Lecture 19sf

Lecture 19sf - Copper is added to a solution of silver...

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Copper is added to a solution of silver nitrate Cu(s) + 2Ag + (aq) → 2Ag(s) + Cu 2+ (aq) Cu(s) gets oxidized (gives off electrons) Ag + (aq) gets reduced (gains electrons) We can separate the overall reaction into two half reactions Half reactions: Oxidation: Cu(s) → Cu 2+ (aq) + 2e - Reduction: Ag + (aq) + e - → Ag(s) Adding these two half-reactions up, first multiplying the reduction reaction by 2 to cancel electrons, we get the overall reaction: Cu(s) + 2Ag + (aq) → 2Ag(s) + Cu 2+ (aq) A spontaneous oxidation-reduction reaction such as shown above can be designed as a voltaic cell – a way to generate a flow of electrons or electricity. Such a voltaic cell is commonly called a battery. A voltaic cell can be constructed by physical separation of the half reactions, with a salt bridge or porous barrier between the two sides to allow ion flow. Electricity flows through the external circuit only “on demand,” meaning when the circuit is connected. The two electrodes of the cell are called the anode and cathode. Anode: where oxidation occurs (electrons leave) Cathode: where reduction occurs (electrons enter) For the reaction described above: Anode: Cu(s) → Cu 2+ (aq) + 2e - Cathode: Ag + (aq) + e - → Ag(s)
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Cu is anode Ag is cathode We can also represent this diagram with a cell notation. Cu(s)|Cu 2+ (1M) || Ag + (1M)| Ag(s) In this notation the double line || separates the anode and cathode parts of the cell. By convention, the anode is written on the left side and the cathode on the right side. anode || cathode The single line | represents a phase boundary between different sections of the anode or cathode. Zinc is added to a solution of copper (II) sulfate. Zn(s) + Cu 2+ (aq) → Zn 2+ (aq) + Cu(s) Half reactions: Anode Zn(s) → Zn 2+ (aq) + 2e - Cathode Cu 2+ (aq) + 2e - → Cu(s) A voltaic cell can be constructed from these two half reactions.
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Zinc is anode Copper is cathode We can also represent this diagram with a cell notation. Zn(s)|Zn 2+ (1M) || Cu 2+ (1M)| Cu(s) Zinc is added to a solution of silver nitrate Zn(s) + 2Ag + (aq) → 2Ag(s) + Zn 2+ (aq) Half reactions: Anode Zn(s) → Zn 2+ (aq) + 2e - Cathode Ag + (aq) + e - → Ag(s) A voltaic cell can be constructed from these two half reactions.
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Zinc is anode Silver is cathode We can also represent this diagram with a cell notation. Zn(s)|Zn 2+ (1M) || Ag + (1M)| Ag(s) 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. 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
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Lecture 19sf - Copper is added to a solution of silver...

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