the appearance of the electrolyte changes during the electrolysis of aqueous copper(II) sulfate. …… [1] (iv) Describe what is seen at the cathode during the electrolysis of aqueous copper(II) sulfate. …… [1] (v) Write the ionic half-equation for the reaction at the anode. …… [3] (vi) State two differences seen if the electrolysis is repeated using copper electrodes instead of graphite electrodes. 1 …… 2 …… [2] [Total: 18]

Question

When magnesium nitrate is heated strongly, magnesium oxide is formed. (a) The equation for this reaction is shown. 2Mg(NO3)2 → 2MgO + 4NO2 + O2 (i) State the change in oxidation number of nitrogen, N, in this reaction. from …… to …… [2] (ii) Identify the element which is oxidised in this reaction. …… [1] (iii) Calculate the volume of NO2 gas, at r.t.p., formed when 7.40 g of Mg(NO3)2 is heated. Use the following steps. ● Calculate the Mr of Mg(NO3)2. ● Calculate the number of moles of Mg(NO3)2 used. …… mol ● Determine the number of moles of NO2 formed. …… mol ● Calculate the volume of NO2 gas, in cm3, at r.t.p. …… cm3 [4] (b) Magnesium oxide, MgO, is an ionic compound. Complete the dot-and-cross diagram in Fig. 4.1 of the ions in magnesium oxide. Give the charges on each of the ions. Mg O Fig. 4.1 [3] (c) Oxygen is a covalent molecule. Complete the dot-and-cross diagram in Fig. 4.2 of a molecule of oxygen. The inner shells have been drawn. O O Fig. 4.2 [2] [Total: 12]

Question

Hydrogen is the first element of the Periodic Table. (a) Hydrogen is used in fuel cells to produce electricity in vehicles. (i) Name the substance which combines with hydrogen in a fuel cell. …… [1] (ii) Give one advantage and one disadvantage of using fuel cells instead of gasoline in vehicle engines. advantage …… disadvantage …… [2] (b) Hydrogen gas can be made from petroleum by a two-step procedure. step 1 Petroleum is separated into different components. step 2 Large molecules obtained in step 1 are converted into smaller molecules including hydrogen gas. (i) Name the process used in step 1. …… [1] (ii) Name the process used in step 2. …… [1] (c) Organic compounds contain hydrogen atoms. Calculate the number of hydrogen atoms in 44.0 g of the ester methyl propanoate, CH3CH2COOCH3. One mole of CH3CH2COOCH3 contains 6.02 × 1023 molecules. number of hydrogen atoms = …… [4] (d) For each of the homologous series shown, name a member that contains six hydrogen atoms. ● alkanes …… ● alkenes …… ● alcohols …… ● carboxylic acids …… [4] (e) Unsaturated alkenes are converted into saturated alkanes by reaction with hydrogen gas. (i) State why alkenes and alkanes are hydrocarbons. …… [1] (ii) State why alkenes are unsaturated. …… [1] (iii) Name the catalyst needed to convert alkenes into alkanes. …… [1] (iv) Explain why the conversion of alkenes into alkanes is an addition reaction. …… [1] [Total: 17]

Question

Natural polyamides are polymers made from amino acid monomers. (a) State the type of polymerisation reaction that occurs when natural polyamides form. …… [1] (b) State the term given to natural polyamides. …… [1] (c) An amino acid is represented as shown in Fig. 6.1. H 2N COOH Fig. 6.1 Complete Fig. 6.2 to show the general structure of an amino acid. Show all of the atoms and all of the bonds in the functional groups. C H Fig. 6.2 [3] (d) Three different amino acids are represented as shown in Fig. 6.3. amino acid A amino acid B amino acid C H 2N COOH H 2N COOH H2 N COOH Fig. 6.3 Complete the diagram in Fig. 6.4 to show the part of the structure of the natural polyamide that forms when the three amino acids, A, B and C, combine. Show all of the atoms and all of the bonds in the linkages. Fig. 6.4 [3] (e) A mixture of the three amino acids, A, B and C, can be separated and the amino acids identified using paper chromatography. Complete the equation for Rf. Rf = [2] (f) A sample of the mixture of the three amino acids, A, B and C, is placed onto the baseline and a chromatogram is allowed to develop as shown in Fig. 6.5. The finished chromatogram is shown in Fig. 6.6. mixture placed here baseline solvent Fig. 6.5 Fig. 6.6 The amino acids, A, B and C, are colourless. Water is used as the solvent. (i) Explain why the baseline is drawn in pencil. …… [1] (ii) State the type of substance used to make the colourless amino acids visible on the chromatogram in Fig. 6.6. …… [1] (iii) Explain why in Fig. 6.6 only two spots are seen from the mixture of three amino acids. …… [1] (iv) Suggest how the experiment can be changed to separate all three amino acids. …… [1] [Total: 14] 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 89–103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 actinoids Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og francium radium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium nihonium flerovium moscovium livermorium tennessine oganesson – – – – – – – – – – – – – – – – – 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.).