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17.1 Explain how a non-spontaneous redox reaction can be driven forward during electrolysis 17.1 Relate the movement of charge through an electrolytic cell to the chemical reactions that occur 17.1 Apply the principle of electrolysis to its applications such as chemical synthesis, refining, plating, and cleaning.
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17.2 Relate the construction of a galvanic cell to how it functions to produce a voltage and an electrical current 17.2 Trace the movement of electrons in a galvanic cell 17.2 Relate chemistry in a redox reaction to separate reactions occurring at electrodes in a galvanic cell
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Oxidation reduction reactions involve a transfer of electrons. OIL- RIG Oxidation Involves Gain Reduction Involves Loss LEO-GER Lose Electrons Oxidation Gain Electrons Reduction
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Galvanic Cells (Voltaic) = A battery which uses spontaneous chemical processes to produce electricity ◦ The amount of electricity depends on how bad the atoms (molecules) want the electrons or want to give them up.
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Corrosion: The oxidation of metals over time from being oxidized by surrounding oxidizing agents (such as oxygen). ◦ Generally very slow, but some are more quickly oxidized (depending on activity of metal as a solid)
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How to stop corrosion: Sacrificial Anodes. Since some metals corrode easier than others, we have the metal we want safe (steel, iron) in contact with a metal that is more easily oxidized (like zinc). ◦ The zinc gets oxidized first, and loses electrons and takes the hit instead of the iron or steel.
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Running a reaction backwards ◦ Forcing electrons onto the atoms/molecules Separating Atoms ◦ Give everyone an octet without each other Used to separate metals from their salts
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Using electrolysis to place aqueous metals onto a surface. ◦ This is how jewelry is plated in gold and silver, how silver ware is coated in silver, but not completely out of silver ware.
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Moving electrons is electric current. 8H + +MnO 4 - + 5Fe +2 +5e - Mn +2 + 5Fe +3 +4H 2 O Helps to break the reactions into half reactions. 8H + +MnO 4 - +5e - Mn +2 +4H 2 O 5(Fe +2 Fe +3 + e - ) In the same mixture it happens without doing useful work, but if separate
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H + MnO 4 - Fe +2 Connected this way the reaction starts Stops immediately because charge builds up.
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Reducin g Agent Oxidizin g Agent e-e- e-e- e-e- e-e- e-e- e-e- AnodeCathode
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Oxidizing agent pushes the electron. Reducing agent pulls the electron. Unit is the volt(V)
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Zn +2 SO 4 -2 1 M HCl Anode 0.76 1 M ZnSO 4 H + Cl - H 2 in Cathod e
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1 M HCl H + Cl - H 2 in This is the reference all other oxidations are compared to E º = 0 º indicates standard states of 25ºC, 1 atm, 1 M solutions.
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Zn(s) + Cu +2 (aq) Zn +2 (aq) + Cu(s) The total cell potential is the sum of the potential at each electrode. E º cell = E º Zn Zn +2 + E º Cu +2 Cu We can look up reduction potentials in a table. One of the reactions must be reversed, so change the sign.
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Determine the cell potential for a galvanic cell based on the redox reaction. Cu(s) + Fe +3 (aq) Cu +2 (aq) + Fe +2 (aq) Fe +3 (aq) + e - Fe +2 (aq) E º = 0.77 V Cu +2 (aq)+2e - Cu(s) E º = 0.34 V Cu(s) Cu +2 (aq)+2e - E º = -0.34 V 2Fe +3 (aq) + 2e - 2Fe +2 (aq) E º = 0.77 V
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solid Aqueous Aqueous solid Anode on the left Cathode on the right Single line different phases. Double line porous disk or salt bridge. For the last reaction Cu(s) Cu +2 (aq) Fe +2 (aq),Fe +3 (aq)
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Rusting - spontaneous oxidation. Most structural metals have reduction potentials that are less positive than O 2. ◦ If you are more positive on the chart, you can oxidize anything below you (the product)
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Water Rust Iron Dissolves- Fe Fe +2 e-e- Salt speeds up process by increasing conductivity
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Coating to keep out air and water. Galvanizing - Putting on a zinc coat Has a lower reduction potential, so it is more. easily oxidized. Alloying with metals that form oxide coats. Cathodic Protection - Attaching large pieces of an active metal like magnesium that get oxidized instead.
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1.0 M Zn +2 e-e- e-e- Anode Cathode 1.10 Zn Cu 1.0 M Cu +2
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Cathode (Reduction) Half-Reaction Standard Potential E ° (volts) Li + (aq) + e - Li(s) -3.04 K + (aq) + e - K(s) -2.92 Fe 2+ (aq) + 2e - Fe(s) -0.41 Pb 2+ (aq) + 2e - Pb(s) -0.13 Cu+(aq) + e- Cu(s) 0.52 I 2 (s) + 2e- 2I-(aq) 0.54 Ag + (aq) + 1e- Ag (s) 0.80 Pt +2 (aq) + 2e- Pt (s) 1.23 Cl 2 (g) + 2e- 2Cl- (aq) 1.36 1.Write the chemical shorthand for a Lead and Lithium battery. 2.What is the cell potential for a Iron and Platinum battery? 3.Which element (and charge) is the best oxidizing agent? 4.Which element (and charge) is the best reducing agent?
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