Lecture30 - Chem 162, Lecture 30, Spring 2011 Zinc is added...

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Chem 162, Lecture 30, Spring 2011 Zinc is added to a solution of copper (II) sulfate. Z n ( s ) + C u 2+ (aq) Zn 2+ (aq) + Cu(s) Half reactions: Anode Zn(s) Zn 2+ (aq) + 2e - Cathode Cu 2+ (aq) + 2e - Cu(s) A galvanic cell can be constructed from these two half reactions. Zinc is anode Copper is cathode
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In order to conveniently tabulate voltages, we make a chart in which each half reaction is measured against a standard reference electrode, chosen to be the standard hydrogen electrode (SHE). The standard hydrogen electrode consists of a solution containing 1.0 M H + ions (such as 1.0 M HCl) in contact with 1.0 atm of H 2 (g). A platinum electrode serves as the location, where electrons get transferred. If electrons come into the hydrogen electrode, reducing H + to H 2 , it is the cathode. 2 H + + 2e - H 2 (g) E o = 0.00 volts cathode reaction Or, if electrons leave the hydrogen electrode, oxidizing H 2 to H + ions, it is the anode H 2 (g) 2H + + 2e - E o = 0.00 volts anode reaction The direction of electron flow depends on the other half reaction. No matter whether the SHE serves as the cathode or the anode, it is assigned a standard reduction(oxidation) potential of E o = 0.00 volts Consider the case of a standard Cu/Cu 2+ electrode set up with the standard hydrogen electrode. Cu is the cathode Pt is the anode Cell notation: Pt(s)|H 2 (g, 1atm)| H + (aq, 1 M)||Cu 2+ (aq, 1 M)|Cu(s) The voltmeter shows = 0.34 V.
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Electrons flow from the Pt electrode to the Cu electrode. The half reactions are: A n o d e : H 2 2H + + 2e - Cathode: Cu 2+ + 2e - Cu(s) Overall: H 2 + Cu 2+ Cu(s) + 2H + In our table, we write all reactions as reductions. As the reference electrode, we assign 0.00 volts to the reaction: 2 H + + 2e - H 2 E o = 0.00 volts Then: E o cell = 0.34 V = E o cathode - E o anode = E o Cu 2+ /Cu – E o H + /H 2 = E o Cu 2+ /Cu – 0.0 V => E o Cu 2+ /Cu = 0.34 V Since Pt is the anode and Cu is the cathode, Cu 2+
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This note was uploaded on 11/09/2011 for the course CHEM 162 taught by Professor Siegal during the Spring '08 term at Rutgers.

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Lecture30 - Chem 162, Lecture 30, Spring 2011 Zinc is added...

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