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Dry Cell Battery Anode (-) Zn ---> Zn 2+ + 2e- Cathode (+) 2 NH 4 + + 2e- ---> 2 NH 3 + H 2 Common dry cell Copyright © 1999 by Harcourt Brace & Company All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida
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2 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Nearly same reactions as in common dry cell, but under basic conditions. Alkaline Battery
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3 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Anode: Zn is reducing agent under basic conditions Cathode: HgO + H 2 O + 2e- ---> Hg + 2 OH - Mercury Battery
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4 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Lead Storage Battery Anode (-) E o = +0.36 V Pb + HSO 4 - ---> PbSO 4 + H + + 2e- Cathode (+) E o = +1.68 V PbO 2 + HSO 4 - + 3 H + + 2e- ---> PbSO 4 + 2 H 2 O
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5 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Ni-Cad Battery Anode (-) Cd + 2 OH - ---> Cd(OH) 2 + 2e- Cathode (+) NiO(OH) + H 2 O + e- ---> Ni(OH) 2 + OH -
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Electrolysis of Aqueous NaOH Anode (+) E o = -0.40 V 4 OH - ---> O 2 (g) + 2 H 2 O + 2e- Cathode (-) E o = -0.83 V 4 H 2 O + 4e- ---> 2 H 2 + 4 OH - E o for cell = -1.23 V Electric Energy ----> Chemical Change Copyright © 1999 by Harcourt Brace & Company All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida
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7 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Electrolysis Electric Energy ---> Chemical Change Electrolysis of molten NaCl. Here a battery “pumps” electrons from Cl - to Na +.
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8 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Electrolysis of Molten NaCl Anode (+) E o = -1.36 V 2 Cl - ---> Cl 2 (g) + 2e- Cathode (-) E o = -2.71 V Na + + e- ---> Na E o for cell = -4.07 V External energy needed because E o is (-). Note that signs of electrodes are reversed from batteries.
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9 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Electrolysis of Aqueous NaCl Anode (+) E o = -1.36 V 2 Cl - ---> Cl 2 (g) + 2e- Cathode (-) E o = -0.83 V 2 H 2 O + 2e- ---> H 2 + 2 OH - E o for cell = -2.19 V Note that H 2 O is more easily reduced than Na +.
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10 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Electrolysis of Aqueous NaCl Cells like these are the source of NaOH and Cl 2. In 1995 25.1 x 10 9 lb Cl 2 25.1 x 10 9 lb Cl 2 26.1 x 10 9 lb NaOH 26.1 x 10 9 lb NaOH Also the source of NaOCl for use in bleach.
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11 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Electrolysis of Aqueous CuCl 2 Anode (+) E o = -1.36 V 2 Cl - ---> Cl 2 (g) + 2e- Cathode (-) E o = +0.34 V Cu 2+ + 2e- ---> Cu E o for cell = -1.02 V Note that Cu is more easily reduced than either H 2 O or Na +.
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12 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Producing Aluminum 2 Al 2 O 3 + 3 C ---> 4 Al + 3 CO 2 Charles Hall (1863-1914) developed electrolysis process. Founded Alcoa.
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Quantitative Aspects of Electrochemistry Consider electrolysis of aqueous silver ion. Ag + (aq) + e- ---> Ag(s) 1 mol e----> 1 mol Ag If we could measure the moles of e-, we could know the quantity of Ag formed. But how to measure moles of e-? Copyright © 1999 by Harcourt Brace & Company All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida
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14 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry Consider electrolysis of aqueous silver ion. Ag + (aq) + e- ---> Ag(s) 1 mol e----> 1 mol Ag If we could measure the moles of e-, we could know the quantity of Ag formed. But how to measure moles of e-?
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15 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry Consider electrolysis of aqueous silver ion. Ag + (aq) + e- ---> Ag(s) 1 mol e----> 1 mol Ag If we could measure the moles of e-, we could know the quantity of Ag formed. But how to measure moles of e-?
