iGCSE Chemistry Lesson 1 Electrolysis.pptx

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1. Do now: E lectrolysis Which type of compound can conduct an electric current? Why? Why can these substances conduct a current only when they’re dissolved in a solution?

2. Metals form cations, non-metals form anions Cations are positive, they have lost electrons Anions are negative, they have gained electrons

3. The process of electrolysis Ionic compounds conduct an electric current because they are made up of charged particles. These substances conduct a current only when they’re dissolved because the ions are able to move freely when in a solution.

4. The process of electrolysis Predict: Which ion would be attracted to each electrode*? Explain why. *An electrode is an electrical conductor used to make contact with a part of a circuit that is not metal.

5. The process of electrolysis OPPOSITES ATTRACT!

6. How to remember the Anode and Cathode Cat-ions are paws-itive And they live in the cat’s home (cathode)

7. Oxidation and reduction ANODE CATHODE

8. Half equations 2Cl - → Cl 2 + 2e -

9. The process of electrolysis OPPOSITES ATTRACT! During electrolysis, the ions become attracted to the electrodes because they have an electric charge : Electrode attracting the cations has a negative charge. Electrode attracting the anions has a positive charge. the cations are attracted to the “ Cathode ” The anions are attracted to the “ Anode ”

10. Process of electrolysis

11. Rules at the electrodes Cathode ○ hydrogen (from H + in water) is produced UNLESS the + ions in the ionic compound are from a metal less reactive than hydrogen ○ if the metal is less reactive, it will be produced instead Anode ○ oxygen (from OH - in water) will be produced UNLESS the ionic compound contains halide ions (Cl - , Br - , I - ) ○ if there are halide ions, the halogen will be produced instead (e.g. Cl 2 )

12. Predict the products Predict what the products would be of these ionic compounds at each electrode. Ionic compound Product at anode ( + ) Product at cathode (-) Sodium chloride (NaCl) Chlorine Sodium Copper (II) oxide (CuO) Oxygen Copper Potassium Iodide (KI) Calcium oxide (CaO) Lithium Fluoride LiF Magnesium oxide (MgO) Magnesium chloride (MgCl 2 ) Beryllium bromide ( Be Br 2 ) Sodium iodide (NaI) Calcium chloride (CaCl 2 )

13. Mark your work in green pen Ionic compound Product at anode (+ ) Product at cathode (-) Sodium chloride (NaCl) Chlorine Sodium Copper (II) oxide (CuO) Oxygen Copper Potassium Iodide (KI) Iodine Potassium Calcium oxide (CaO) Oxygen Calcium Lithium Fluoride Li F Fluorine Lithium Magnesium oxide (MgO) Oxygen Magnesium Magnesium chloride (MgCl 2 ) Chlorine Magnesium Beryllium bromide ( Be Br 2 ) Bromine Beryllium Sodium iodide (NaI) Iodine Sodium Calcium chloride (CaCl 2 ) Chlorine Calcium

14. Predict the products Ionic compound Product at anode (+) Product at cathode Sodium chloride (NaCl) Chlorine gas Sodium metal Copper (II) oxide (CuO) Oxygen gas Copper metal Potassium Iodide solution (KI) Calcium oxide (CaO) Lithium Fluoride solution LiF (aq) Magnesium oxide (MgO) Magnesium chloride (MgCl 2 ) Beryllium bromide (BeBr 2 ) Sodium iodide solution (NaI) Calcium chloride (CaCl 2 )

15. Mark your work in green pen Ionic compound Product at anode Product at cathode Sodium chloride (NaCl) Chlorine gas Sodium metal Copper (II) oxide (CuO) Oxygen gas Copper metal Potassium Iodide solution (KI) Iodine gas Hydrogen gas Calcium oxide (CaO) Oxygen gas Calcium metal Lithium Fluoride solution LiF (aq) Fluorine gas Hydrogen gas Magnesium oxide (MgO) Oxygen gas Magnesium metal Magnesium chloride (MgCl 2 ) Chlorine gas Magnesium metal Beryllium bromide (BeBr 2 ) Bromine gas Beryllium metal Sodium iodide solution (NaI) Iodine gas Hydrogen gas Calcium chloride (CaCl 2 ) Chlorine gas Calcium metal

16. Task - The process of electrolysis Draw the diagram and annotate for the electrolysis of copper sulfate (Cu Cl 2 ). Label your diagram: Cathode, anode, cation, anion, Cu 2+ , Cl - , oxidation, reduction, electrolyte (ionic solution). Explain what is happening at each electrode. Where is oxidation and reduction happening? Why? Why can this happen with ionic compounds in solution? Write half equations for what is happening at each electrode.

