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Form 4 Electrochemistry Topical Questions and Answers

In this session, several Form 4 Electrochemistry Questions will be solved. Answers will be given in video format.

Lessons (52)

• 1.    Explain why it is not advisable to use aqueous sodium chloride solution as the salt bridge in the electrochemical cell formed between half cells,
  1m 29s

• 2.    (a)The diagram below shows incomplete set up of the laboratory preparation and collection of chlorine gas. Study it and answer the questions that follow. (i)Complete the set up to show how dry chlorine gas may be collected. (ii) The equation for the redox reaction that takes place is #MnO_2#(s)+4 HCL(aq)#toMnCl_2#(aq)+#2H_2O#(l)+#Cl_2# (g) Explain, using oxidation numbers, which species is reduced
  15m 37s

• 3.    Aqueous potassium sulphate was electrolyzed using platinum electrodes in a cell. (a)Name the products formed at the cathode and anode. (b) How does the concentration of the electrolyte change during electrolysis? (c ) Why would it not be advisable to electrolyse aqueous potassium sulphate using potassium metal electrodes?
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• 4.    Use standard electrode potentials for elements A, B, C, D and F given below to answer the questions that follow. The letters do not represent the actual symbols of the elements. (i) Which element is likely to be hydrogen? Give a reason for your answer. (ii) What is the# E^?# value of the strongest reducing agent? (iii) In the space provided, draw a labelled diagram of the electrochemical cell that
  15m 30s

• 5.    Use the information below to answer the questions that follow: (a)Calculate the #E^?# value for the electrochemical cell represented below. Al(s) |Al3+(aq)?Fe2+(aq)|Fe(s) (b)Give a reason why aluminum metal would protect iron from rusting better than zinc metal.
  2m 43s

• 6.    The set-up below was used to electrolyse aqueous copper (II) sulphate. (a) Explain why the bulb light brightly at the beginning of the experiment becomes dim after sometime. (b) Write the ionic equation of the reaction that took place at the cathode.
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• 7.    Use the cell representation below to answer the questions that follow. Cr(s)|#Cr^(3+)(aq)?Fe^(2+)(aq)# |Fe(s) (a) Write the equation for the cell reaction. (b) If the e.m.f of the cell is 0.30 volts and the #E^?# value for #Fe^(2+)(aq)#|Fe(s) is -0.44 volts, calculate the #E^?# value for# Cr^(3+)(aq)|Cr(s)#
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• 8.    The set-up below was used during the electrolysis of aqueous magnesium sulphate using inert electrodes. (a) Name a suitable pair of electrodes for this experiment. (b) Identify the anions and cations in the solution. (c) On the diagram, label the cathode. (d) Write ionic equations for the reactions that took place at the: Anode: Cathode: (e) Explain the change that occurred to the concentration of
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• 9.    When a current of 1.5 amperes was passed through a cell containing #M^(3+)# ions of metal M for 15 minutes, the mass of the cathode increased by 0.26 g. (1 Faraday =96500 coulombs). (a) Calculate the quantity of electricity used. (b) Determine the relative atomic mass of metal M.
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• 10.    (a)The diagram below represents a mercury cell that can be used in the industrial manufacture of sodium hydroxide. Study it and answer the questions that follow. (i) Name I.the raw material introduced at 2. II.another substance that can be used in the cell instead of graphite. (ii) Identify the by-product that comes out at 1. (iii) Give I.one use of sodium hydroxide. II.two reasons why mercury is
  8m 56s

• 11.    An element P has a relative atomic mass of 88. When a current of 0.5 amperes was passed through the fused chloride of P for 32 minutes and 10 seconds, 0.44 g of P were deposited at the cathode. Determine the charge on an ion of P. (1 Faraday =96500 Coulombs).
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• 12.    (a) Study the standard electrode potentials for the half-cells given below and answer the questions that follow. (The letters do not represent the actual symbols of the elements.) (i) Identify the strongest oxidizing agent. Give a reason for your answer. (ii) Which two half-cells would produce the highest potential difference when combined? (iii) Explain whether the reaction represented below can
  11m 57s

