2 1 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] © UCLES 2021 0620/41/M/J/21
3 2 Complete the table to: ● educe the number of protons, electrons and neutrons in the magnesium atom and copper ion d 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] © UCLES 2021 0620/41/M/J/21 [Turn over
4 3 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] © UCLES 2021 0620/41/M/J/21
5 (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] © UCLES 2021 0620/41/M/J/21 [Turn over
6 4 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] © UCLES 2021 0620/41/M/J/21
7 5 This question is about salts. (a) Salts that are insoluble in water are made by precipitation. ● Lead(II) iodide, PbI2, is insoluble in water. ● ll nitrates are soluble in water. A ● 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] © UCLES 2021 0620/41/M/J/21 [Turn over
8 (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] © UCLES 2021 0620/41/M/J/21
9 (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] © UCLES 2021 0620/41/M/J/21 [Turn over
10 6 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] © UCLES 2021 0620/41/M/J/21
11 (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] © UCLES 2021 0620/41/M/J/21 [Turn over