What process occurs at the cathode? Write an equation for the reaction?
Objectives of the first lesson: teach how to write diagrams for the electrolysis of solutions and molten salts and apply the acquired knowledge to solve calculation problems; continue to develop skills in working with the textbook and test materials; discuss the use of electrolysis in the national economy. FIRST LESSON PLAN 1. Repetition of studied methods for obtaining metals. 2. Explanation of new material. 3. Solving problems from the textbook by G.E. Rudzitis, F.G. Feldman “Chemistry-9” (M.: Prosveshchenie, 2002), p. 120, no. 1, 2. 4. Testing knowledge acquisition on test tasks. 5. Report on the use of electrolysis. Objectives of the first lesson: teach how to write diagrams for the electrolysis of solutions and molten salts and apply the acquired knowledge to solve calculation problems; continue to develop skills in working with the textbook and test materials; discuss the use of electrolysis in the national economy. PROGRESS OF THE FIRST LESSON Repetition of learned methods obtaining metals using the example of copper production from copper(II) oxide. Writing the equations of the corresponding reactions: 
Another way to obtain metals from solutions and melts of their salts is electrochemical, or electrolysis. Electrolysis is a redox process that occurs at the electrodes when an electric current is passed through a melt or electrolyte solution. Electrolysis of sodium chloride melt: cathode (–) (Na+): Na++ е =Na0, anode (–) (Cl – ): Cl – – е = Cl 0 , 2Cl 0 = Cl2; Electrolysis of sodium chloride solution: cathode (–) (Na + ; H + ): H + + е = H 0 , 2H 0 = H2 anode (+) (Cl – ; OН – ): Cl – – е = Cl 0 , 2Cl 0 = Cl2; Electrolysis of copper(II) nitrate solution: cathode (–) (Cu 2+ ; H + ): Cu 2+ + 2е = Cu 0 , anode (+) (OH –): OH – – е =OH 0, These three examples show why electrolysis is more profitable than other methods of producing metals: metals, hydroxides, acids, and gases are obtained. We wrote electrolysis diagrams, and now let’s try to write electrolysis equations right away, without referring to the diagrams, but only using the ion activity scale: 
Examples of electrolysis equations: Problem solving from the textbook by G.E. Rudzitis and F.G. Feldman (9th grade, p. 120, No. 1, 2). Task 1. During electrolysis of a solution of copper(II) chloride, the mass of the cathode increased by 8 g. What gas was released, what is its mass? (Cu) = 8/64 = 0,125 mol, m(Cl2) = 0,125•71 = 8,875 g. Response. Gas – chlorine weighing 8,875 g. Task 2. During electrolysis of an aqueous solution of silver nitrate, 5,6 liters of gas were released. How many grams of metal are deposited on the cathode? (Ag) = 4(O2) = 4•25 = 1 mol, m(Ag) = 1•107 = 107 g. Response. 107 g silver. The test is Option 1 1. During electrolysis of a solution of potassium hydroxide at the cathode, the following is released: a) hydrogen; b) oxygen; c) potassium. 2. During the electrolysis of a solution of copper(II) sulfate in solution, the following is formed: a) copper(II) hydroxide; b) sulfuric acid; 3. During electrolysis of a barium chloride solution at the anode, the following is released: a) hydrogen; b) chlorine; c) oxygen. 4. During the electrolysis of molten aluminum chloride at the cathode, the following is released: a) aluminum; b) chlorine; c) electrolysis is impossible. 5. Electrolysis of a silver nitrate solution proceeds according to the following scheme: Option 2 1. During electrolysis of a sodium hydroxide solution at the anode, the following is released: a) sodium; b) oxygen; c) hydrogen. 2. During the electrolysis of a solution of sodium sulfide in solution, the following is formed: a) hydrosulfide acid; b) sodium hydroxide; 3. During the electrolysis of a melt of mercury(II) chloride at the cathode, the following is released: a) mercury; b) chlorine; c) electrolysis is impossible. 4. During electrolysis of a silver nitrate solution at the cathode, the following is released: a) silver; b) hydrogen; c) oxygen. 5. Electrolysis of a solution of mercury(II) nitrate proceeds according to the following scheme: Option 3 1. During electrolysis of a solution of copper(II) nitrate at the cathode, the following is released: a) copper; b) oxygen; c) hydrogen. 2. During the electrolysis of a solution of lithium bromide in solution, the following is formed: b) hydrobromic acid; c) lithium hydroxide. 3. During the electrolysis of molten silver chloride at the cathode, the following is released: a) silver; b) chlorine; c) electrolysis is impossible. 4. During the electrolysis of an aluminum chloride solution, aluminum is released into: a) cathode; b) anode; c) remains in solution. 5. Electrolysis of a barium bromide solution proceeds according to the following scheme: Option 4 1. During the electrolysis of a barium hydroxide solution at the anode, the following is released: a) hydrogen; b) oxygen; c) barium. 2. During the electrolysis of a solution of potassium iodide in solution, the following is formed: a) hydroiodic acid; b) water; c) potassium hydroxide. 3. During the electrolysis of molten lead(II) chloride at the cathode, the following is released: a) lead; b) chlorine; c) electrolysis is impossible. 4. During electrolysis of a silver nitrate solution at the cathode, the following is released: a) silver; b) hydrogen; c) oxygen. 5. Electrolysis of a sodium sulfide solution proceeds according to the following scheme: Replies
| Option | Question 1 | Question 2 | Question 3 | Question 4 | Question 5 |
| 1 | а | б | б | а | б |
| 2 | б | б | а | а | б |
| 3 | а | в | а | в | а |
| 4 | б | в | а | а | а |
