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C/W

Electrolysis. 04/02/14. C/W. Starter: 1. Have your periodic tables out ready 2. On your whiteboard write down any properties of ionic compounds that you remember HINT: high or low boiling point? Conducts electricity? Soluble?. LO: Define electrolysis

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C/W

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  1. Electrolysis 04/02/14 C/W Starter: 1. Have your periodic tables out ready 2. On your whiteboard write down any properties of ionic compounds that you rememberHINT: high or low boiling point? Conducts electricity? Soluble? LO: Define electrolysis Recognise substances that can undergo electrolysis Predict the products of electrolysis

  2. Is sodium chloride ionic or covalent? • How do you know? • Metal + non-metal  ionic compound • Draw a sodium atom and a chlorine atom • Show how they bond (HINT: you need an arrow) • Draw the ions that are formed

  3. Electrolysis Electrolysis uses an electric current to break down an ionic substance into its elements http://www.youtube.com/watch?v=TyNUqX5lb-0&safe=active

  4. Predict the products of electrolysis of… • Iron chloride • Lead iodide • Aluminium oxide • Zinc bromide • Copper chloride

  5. We are going to carry out electrolysis of copper chloride? • What will we make? • What will we see at the electrodes? • We are not going to do this with molten copper chloride – can you think why not?

  6. WEAR GOGGLES • Connect up the circuit as shown in the diagram (on the powerpack use 4V and DC) • Turn on the circuit and record your observations. You may smell chlorine at one electrode. • Use litmus paper to test the gas – chlorine turns litmus white • As soon as you have made observations turn the power off – CHLORINE IS TOXIC Carbon electrodes Power supply (4V) Copper chloride solution (electrolyte)

  7. Peer assess • Bubbling / gas produced (1), colour change / chlorine smell (1) • Red solid forming on electrode (1) • Chlorine gas (1) turned litmus paper white (1) • Copper (1) • Positively charged copper ions move to negative electrode (1), negatively charged chloride ions move to positive electrode (1) • Copper chloride has a high melting point (1) too high to melt in a school lab (1) • In molten or dissolved copper chloride the ions are free to move (1) but in a solid they cannot move (1) • Copper chloride  copper + chlorine (1) • CuCl2 (aq)  Cu (s) + Cl2 (g) (1 for correct formulae, 1 for correct state symbols)

  8. Changes at electrodes 05/02/14 C/W Starter: Ready for a quiz on last lesson’s work? LO: 1. Describe what happens to ions during electrolysis 2. Predict products of electrolysis

  9. Molten NaCl - What happens at the electrodes? • Cl- ion moves to positively charged electrode loses an electron to form a Cl atom – 2 Cl atoms bond to make a molecule of chlorine gas this is oxidation • Na+ ion moves to negatively charged electrode gains an electron to form Na atom This is reduction • OILRIG - Oxidation Is Loss (of electrons), Reduction Is Gain

  10. For electrolysis of each molten compound, answer the following questions • What forms at the positive electrode? • What forms at the negative electrode? • Describe what happens at each electrode. Use the words ion, electron, oxidised, reduced, atom. A – lithium fluoride B – lead bromide (careful – how many electrons are needed?) C – copper chlorideIons: Li+ F- Pb2+ Br- Cu2+Cl-

  11. A - At the positive electrode fluoride ion loses an electron and forms fluorine atom. This is oxidation. 2 fluorine atoms bond together to form fluorine gas.At the negative electrode a lithium ion gains an electron and forms a lithium atom. This is reduction. B – lead bromide (careful – how many electrons are needed?) At the positive electrode a bromide ion loses an electron loses an electron and forms a bromine atom. This is oxidation. At the negative electrode a lead ions gains two electrons and forms a lead atom. This is reduction. C – copper chloride At the positive electrode a chloride ion loses an electron and forms a chlorine atom. This is oxidation. At the negative electrode copper ions gain two electrons and form copper atoms. This is reduction.

  12. Half equations Eg Lead chloride Pb2+ + 2e- Pb 2Cl-  Cl2 + 2e- Write half equations for A, B and C

  13. When electrolysis occurs in aqueous solutions, the changes at the electrode are more complex • Water contains H+ and OH- ions

  14. When electrolysis occurs in aqueous solutions, the changes at the electrode are more complex • Water contains H+ and OH- ions • Sometimes H+ ions move to the negatively charged electrode and form hydrogen H2 gas • Sometimes OH- ions move to the positively charged electrode and form oxygen O2 gas • RULE: the less reactive element will be produced

  15. RULE: the less reactive element will be produced

  16. Predict what will be produced during electrolysis of: • Molten copper bromide • Copper bromide solution • Iron sulfate solution • Potassium chloride solution • Molten sodium chloride • Solid calcium sulfate Answer Qs in text book page 155

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