17. Mark your work The negative ion ( anion ) is attracted to the positive electrode ( anode ). The positive ion ( cation ) is attracted to the negative electrode ( cathode ). This can happen with ionic compounds when they are in solution (dissolved) because the ions can move. Cathode (negative electrode) Anode (positive electrode) Cation (positive ion) Cu 2+ Cl - Anion (negative ion) Electrolyte (solution) Oxidation is happening at the anode because it’s a loss of electrons. Reduction is happening at the cathode because it’s a gain of electrons.

18. Examples to learn ○ Molten lead (II) bromide ■ Pb 2+ to cathode, Pb (s) is produced (not in solution so these are the only + ions present) ■ Br - to anode, Br 2(l) is produced (not in solution so these are the only - ions present) ○ Concentrated hydrochloric acid ■ H + ions go to cathode, H 2(g) is produced (H + is present in both water and HCl) ■ Cl - ions go to anode, Cl 2(g) is produced (Cl - are halide ions) ○ Concentrated sodium chloride solution ■ H + ions go to cathode, H 2(g) is produced (Na is more reactive than hydrogen) ■ Cl - ions go to anode, Cl 2(g) is produced (Cl - are halide ions) ○ Dilute sulfuric acid ■ H + to cathode, H 2(g) is produced (these are the other ions present in sulfuric acid H 2 SO 4 ) ■ OH - to anode, O2 (g) is produced (SO 4 2- ions are not halide ions)

19. Manufacturing sodium hydroxide and chlorine Sodium hydroxide and chlorine are manufactured by the electrolysis of concentrated sodium chloride solution (brine) in a diaphragm cell. Diaphragm = a thin sheet of material forming a partition.

20. Exam question

21. Mark scheme

22. Purification of copper - electrolysis

23. Oxidation and reduction ANODE CATHODE

24. H alf equations 2Cl - → Cl 2 + 2e -

25. H alf equations

26. Write half equations for what would happen at each electrode Ionic compound Half eq at anode Half eq at cathode Sodium chloride (NaCl) 2Cl - (aq) → Cl 2(g) + 2e - Na + (aq) + e - → Na (s) Copper (II) oxide (CuO) Oxygen gas Copper metal Potassium Iodide solution (KI) Iodine gas Hydrogen gas Calcium oxide (CaO) Oxygen gas Calcium metal Lithium Fluoride solution LiF (aq) Fluorine gas Hydrogen gas Magnesium oxide (MgO) Oxygen gas Magnesium metal Magnesium chloride (MgCl 2 ) Chlorine gas Magnesium metal Beryllium bromide (BeBr 2 ) Bromine gas Beryllium metal Sodium iodide solution (NaI) Iodine gas Hydrogen gas Calcium chloride (CaCl 2 ) Chlorine gas Calcium metal

27. Check your work Ionic compound Half eq at anode Half eq at cathode Sodium chloride (NaCl) 2Cl - (aq) → Cl 2(g) + 2e - Na + (aq) + e - → Na (s) Copper (II) oxide (CuO) 2O 2- (aq) → O 2(g) + 4e - Cu 2+ (aq) + 2e - → Cu (s) Potassium Iodide solution (KI) 2I - (aq) → I 2(g) + 2e - 2H + (aq) + 2e - → H 2(g) Calcium oxide (CaO) 2O 2- (aq) → O 2(g) + 4e - Ca 2+ (aq) + 2e - → Ca (s) Lithium Fluoride solution LiF (aq) 2F - (aq) → F 2(g) + 2e - 2H + (aq) + 2e - → H 2(g) Magnesium oxide (MgO) 2O 2- (aq) → O 2(g) + 4e - Mg 2+ (aq) + 2e - → Mg (s) Magnesium chloride (MgCl 2 ) 2Cl - (aq) → Cl 2(g) + 2e - Mg 2+ (aq) + 2e - → Mg (s) Beryllium bromide (BeBr 2 ) 2Br - (aq) → Br 2(g) + 2e - Be 2+ (aq) + 2e - → Be (s) Sodium iodide solution (NaI) 2I - (aq) → I 2(g) + 2e - 2H + (aq) + 2e - → H 2(g) Calcium chloride (CaCl 2 ) 2Cl - (aq) → Cl 2(g) + 2e - Ca 2+ (aq) + 2e - → Ca (s)