Set 3 Electrochemistry Perfect Score F Define the meaning of electrolyte and non-electrolyte and respective examples.

Transcription

1 Electrolysis 1. Define the meaning of electrolyte and non-electrolyte and respective examples. Meaning Electrolyte Non-electrolyte Example 2. Define electrolysis: 3. Energy change : Electrolysis:.... energy to energy. Voltaic cell:..energy to... energy. 4. Write the half equation to represent the discharge of anion and cation. Anion Half equation Cation Half equation Hydroxide Hydrogen ion, ion, OH - H + Chloride ion, Cl - Sodium ion, Na + Bromide ion, Silver ion, Ag + Br - Iodide ion, I - Oxide ion, O 2- Lead (II)ion, Pb 2+ Copper(II) ion, Cu 2+ Aluminium ion, Al Products of electrolysis depend on three factors, they are a)..... b). c). Chemistry Perfect Score Module Form Set 3 42

2 7. Complete the electrochemical series below. Cation K + Anion F - Ca 2+ Cl - Zn 2+ H + Ease of discharge increases Diagram: Electrochemical Series Chemistry Perfect Score Module Form Set 3 43

3 Sodium nitrate solution, 0.5 mol dm -3 Carbon electrodes Electrolysis of sodium nitrate solution. 8. Describe the electrolysis of sodium nitrate solution using carbon electrodes. Anode Cathode Write the formula of all ions present in the electrolyte. Write the formula of ion/ions which is/are attracted to anode and cathode. Which is selectively discharged? Give a reason. Write the half equation to represent the discharge. What will you observe at the electrode? Name the product. State the test to identify the product. Chemistry Perfect Score Module Form Set 3 44

4 Potassium chloride solution, 0.5 mol dm -3 Carbon electrodes Electrolysis of potassium chloride solution 9. Describe the electrolysis of potassium chloride solution using carbon electrodes. Anode Cathode Write the formula of all ions present in the electrolyte. Write the formula of ion/ions which is/are attracted to anode and cathode. Which is selectively discharged? Give a reason. Write the half equation to represent the discharge. What will you observe at the electrode? Name the product. Chemistry Perfect Score Module Form Set 3 45

5 Copper electrode Copper(II)nitrate solution, 0.5 mol dm -3 Iron electrode Electrolysis of copper (II) nitrate solution 10. Describe the electrolysis of copper (II) nitrate solution using metal electrodes. Anode Cathode Write the formula of all ions present in the electrolyte. Write the formula of ion/ions which is/are attracted to anode and cathode. Which is selectively discharged? Give a reason. Write the half equation to represent the discharge. What will you observe at the electrodes? Name the product. What will you observe to the electrolyte? Explain why? Chemistry Perfect Score Module Form Set 3 46

6 Voltaic cell / Simple cell Zinc electrode Copper(II)sulphate solution, 0.5 mol dm -3 Copper electrode 11. Describe the voltage cell. Negative terminal Positive terminal State all ions present in the electrolyte. Identify positive terminal and negative terminal. Explain why? Write half equation at negative terminal. Write the formula of ions which are moved to positive terminal. Which is selectively discharged? Give a reason. Half equation at positive terminal What will you observe at negative and positive terminal? What will you observe to the electrolyte? Explain why? Overall / Full ionic equation Chemistry Perfect Score Module Form Set 3 47

7 Application of electrolysis 12. State the aim of electroplating of metal The principal of electroplating. (a) The thing to be electroplating must be... (b) The electrolyte.... (c) The anode To electroplate the spoon with silver. Iron spoon Silver electrode Silver nitrate solution, 0.5 mol dm -3 (a) (b) (c) Write the half equation at silver electrode. Write the half equation at iron spoon. State the observation at silver electrode. (d) (e) State the observation at the iron spoon. An even and lasting layer of metal is obtained if: Chemistry Perfect Score Module Form Set 3 48

8 15. Purification of metal. (a) Things to be purified must be at... (b) The other electrode... (c) The electrolyte.. The electrochemical series 16. The electrochemical series 17. The electrochemical series can be constructed based on; (a) The potential difference between two metals, in voltaic cell. The higher the voltage value, the (b) The ability/ tendency of a metal to displace another metal from its salt solution. A metal which able to displace metal below it in the series from its salt solution. PAPER 2: STRUCTURE 1. Diagram 1 show the apparatus set-up used to electrolyze 0.1 mol dm -3 of sodium chloride solution using carbon electrodes. Gas P Gas Q 0.1 mol dm -3 of sodium chloride solution Electrode X _ + Electrode Y Diagram 1 (a) Name electrodes X and Y..... Chemistry Perfect Score Module Form Set 3 49

9 (b) Write the formula of all ions present in the solution.... (c) (i) Name gas P collected in the test tube. (ii) State a chemical test to confirm your answer to (c)(i). (iii) Write a half equation for the reaction that takes place at electrode X.... (d) (i) Name gas Q collected in the test tube.... (ii) State a chemical test to confirm your answer to (d)(i). (iii) Write a half equation for the reaction that takes place at electrode Y. (e) What difference will it make if the experiment is repeated by using 2 mol dm -3 of sodium chloride solution? Explain your answer. [2 marks] 2. Diagram 2 shows the apparatus set-up to carry out an electrolysis of aqueous copper(ii) sulphate solution. carbon electrdes Experiment I 0.2 mol dm -3 of copper(ii) sulphate solution Diagram 2 Experiment II copper elecrodes (a) Write the formula of all the ions present in the copper(ii) sulphate solution. Chemistry Perfect Score Module Form Set 3 50

