Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary In a battery the electricity comes from: A chemical reaction. A flow of electrons Electricity passing along wires is:

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary Batteries run out When the chemicals in them are used up. Some batteries can be recharged. Like the lead/acid car battery Or The nickel/cadmium battery

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary An electrolyte is A liquid that conducts electricity. Batteries contain the electrolyte ammonium chloride. Because it completes the circuit.

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary Electricity can be produced by battery or mains Mains electricity is :- Cheaper Electricity from batteries is: Safer – lower voltages More portable Both types use energy from fossil fuels Batteries produce waste that damages the environment

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary A cell producing electricity can be made when 2 different metals are connected together with an electrolyte.

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary Electrochemical Series By connecting different pairs of metals we can produce an When set up in a cell: A metal high in the series will send electrons to a lower metal. 2 metals far apart in the series give a high voltage 2 metals close in the series give a low voltage.

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary Here is part of the Electrochemical Series. The complete series is in the Data Book

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary PotassiumP CalciumC SodiumS MagnesiumM AluminiumA ZincZ IronI NickelN TinT LeadL HydrogenH CopperCu Silver Ag MercuryHg GoldAu

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary Redox Reactions A REDOX reaction involves the 2 processes of Oxidation and Reduction. REDOX reactions involve a transfer of electrons. OOxidation IIs LLoss of electrons RReduction IIs GGain of Electrons

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary Electrons flow through the wires from the higher metal to the lower metal. (Mg to Pb) Cell Reactions Pb 2+ ions (lead ions) move to the lead electrode Mg  Mg e - Magnesium dissolves forming magnesium ions Pb e - -> Pb

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary Mg  Mg e - Pb e - -> Pb The ion bridge is there to complete the circuit. The ion bridge allows ions to flow between the 2 solutions. The magnesium dissolves away gradually and the lead gets heavier as more lead ions turn into lead.

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary Get Out copper! Displacement Reactions A metal can displace a lower metal from a solution of its compound. Magnesium displaces copper from copper sulphate solution The products are magnesium sulphate and copper. Mg (s) + CuSO 4 (aq) -> MgSO 4 (aq) + Cu(s) The more reactive magnesium has pushed copper out of its compound and taken its place. OUT!

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary Ion-electron equations These show the oxidation and reduction steps in a REDOX reaction. The copper ions in copper sulphate are turning into copper metal. Mg (s) + CuSO 4 (aq) -> MgSO 4 (aq) + Cu(s) Magnesium is dissolving to form magnesium ions: Mg (s)  Mg 2+ (aq) + 2e - Cu 2+ (aq) + 2e -  Cu(s) Loss of electrons Oxidation Gain of electrons Reduction

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary Electrolysis and ion-electron equations Electrolysis is the breakdown of an ionic compound using electricity. Non-metals are discharged at the positive electrode. Metals (and hydrogen) are discharged at the negative electrode.

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary Electrolysis of Copper (II) Chloride Copper ions go to the negative electrode and form copper Cu 2+ (aq) + 2e -  Cu(s) Chloride ions go to the positive electrode and form chlorine. 2Cl - (aq)  Cl 2 (g) + 2e - Loss of electrons - Oxidation Gain of electrons - Reduction

Topic 10 - Making Electricity B Gilday – St Thomas Aquinas Secondary A Cell Without Metals Carbon electrode Solution of iodide ions Solution of iron (III) ions Ion bridge Electron flow Since electron flow is from left to right, iodide must lose electrons: 2I - (aq)  I 2 + 2e - Loss of electrons - Oxidation Iron (III) ions must gain electrons: Fe 3+ (aq) + e -  Fe 2+ (aq) Gain of electrons - Reduction