• 13.    The set-up below was used to electroplate a metallic spoon. Study it and answer the questions that follow. (a) Write an ionic equation for the reaction that occurred at the cathode. (b) State and explain what happened to the anode.
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• 14.    Study the flow chart below and answer the questions that follow: (a) Identify substance: (i) A (ii) B (b) Name process C. (c) Give one use of PVC. (d) Write an ionic equation for the reaction in which chlorine gas is produced. (e) State and explain the observation that would be made if chlorine gas was bubbled into an aqueous solution of sodium iodide. (f) In the preparation of a bleaching agent
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• 15.    The table below gives standard electrode potentials for the metals represented by the letters D,E, F and G. Study it and answer the questions that follow. (a) Which metal can be displaced from a solution of its salt by all the other metals in the table? Give a reason. (b) Metals F and G were connected to form a cell as shown in the diagram below. (i) Write the equation for the reactions that occur
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• 16.    During purification of copper by electrolysis, 1.48g of copper were deposited when current was passed through aqueous copper (II) sulphate for 212 hours. Calculate the amount of current used. (Cu=63.5; 1F=96500 C).
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• 17.    The diagram below is a cross-section of a dry cell. Study it and answer the questions that follow. (a) One the diagram, show with a (+) sign the positive terminal. (b) (i) Write the equation for the reaction in which electrons are produced. (ii) The zinc can is lined with ammonium chloride and zinc chloride paste. What would happen if solid mixture was used. Explain.
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• 18.    A strip of metal Q was dipped into a solution of copper (II) sulphate and allowed to stand overnight. Given that: (a)State the observations which were made. (b) Give a reason for your answer in (a) above.
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• 19.    The diagram below represents the set-up that was used to study the effect of an electric current on pure water and dilute sulphuric (VI) acid. State and explain the observation made when each experiment was started.
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• 20.    (a)Brine usually contains soluble calcium and magnesium salts. Explain how sodium carbonate is used to purify brine. (b) The diagram below represents a diaphragm cell used to electrolyse pure brine (i) Write the equations for the reactions that take place at I.Cathode II. Anode (ii) Name: I. product at U. II. another material that can be used instead of titanium III.the impurity present in the
  4m 21s

• 21.    When a current of 0.82 A was passed for 5 hours through an aqueous solution of metal Z,2.65 g of the metal were deposited. Determine the charge on the ions of metal Z. (1 Faraday =96500 Coulombs: Relative atomic mass of Z=52
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• 22.    (a) The table below shows the standard reduction potentials for four half-cells. Study it and answer the questions that follow. (Letters are not the actual symbols of the elements)
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• 23.    Study the standard reduction potentials given below and answer the questions that follow. (The letters are not the actual symbols of the elements). (a)The standard reduction potential for #Fe^(2+)(aq)# is -0.44 volts. Select the element which would best protect iron from rusting.
  3m 2s

• 24.    (a) What is an electrolyte? (b) State how the following substances conduct electricity: (i) Molten calcium chloride (ii) Graphite. (c ) The diagram below shows a set up that was used to electrolyze aqueous magnesium sulphate. (i) On the diagram above, using an arrow, show the direction of flow of electrons. (ii) Identify the syringe in which hydrogen gas would be collected. Explain. (d)Explain why
  8m 33s

• 25.    (a)In an experiment to determine the molar heat of reaction when magnesium displaces copper, 0.15 g of magnesium powder were added to #25.0cm^3# of 2.0M copper (II) chloride solution. The temperature of copper (II) chloride solution was #25^0C#,while that of the mixture was #43^0C#. (i) Other than increase in temperature, state and explain the observations which were made during the reaction.
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• 26.    (a)Use the information given below to draw a labeled diagram of an electrochemical cell that can be constructed to measure the electromotive force between G and J. (b)Calculate the #E^?# value for the cell constructed in (a)above.
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• 27.    (a)When brine is electrolyzed using inert electrodes, chlorine gas is liberated at the anode instead of oxygen. Explain this observation. (b) Name the product formed at the cathode.
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• 28.    During the electrolysis of aqueous silver nitrate, a current of 5.0A was passed through the electrolyte for 3 hours. (a) Write the equation for the reaction which took place at the anode. (b) Calculate the mass of silver deposited. (Ag=108;1F=96500C)
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• 29.    The following are half-cell reactions and their reduction potentials. (a) Write the cell representation for the electrochemical cell that would give the highest #E^?# (b) State and explain the observations made when a copper rod is placed in a beaker containing silver nitrate solution.
  3m 27s

• 30.    The diagram below represents an experiment that was set up to investigate movement of ions during electrolysis. When the circuit was completed, it was noticed that a blue colour spread towards the right. (a) Explain this observation. (b) Write the equation for the reaction that occurred at the anode.
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• 31.    The diagram below represents a set up that can be used to electrolyze aqueous copper (II) sulphate. (a) (i) Describe how oxygen gas is produced during the electrolysis. (ii) explain why copper electrodes are not suitable for this electrolysis (b) Impure copper is purified by an electrolytic process. (i) Name one ore from which copper is obtained
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• 32.    When aluminium oxide was electrolysed, 1800kg of aluminium metal were obtained. a) Write equation for the formation of aluminium metal b) Calculate the quantity of electricity in faradays used (Al=27)
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• 33.    Hydrogen and oxygen can be obtained by electrolysis of acidified water. Using equations for the reactions at the electrodes, explain why the volume of hydrogen obtained is twice that of oxygen.
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• 34.    The standard reduction potentials of two half –cells are: Ag+(aq) + eAg(s) ; E = 0.80V 2H2O (l) + 2eH2 (g) + 2OH (aq); E1 = 0.83V Draw a labeled diagram of an electrochemical cell that can be constructed using the two half – cells
  3m 7s

