1. I am learning to understand redox reactions EXAM TIPS: You may be asked to apply your understanding to industrial processes such as hair removal, plating metals etcYou may be asked to apply your understanding to industrial processes such as hair removal, plating metals etc

2. I am learning to understand redox reactions Outcomes: I will demonstrate I understand at Grade C by Recall the products of the electrolysis of brine. List some uses of the products of the electrolysis of brine Outcomes: I will demonstrate I understand at Grade A by Explain how brine can be electrolysed. Generate half equations for the electrolysis of brine. Objectives: I will understand That brine can be electrolysed. The uses of the products of the electrolysis of brine.

3. I am learning to understand redox reactions WHAT’S BRINE?

4. I am learning to understand redox reactions OILRIGOILRIG Write down which electrode the ions may move to, then look at reactivity

5. I am learning to understand redox reactions

6. Use the diagram on p188 and annotate!

7. I am learning to understand redox reactions In the electrolysis of NaCl solution, the negative chloride ions (Cl - ) are attracted to the positive electrode (anode). 2Cl -  Cl 2 + 2e - (oxidation) Here, the Cl - ions lose electrons to make chlorine atoms, which then form chlorine molecules (Cl 2 ). Chlorine Are the Cl - ions oxidized or reduced? How many electrons are lost by each Cl - ion? How many Cl - ions join to make a Cl 2 molecule? What is the half-equation for this redox process? oxidized one two

8. I am learning to understand redox reactions In the electrolysis of sodium chloride solution, the Na + ions might be expected to form sodium at the negative electrode (cathode). For all ionic compounds containing a metal that is more reactive than hydrogen, electrolysis will produce hydrogen rather than the metal. At the negative electrode, both the H + ions and the Na + ions are attracted. However, the Na + H + ions so the H + ions gain electrons; and the Na + ions stay in solution. At the negative electrode, both the H + ions and the Na + ions are attracted. However, the Na + are more stable than the H + ions so the H + ions gain electrons; and the Na + ions stay in solution. Instead, hydrogen gas is produced here Instead, hydrogen gas is produced here. This is because sodium chloride solution also contains H + ions from the water: H 2 O (l)  H + (aq) + OH - (aq). Why isn’t Sodium formed?

9. I am learning to understand redox reactions Complete the table for these compounds increasing reactivity potassium sodium calcium magnesium aluminium zinc iron copper gold lead silver (carbon) (hydrogen) platinum If an ionic compound contains a metal that is more reactive than hydrogen, electrolysis of a solution of the compound will produce hydrogen, not the metal. hydrogen copper hydrogen silver hydrogen potassium chloride copper sulphate sodium bromide silver nitrate zinc chloride Ionic compound Product at the negative electrode

10. I am learning to understand redox reactions The electrolysis of sodium chloride solution produces three very useful products: Chlorine used for killing bacteria in water, for bleach and making plastics like PVC. Hydrogen used for making margarine and fertilizers, and for rocket fuel. Sodium hydroxide used in many chemical reactions, such as making soap, neutralizing acids and making paper. Products of the Electrolysis of NaCl

11. I am learning to understand redox reactions Which of the 3 products would be used for… MargarineMargarine PVCPVC BleachBleach SoapSoap PaperPaper Rayon fibresRayon fibres DetergentsDetergents Purification of aluminium orePurification of aluminium ore Hydrochloric acid manufactureHydrochloric acid manufacture

12. I am learning to understand redox reactions Outcomes: I will demonstrate I understand at Grade C by Recall the products of the electrolysis of brine. List some uses of the products of the electrolysis of brine Outcomes: I will demonstrate I understand at Grade A by Explain how brine can be electrolysed. Generate half equations for the electrolysis of brine. Objectives: I will understand That brine can be electrolysed. The uses of the products of the electrolysis of brine.

13. I am learning to understand redox reactions Electrolysis of dilute sulfuric acid Which product will form at each electrode? The conductivity of water can be improved by adding dilute sulfuric acid. This releases more ions so that more current flows during electrolysis, which creates hydrogen and oxygen. Water can be electrolysed to give hydrogen (for fuel cells) and oxygen. Water is covalent and so is a poor conductor of electricity. There are a few free H + & OH - ions: H 2 O (l)  H + (aq) + OH - (aq). Oxygen gas at Anode (+), Hydrogen at cathode (-)

14. I am learning to understand redox reactions

15. Electrolysis of sulphuric acid What is the overall equation for the electrolysis of dilute sulfuric acid? At the negative (cathode) electrode: 2H + + 2e -  H 2 (reduction) 2H 2 O (l)  2H 2 (g) + O 2 (g) Twice as much hydrogen forms as oxygen. In water, there are 2 hydrogen atoms for every oxygen atom, so the ratio by volume, of H 2 to O 2, is 2:1. At the positive (anode) electrode: 4OH -  2H 2 O + O 2 + 4e - (oxidation)

16. I am learning to understand redox reactions Summary notes Brine is a solution of sodium chloride in water. When it is electrolysed, hydrogen is produced at the negative electrode from hydrogen ions in the water. Chlorine is produced at the positive electrode from the chloride ions. This leaves sodium ions and hydroxide ions (from water) in the solution. The half equations for the reactions at the electrodes are: At the positive electrode:2Cl - Cl 2 +2e - At the negative electrode:2H + +2e - H 2 Sodium hydroxide is a strong alkali and has many uses including making soap, making paper, making bleach, neutralising acids and controlling pH. Chlorine is used to kill bacteria in drinking water and swimming pools, and to make bleach, disinfectants and plastics. Hydrogen is used to make margarine and hydrochloric acid. You may be asked to apply your knowledge of electrolysis to other industrial processes.

17. I am learning to understand redox reactions Check your understanding 1.What are the four ions present in brine? 2.Explain why sodium hydroxide is left in the solution? 3.Give two uses for each of the products. ANSWERS: 1.Sodium Na +, hydrogen H +, chloride Cl -, hydroxide OH - 2.Hydrogen ions and chloride ions are discharged, leaving sodium ions and hydroxide ions in the solution. 3.Hydrogen: making margarine, making hydrochloric acid Chlorine: sterilising water, making bleach, making disinfectants, making plastics Sodium hydroxide: making paper, soap, bleach, to control pH CLICK AGAIN FOR THE ANSWERS

18. I am learning to understand redox reactions Extra Notes

19. I am learning to understand redox reactions