10 (b) (i) Name the product produced at the anode in Experiment I. (ii) Write a half equation for the reaction that takes place at this electrode. (c) (i) Name the product produced at the anode in Experiment II. (ii) Write a half equation for the reaction that takes place at this electrode. (d) (i) What happen to the intensity of the blue copper(ii) sulphate solution in Experiment I? (ii) Explain your answer in (d) (i). (e) (i) What happen to the intensity of the blue copper(ii) sulphate solution in Experiment II? (ii) Explain your answer in (e) (i). 3. Diagram 3 shows a simple cell V electrode X electrode Y electrolyte Diagram 3 Chemistry Perfect Score Module Form Set 3 51

11 Two different electrodes are immersed into an electrolyte. The voltage of the cell is recorded. The experiment is repeated by using different pairs of electrode. Table 3 shows the results obtained. The metals of which electrodes V, W, X, Y and Z are made of, for divalent ions. Experiment Pairs of electrodes Positive terminal Negative terminal Voltage/V 1 X / Y Y X X / Z X Z X / W X W Y / V V Y 0.50 Table 3 (a) Suggest a suitable electrolyte for the above experiments.... (b) State the direction of the flow of electrons in Experiment 1 which used electrodes X and Y. (c) (d) (e).... Write half equation for the reaction that takes place at the negative terminal in Experiment 2 which used electrodes X and Z..... State a hypothesis for the above experiments. Arrange the metals V, W, X, Y and Z in decreasing order in the Electrochemistry Series..... (f) A chemical cell is set-up using electrodes Z and V. (i) State the negative terminal of the cell.... (ii) Calculate the voltage of the cell. (g) (i) State the pair of electrodes that will give the highest voltage reading. (ii) Calculate the voltage of the cell. Chemistry Perfect Score Module Form Set 3 52

12 PAPER 2 : ESSAY 4. (a) Ethanoic acid solution is electrolysed by using platinum electrode. What is produced at the cathode? Write a half equation for the reaction that occurs at the cathode. (b) Diagram 4 shows Cell X and Cell Y. [2 marks] V Zinc plate Copper plate copper electrode Cell X copper(ii) nitrate Diagram 4 Cell Y Cell X is a chemical cell while cell Y is an electrolytic cell. Compare cell X and cell Y. [8 marks] (c) A student wants to purify an impure copper plate by the process of electrolysis. Design an experiment in the laboratory to purify the impure copper plate. Your answer should include the following: materials and apparatus needed a diagram with the arrangement of apparatus the procedure observation chemical equation involved [10 marks] PAPER 3 : STRUCTURE 5. A student carries out an experiment to study the potential difference between two types of different metals. The apparatus arrangement used is shown in Diagram 5. Before experiment V After experiment V zinc plate Zinc plate iron plate copper(ii) nitrate iron plate Diagram 5 Chemistry Perfect Score Module Form Set 3 53

13 (a) State the observation and inference involved in the experiment in the table below. Metal plate Observation Inference Zinc Iron (b) The student repeated the experiment by replacing the iron metal with copper metal, aluminium metal and magnesium metal. Table 5 shows the voltage reading obtained from the metal pairs. Metal pairs Negative terminal Positive terminal Voltage/V Zinc iron Zinc Iron 0.4 Zinc copper Zinc Copper 1.1 Zinc almunium Aluminium Zinc 0.8 Zinc magnesium Magnesium Zinc 1.4 Table 5 Based on the information above, complete the table below. Type of variables (i) Manipulated variables : (ii) Responding variables : (iii) Constant variables : Action to be taken (i) Way to change the manipulated variables : (ii) How do these variables respond: (iii) Way to fix the constant variables : [6 marks] (c) State the hypothesis of the experiment (d) If the experiment is repeated by using lead metal to replace iron metal, predict the possible reading recorded by the voltmeter. Chemistry Perfect Score Module Form Set 3 54

14 6. Diagram 6 shows two set-up apparatus used to electrolyzed mol dm -3 hydrochloric acid and 1.0 mol dm -3 hydrochloric acid by using carbon electrodes. Carbon electrode mol dm -3 hydrochloric acid 1.0 mol dm -3 hydrochloric acid Diagram 6 (a) State a suitable hypothesis for the experiment. (b) State all the variables involved in the experiment (i) Manipulated variable (ii) Responding variable (iii) Constant variables (c) Write the observations at the anode and cathode for both sets of experiment. Terminal Electrolyte Set 1 ( mol dm -3 hydrochloric acid ) Set 2 ( 1.0 mol dm -3 hydrochloric acid ) Anode Cathode (d) Write half-equation for the discharge of ions at anode for Set 1 and Set Chemistry Perfect Score Module Form Set 3 55

15 (e) Predict the observation at the anode and cathode when mol dm -3 potassium nitrate solution is electrolysed. PAPER 3 : ESSAY 7. Concentration of ions used during electrolysis affects the product of electrolysis at the anode. Using sodium chloride solution, describe an experiment to prove the above statement. Your answer should include: (a) (b) (c) (d) (e) (f) Problem statement Hypothesis Variables Materials and apparatus used Procedure of the experiment Tabulation of data The further the distance between two metals in the electrochemical series, the bigger the potential difference. 8. You are given the copper strip, lead strip, iron strip, zinc strip, aluminium strip, magnesium strip and copper(ii) sulphate solution.referring to the statement above, plan a laboratory experiment to construct the electrochemical series of the potential differences using different pair of metals. Your explanation should include all the followings: (a) Aim of the experment (b) All the variables (c ) Statement of the hypothesis (d) List of materials and apparatus (e) Procedure of the experiment (f) Tabulation of data [ 17 marks ] Chemistry Perfect Score Module Form Set 3 56