• 35.    The set-up below (figure 2) was used to electrolyse a bromide of metal D, DBr2. i) Write equation for the reactions at the I cathode II anode (b) The electrodes used in the experiment were made of carbon and metal D. which of the two electrodes was used as the anode? Give a reason. (c) Give a reason why this experiment is carried out in a fume cupboard.
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• 36.    Complete the table below by writing the products formed at the electrodes during the electrosis of the electrolytes given in the table.
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• 37.    The half equations involved in a cell are: (a) Write the overall equation for the electrochemical cell. (b) Calculate the e.m.f. generated by a battery consisting of ten cells. (c) State one environmental advantages of using these cells in spacecrafts.
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• 38.    (a) Which one of the following compounds; Urea, ammonia, sugar and copper (II) chloride will conduct an electric current when dissolved in water? Give a reason. (b) The diagram below shows an electrochemical cell. Study it and answer the questions that follow. Given the following: #Fe^(2+)# (aq) +2e?Fe(s);E?= -0.44V #Zn^(2+)# (aq)+2e?Zn(s);E?= -0.76V (i) Show on the diagram using an arrow, the
  6m 26s

• 39.    Sodium hydroxide can be prepared by the following methods; I and II. (a) Name one precaution that needs to be taken in method I. (b) Give the name of process A. (c) Give one use of sodium hydroxide.
  1m 9s

• 40.    The set-up below was used by a student to investigate the products formed when aqueous copper (II) chloride was electrolyzed using carbon electrodes. (a) (i) Write the equation for the reaction that takes place at the cathode. (ii) Name and describe a chemical test for the product initially formed at the anode when a highly concentrated solution of copper (II) chloride is electrolyzed.
  7m 11s

• 41.    Below is a representation of an electrochemical cell. Pb(s) / #Pb^(2+)# (aq) // #Ag^(+)# (aq)/ Ag(s). (a) What does // represent? (b) Given the following: #Pb^(2+)# (aq) + 2e ? Pb (s); - 0.13 #Ag^(2+)# (aq) + e ? Ag (s); + 0.80 Calculate the E.M.F. of the electrochemical cell.
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• 42.    (a) The set up below was used to investigate the products formed at the electrodes during electrolysis of aqueous magnesium sulphate using inert electrodes. Use it to answer the questions that follow. (i) During the electrolysis, hydrogen gas was formed at electrode Y. Identify the anode. Give a reason for your answer. (ii) Write the equation for the reaction which took place at electrode X.
  4m 7s

• 43.    (a) A student electroplated a spoon with copper metal. Write an equation for the process that took place at the cathode. (b) Calculate the time in minutes required to deposit 1.184g of copper if a current of 2 amperes was used. (1 Faraday = 96500 coulombs, Cu = 63 .5).
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• 44.    (a) The set up below can be used to produce sodium hydroxide by electrolyzing brine. (i) Identify gas Y. (ii) Describe how aqueous sodium hydroxide is formed in the above set-up. (iii) One of the uses of sodium hydroxide is in the manufacturing of soaps. State one other use of sodium hydroxide. (b) Study the information given in the table below and answer the questions that follow.
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• 45.    (a) A student electrolyzed dilute sodium chloride solution using inert carbon electrodes. Name the products at: (i) Anode; (ii) Cathode. (b) If the experiment was repeated using concentrated sodium chloride instead of dilute sodium chloride solution, write the half equation at the anode.
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• 46.    Dilute sulphuric (VI) acid was electrolysed using platinum electrodes. Name the product formed at the anode and give a reason for your answer.
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• 47.    Study the standard electrode potentials in the table below and answer the questions that follow. (a) Which of the metals is the strongest reducing agent? (b) What observations will be made if a silver coin was dropped into an aqueous solution of copper (II) sulphate? Explain.
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• 48.    (a) The diagram below represents a dry cell. Use it to answer the questions that follow. (i) Which of the letters represent: (I) Carbon electrode? (II) The electrolyte? (ii) One of the substances used in a dry cell is manganese (IV) oxide. State two roles of manganese (IV) oxide in the dry cell.
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• 49.    The diagram in Figure 1 shows a section of a dry cell. Study it and answer the questions that follow. (a) Name the part labeled B. (b) The part labeled A is a paste. Give a reason why it is not used in dry form. (c) What is the purpose of the zinc container?
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• 50.    Table 1. Use it to answer the questions that follow. (a) (i) Identify a substance that is a metal. Give a reason. (ii) Substance F does not conduct electricity in solid state but conducts in molten or aqueous state. Explain. (b) Copper (II) sulphate solution was electrolyzed using the set up in Figure 1. (i) State the observations made during electrolysis. (ii) Write the equation for the reaction
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• 51.    Metal X and Y have standard electrode potentials of -0.13V and -0.76V respectively. The metals were connected to form a cell as shown in Figure 4. (a) Name the part labeled Z. (b) State one function of the part labeled Z. (c) Calculate the e.m.f. of the cell.
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• 52.    Given that #E^(?)# of Cu(s) /#Cu2^(+)# (aq) is +0.34V and that of Zn(s) /#Zn^(2+)# (aq) is -0.76V, draw a labeled diagram of zinc and copper electrochemical cell.
  2m 42s