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16 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved But how is charge related to moles of electrons? Charge on 1 mol of e- = (1.60 x 10 -19 C/e-)(6.02 x 10 23 e-/mol) = 96,500 C/mol e- = 1 Faraday Quantitative Aspects of Electrochemistry
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17 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry 1.50 amps flow thru a Ag + (aq) solution for 15.0 min. What mass of Ag metal is deposited? Solution (a)Calc. charge Coulombs = amps x time = (1.5 amps)(15.0 min)(60 s/min) = 1350 C
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18 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry 1.50 amps flow thru a Ag + (aq) solution for 15.0 min. What mass of Ag metal is deposited? Solution (a)Charge = 1350 C (b)Calculate moles of e- used
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19 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry 1.50 amps flow thru a Ag + (aq) solution for 15.0 min. What mass of Ag metal is deposited? Solution (a)Charge = 1350 C (b)Calculate moles of e- used
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20 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry 1.50 amps flow thru a Ag + (aq) solution for 15.0 min. What mass of Ag metal is deposited? Solution (a)Charge = 1350 C (b)Calculate moles of e- used (c)Calc. quantity of Ag
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21 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry 1.50 amps flow thru a Ag + (aq) solution for 15.0 min. What mass of Ag metal is deposited? Solution (a)Charge = 1350 C (b)Calculate moles of e- used (c)Calc. quantity of Ag
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22 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry The anode reaction in a lead storage battery is Pb(s) + HSO 4 - (aq) ---> PbSO 4 (s) + H + (aq) + 2e- If a battery delivers 1.50 amp, and you have 454 g of Pb, how long will the battery last? Solution a)454 g Pb = 2.19 mol Pb b)Calculate moles of e-
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23 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry The anode reaction in a lead storage battery is Pb(s) + HSO 4 - (aq) ---> PbSO 4 (s) + H + (aq) + 2e- If a battery delivers 1.50 amp, and you have 454 g of Pb, how long will the battery last? Solution a)454 g Pb = 2.19 mol Pb b)Calculate moles of e-
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24 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry The anode reaction in a lead storage battery is Pb(s) + HSO 4 - (aq) ---> PbSO 4 (s) + H + (aq) + 2e- If a battery delivers 1.50 amp, and you have 454 g of Pb, how long will the battery last? Solution a)454 g Pb = 2.19 mol Pb b)Calculate moles of e- c)Calculate charge
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25 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry The anode reaction in a lead storage battery is Pb(s) + HSO 4 - (aq) ---> PbSO 4 (s) + H + (aq) + 2e- If a battery delivers 1.50 amp, and you have 454 g of Pb, how long will the battery last? Solution a)454 g Pb = 2.19 mol Pb b)Calculate moles of e- c)Calculate charge 4.38 mol e- 96,500 C/mol e- = 423,000 C 4.38 mol e- 96,500 C/mol e- = 423,000 C
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26 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry The anode reaction in a lead storage battery is Pb(s) + HSO 4 - (aq) ---> PbSO 4 (s) + H + (aq) + 2e- If a battery delivers 1.50 amp, and you have 454 g of Pb, how long will the battery last? Solution a)454 g Pb = 2.19 mol Pb b)Mol of e- = 4.38 mol c)Charge = 423,000 C
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27 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry The anode reaction in a lead storage battery is Pb(s) + HSO 4 - (aq) ---> PbSO 4 (s) + H + (aq) + 2e- If a battery delivers 1.50 amp, and you have 454 g of Pb, how long will the battery last? Solution a)454 g Pb = 2.19 mol Pb b)Mol of e- = 4.38 mol c)Charge = 423,000 C d)Calculate time
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28 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry The anode reaction in a lead storage battery is Pb(s) + HSO 4 - (aq) ---> PbSO 4 (s) + H + (aq) + 2e- If a battery delivers 1.50 amp, and you have 454 g of Pb, how long will the battery last? Solution a)454 g Pb = 2.19 mol Pb b)Mol of e- = 4.38 mol c)Charge = 423,000 C d)Calculate time
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29 Copyright (c) 1999 by Harcourt Brace & Company All rights reserved Quantitative Aspects of Electrochemistry The anode reaction in a lead storage battery is Pb(s) + HSO 4 - (aq) ---> PbSO 4 (s) + H + (aq) + 2e- If a battery delivers 1.50 amp, and you have 454 g of Pb, how long will the battery last? Solution a)454 g Pb = 2.19 mol Pb b)Mol of e- = 4.38 mol c)Charge = 423,000 C d)Calculate time About 78 hours
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