4. Electrochemistry
A section of Chemistry, 0620
Listing 10 of 500 questions
Magnesium is manufactured by the electrolysis of molten magnesium chloride. The negative electrode is made of iron. Suggest a non-metal which could be used for the positive electrode. Give a reason for your answer. Predict the products of the electrolysis of molten magnesium chloride at: the positive electrode the negative electrode.  The following statements are about the procedure for making crystals of hydrated magnesiumchloride from magnesium and dilute hydrochloric acid. A Leave the mixture until no more bubbles are seen. B Leave the mixture at room temperature to form more crystals. C Add an excess of magnesium to dilute hydrochloric acid. D Warm the filtrate to the point of crystallisation. E Filter off the crystals and dry between filter papers. F Filter off the excess magnesium. Put the statements A, B, C, D, E and F in the correct order. The first one has been done for you. C  Magnesium is a metal in GroupII of the PeriodicTable. Copper is a transition element. Copper has a higher melting point and a higher boiling point than magnesium. Describe two other properties of copper which are different from those of magnesium.  Chromatography can be used to separate a mixture of ions from different transition element compounds. Four samples, R, S, T and U, each containing transition element ions, were placed on a piece of chromatography paper. Two solutions, Y and Z, each containing only one type of transition element ion were also placed on the same piece of chromatography paper. The results of the chromatography are shown. R S T U Y Z Which sample, R, S, T or U, contains the same ions as both solutionY and solutionZ? Which sample, R, S, T or U, does not contain the same ions as either solution Y or solutionZ? In which sample, R, S, T or U, has the greatest number of transition element ions been separated? 
0620_w19_qp_31
THEORY
2019
Paper 3, Variant 1
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Dilute hydrochloricacid, HCl , reacts with aqueous sodiumcarbonate, Na2CO3. The chemical equation for the reaction is shown. 2HCl + Na2CO3 2NaCl + CO2 + H2O A 25.0 cm3 portion of Na2CO3was placed in a conical flask with a few drops of a suitable indicator. It was titrated against HCl of concentration 0.180 mol / dm3. 20.0 cm3 of HCl was required to reach the end-point. Calculate the concentration of the Na2CO3, 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.  mol ● ● Calculate the concentration of the Na2CO3in mol / dm3.  mol / dm3  In another experiment, the volume of carbondioxide, CO2, produced was 48.0 cm3, measured at room temperature and pressure. How many moles of CO2 is this?  moles of CO2 = mol A sample of concentrated hydrobromic acid, HBr, was electrolysed using platinum electrodes. The concentration of the hydrobromic acid was 8.89 mol / dm3. Calculate the concentration of the HBrin g / dm3.  concentration of HBr= g / dm3 Explain why concentrated HBrcan conduct electricity. Magnesium is not a suitable material from which to make the electrodes. Explain why. Predict the product formed at the anode when concentrated HBris electrolysed. Write the ionic half-equation for the reaction occurring at the cathode. 
0620_w19_qp_41
THEORY
2019
Paper 4, Variant 1
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Electrolysis is used to extract metals from metal compounds. Describe the electrolysis of molten lead(bromide. In your answer include: ● ● a labelled diagram of the apparatus used ● ● the names of the products formed at the positive and the negative electrodes. positive electrode negative electrode  Use the kinetic particle model to describe the arrangement and motion of the particles in molten lead. arrangement motion  Lead is a metal which is soft and has a relatively low melting point. State two other physical properties of metals such as lead.  Lead is formed when red leadoxide, Pb3O4, is heated with carbon. Pb3O4 + 4C → 3Pb + 4CO Explain how this equation shows that Pb3O4 has been reduced. 
0620_w20_qp_31
THEORY
2020
Paper 3, Variant 1
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Electrolysis is used to extract reactive metals from metal compounds. Describe the electrolysis of molten sodiumchloride. In your answer include: ● ● a labelled diagram of the apparatus used ● ● the observations made at the positive and the negative electrode. observation at positive electrode observation at negative electrode  Use the kinetic particle model to describe the arrangement and separation of the particles in solid sodium. arrangement separation  Sodium is a metal in Group I of the Periodic Table. Iron is a transition element. Give two ways in which the physical properties of iron differ from the physical properties of sodium.  The chemical equation for the reaction between iron(oxide and carbonmonoxide is shown. Fe2O3 + 3CO → 2Fe + 3CO2 Explain how this equation shows that carbonmonoxide has been oxidised. 
0620_w20_qp_32
THEORY
2020
Paper 3, Variant 2
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Dilute sulfuricacid is electrolysed using the apparatus shown in the diagram. power supply inert electrodes dilute sulfuric acid + – State what is meant by the term electrolysis. Explain why inert electrodes are used. Name the products formed at each electrode. negative electrode positive electrode  Write an ionic half‑equation for the reaction at the negative electrode. Sulfuric acid is manufactured using the Contact process. This manufacture involves four stages. Stage1 involves the combustion of sulfur to form sulfurdioxide. Write the chemical equation for stage1. The equation for stage2 is shown. 2SO2+ O22SO3The reaction can reach equilibrium. Explain what is meant by the term equilibrium. The energy level diagram for the forward reaction in stage2 is shown. energy progress of reaction 2SO2+ O22SO3Explain what the diagram shows about the energy changes in the forward reaction. In stage3 sulfurtrioxide, SO3, is converted to oleum, H2S2O7. In stage4 oleum reacts to form sulfuricacid, H2SO4. State what oleum reacts with in stage4. A sample of sulfuricacid, H2SO4, has a concentration of 0.75 mol / dm3. Calculate the concentration of sulfuric acid in g / dm3.  g / dm3 
0620_w20_qp_41
THEORY
2020
Paper 4, Variant 1
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Questions Discovered
500