Application of electrolysis in the national economy 1. To protect metal products from corrosion, a thin layer of another metal is applied to their surface: chromium, silver, gold, nickel, etc. Sometimes, in order not to waste expensive metals, a multilayer coating is produced. For example, the exterior parts of a car are first coated with a thin layer of copper, a thin layer of nickel is applied to the copper, and a layer of chrome is applied to it. When coatings are applied to metal by electrolysis, they are even in thickness and durable. In this way, you can coat products of any shape. This branch of applied electrochemistry is called electroplating. 2. In addition to protecting against corrosion, galvanic coatings give a beautiful decorative appearance to products. 3. Another branch of electrochemistry, similar in principle to electroplating, is called galvanoplasty. It is the process of making exact replicas of various items. To do this, the object is coated with wax and a matrix is obtained. All recesses of the copied object on the matrix will be bulges. The surface of the wax matrix is coated with a thin layer of graphite, making it conductive to electrical current. The resulting graphite electrode is immersed in a bath of copper sulfate solution. Copper serves as the anode. During electrolysis, the copper anode dissolves and copper is deposited on the graphite cathode. This way an exact copper copy is obtained. Electroplating is used to make printing clichés, gramophone records, and metallize various objects. Galvanoplasty was discovered by the Russian scientist B.S. Jacobi (1838). Making record stamps involves applying a thin silver coating to a plastic record to make it electrically conductive. An electrolytic nickel coating is then applied to the plate. What should the plate in the electrolytic bath be made of – anode or cathode? (O t v e t. Cathode.) 4. Electrolysis is used to produce many metals: alkali, alkaline earth, aluminum, lanthanides, etc. 5. To purify some metals from impurities, the metal with impurities is connected to the anode. The metal dissolves during electrolysis and is released at the metal cathode, while the impurity remains in solution. 6. Electrolysis is widely used for the production of complex substances (alkalis, oxygen-containing acids) and halogens.
Water electrolysis circuit
Practical work
(second lesson) Lesson objectives. Conduct electrolysis of water, demonstrate galvanostegy in practice, and consolidate the knowledge acquired in the first lesson. Equipment. On students’ desks: flat battery, two wires with terminals, two graphite electrodes, a beaker, test tubes, a stand with two legs, a 3% sodium sulfate solution, an alcohol lamp, matches, a torch. On the teacher’s desk: the same + solution of copper sulfate, brass key, copper tube (piece of copper). Instructing students 1. Attach the wires with terminals to the electrodes. 2. Place the electrodes in a glass so that they do not touch. 3. Pour electrolyte solution (sodium sulfate) into a glass. 4. Pour water into the test tubes and, lowering them upside down into a glass with electrolyte, put them on the graphite electrodes one by one, securing the upper edge of the test tube in the tripod leg. 5. After the device is mounted, attach the ends of the wires to the battery. 6. Observe the release of gas bubbles: less of them are released at the anode than at the cathode. After almost all the water in one test tube is replaced by the released gas, and in the other – half, disconnect the wires from the battery. 7. Light the alcohol lamp, carefully remove the test tube, where the water has almost completely been displaced, and bring it to the alcohol lamp – a characteristic pop of gas will be heard. 8. Light a torch. Remove the second test tube and check the gas with a smoldering torch. Student assignments 1. Sketch the device. 2. Write an equation for the electrolysis of water and explain why it was necessary to carry out electrolysis in a solution of sodium sulfate. 3. Write reaction equations reflecting the release of gases at the electrodes. Teacher demonstration experiment
(can be performed by the best students in the class
if appropriate equipment is available) 1. Connect the wire terminals to the copper tube and brass wrench. 2. Place the tube and key into a glass with a solution of copper(II) sulfate. 3. Connect the other ends of the wires to the battery: “minus” of the battery to the copper tube, “plus” to the key! 4. Observe the release of copper on the surface of the key. 5. After completing the experiment, first disconnect the terminals from the battery, then remove the key from the solution. 6. Disassemble the electrolysis circuit with a soluble electrode: CuSO4 = Cu 2+ + anode (+): Cu 0 – 2e = Cu 2+ , cathode (–): Cu 2+ + 2e = Cu 0 . The overall equation for electrolysis with a soluble anode cannot be written. Electrolysis was carried out in a solution of copper(II) sulfate because: a) an electrolyte solution is needed for electric current to flow, because water is a weak electrolyte; b) no reaction by-products will be released, but only copper at the cathode.
A 9th grade student spends
practical work
“Electrolysis of water”
7. To consolidate what has been learned, write a diagram of the electrolysis of zinc chloride with carbon electrodes: cathode (–): Zn 2+ + 2e = Zn 0 , anode (+): 2Cl – – 2e =Cl2. The overall reaction equation cannot be written in this case, because it is unknown what part of the total amount of electricity goes to the restoration of water, and what part goes to the reduction of zinc ions.
Scheme of the demonstration experiment
Homework 1. Write an equation for the electrolysis of a solution containing a mixture of copper(II) nitrate and silver nitrate with inert electrodes. 2. Write the equation for the electrolysis of sodium hydroxide solution. 3. To clean a copper coin, it must be suspended on a copper wire connected to the negative pole of the battery and immersed in a 2,5% NaOH solution, where a graphite electrode connected to the positive pole of the battery should also be immersed. Explain how the coin becomes clean. (Response. The reduction of hydrogen ions occurs at the cathode: Hydrogen reacts with copper oxide located on the surface of the coin: This method is better than cleaning with powder, because. the coin is not erased.) Inspiring routes, unusual recipes, reviews of devices, sports news, make-up tutorials, analysis of scientific theories, recommendations for choosing a car, reviews of exhibitions – in Zen you can write texts and shoot videos on any topic! And smart algorithms will always help you find an audience that will be interested. Join the Zen writing community and unleash your creative potential to the fullest. Create a channel 
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