4. Electrochemistry
A section of Chemistry, 0620
Listing 10 of 500 questions
The table gives some chemical properties of transition elements and their compounds, and of GroupI elements and their compounds. chemical property transition elements GroupI elements ability to act as catalysts yes no exist as coloured compounds yes no What is meant by the term catalyst? Give one other chemical property shown by transition elements which is not shown by GroupI elements. Give two physical properties shown by transition elements which are not shown by GroupI elements.  The energy level diagram shows the energy profile for the reaction between zinc and dilute sulfuricacid. energy progress of reaction Zn+ H2SO4Complete the diagram by adding the formulae of the products. Include state symbols. Draw an arrow on the diagram to represent the activation energy. Is the reaction endothermic or exothermic? Explain your answer. The reaction between zinc and dilute sulfuricacid can be catalysed by the addition of aqueous copper(sulfate. On the diagram, add the energy profile for the catalysed reaction. energy progress of reaction Zn+ H2SO4 A student electrolyses aqueous copper(sulfate using the apparatus shown. + – carbon electrodes aqueous copper(sulfate power supply Oxygen gas forms at the positive electrode . Write an ionic half‑equation for the reaction at the negative electrode . Include state symbols. Describe what the student observes at the negative electrode. Give two other observations which the student makes during the electrolysis.  What difference would the student observe at the positive electrode if the aqueous copper(sulfate were replaced by concentrated aqueous copper(chloride? 
0620_s18_qp_41
THEORY
2018
Paper 4, Variant 1
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Potassium reacts with bromine at room temperature to form potassium bromide. Write a chemical equation for this reaction. Include state symbols. Potassiumbromide exists as an ioniclattice. Potassiumbromide does not conduct electricity when solid but does conduct electricity when molten. What is meant by the term ionic lattice? Explain why potassium bromide does not conduct electricity when solid but does conduct electricity when molten. Concentrated aqueous potassium bromide is an electrolyte. What is meant by the term electrolyte? Describe the electrolysis of concentrated aqueous potassium bromide. Include: ● ● an ionic half-equation for the reaction at the cathode ● ● the name of the product at the anode ● ● the name of the potassium compound formed. When molten potassium bromide is electrolysed, the product at the cathode is different. Name the product at the cathode when molten potassiumbromide is electrolysed. Iodine reacts with chlorine to form iodine monochloride, ICl, as the only product. Write a chemical equation for this reaction. Draw a dot-and-cross diagram to show the electron arrangement in a molecule of iodinemonochloride. Show outer shell electrons only. Potassiumbromide has a melting point of 734 °C. Iodinemonochloride has a melting point of 27 °C. In terms of attractive forces, explain why there is a large difference between these melting points. When chlorine gas is passed through aqueous potassium bromide, a redox reaction occurs. The ionic equation is shown. Cl 2 + 2Br – 2Cl – + Br2 Write an ionic half-equation showing what happens to the chlorine molecules, Cl 2, in this reaction. Explain why the bromide ions, Br –, act as reducing agents in this reaction.
0620_s18_qp_42
THEORY
2018
Paper 4, Variant 2
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Nickel(iodide crystals are hydrated. A sample of hydrated nickel(iodide crystals has the following composition by mass: Ni, 14.01%; I, 60.33%; H, 2.85%; O, 22.81%. Calculate the empirical formula of the hydrated nickel(iodide crystals.  empirical formula = Molten nickel(iodide can be electrolysed using the apparatus shown. copper wires power supply platinum electrodes molten nickel(iodide During electrolysis, charge is transferred through the copper wires and through the molten nickel(iodide. Name the type of particles which transfer charge through the copper wires. Name the type of particles which transfer charge through the molten nickel(iodide. Predict the products of the electrolysis of molten nickel(iodide. Write an ionic half-equation for the formation of one of these products. products ionic half-equation  A student electrolysed copper(sulfate solution using the two sets of apparatus shown. apparatus A carbon electrodes copper(sulfate solution apparatus B copper electrodes copper(sulfate solution power supply power supply In apparatusA the student used carbon electrodes. In apparatusB the student used copper electrodes. The student made the following observations. apparatus A apparatus B The mass of the negative electrode increased. The mass of the negative electrode increased. The mass of the positive electrode stayed the same. The mass of the positive electrode decreased. Bubbles were seen at the positive electrode. No bubbles were seen at the positive electrode. Explain why the mass of the negative electrode increased in both sets of apparatus. Name the gas that formed the bubbles seen in apparatusA. Explain why the mass of the positive electrode decreased in apparatusB. Suggest what happens to the colour of the solution in apparatusA and apparatusB as the electrolysis progresses. Explain your answer. colour of the solution in apparatus A colour of the solution in apparatus B explanation 
0620_s18_qp_43
THEORY
2018
Paper 4, Variant 3
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Displacement reactions occur between metals and metal ions. Displacement reactions can be used to determine the order of reactivity of metals such as lead (Pb), nickel (N, and silver (Ag). The ionic equation for a displacement reaction is shown. Ni+ Pb2+Pb+ Ni2+The ionic half-equations for this reaction are shown. NiNi2++ 2e– Pb2++ 2e– PbThe ionic half-equations show that electrons are donated by nickel atoms and accepted by lead ions. Identify the reducing agent in the displacement reaction. Give a reason for your answer. reducing agent reason  What is the general term given to the type of reaction in which electrons are transferred from one species to another? The ionic equation for another displacement reaction is shown. Pb+ 2Ag+2Ag+ Pb2+Write the two ionic half-equations for this reaction.  Use the information in and to put the three metals lead, nickel and silver in order of reactivity. most reactive least reactive  Nickel is a transition element. Nickel is stronger than sodium. Describe two other differences in the physical properties of nickel and sodium.  Predict one difference in the appearance of aqueous solutions of nickel compounds compared to aqueous solutions of sodium compounds. Copper is refined by electrolysis. Nickel can be refined using a similar method. The diagram shows the refining of nickel by electrolysis. Complete the labels in the boxes. power supply + – cathode made of electrolyte of anode made of  Indicate, by writing N on the diagram, where nickel is produced. 
0620_s19_qp_42
THEORY
2019
Paper 4, Variant 2
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Solutions of ionic compounds can be broken down by electrolysis. Concentrated aqueous copper(chloride was electrolysed using the apparatus shown. power supply + – anode made of platinum concentrated aqueous copper(chloride cathode made of platinum The ionic half-equations for the reactions at the electrodes are shown. negative electrode: Cu2++ 2e– Cupositive electrode: 2Cl –Cl 2+ 2e– Platinum is a solid which is a good conductor of electricity. State one other property of platinum which makes it suitable for use as electrodes. State what would be seen at the positive electrode during this electrolysis. State and explain what would happen to the mass of the negative electrode during this electrolysis. The concentrated aqueous copper(chloride electrolyte is green. Suggest what would happen to the colour of the electrolyte during this electrolysis. Explain your answer. Identify the species that is oxidised during this electrolysis. Explain your answer. species that is oxidised explanation  Metal objects can be electroplated with silver. Describe how a metal spoon can be electroplated with silver. Include: ● what to use as the positive electrode and as the negative electrode ● what to use as the electrolyte ● an ionic half-equation to show the formation of silver. You may include a diagram in your answer. ionic half-equation  Give one reason why metal spoons are electroplated with silver. 
0620_s19_qp_43
THEORY
2019
Paper 4, Variant 3
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Questions Discovered
500