Electrochemistry

Table of Reduction Potentials Measured against the Standard Hydrogen Electrode

Measuring Standard Electrode Potential Potentials are measured against a hydrogen ion reduction reaction, which is arbitrarily assigned a potential of zero volts.

Galvanic (Electrochemical) Cells Spontaneous redox processes have: A positive cell potential, E 0 A negative free energy change, (-  G)

Zn - Cu Galvanic Cell Zn e -  Zn E = -0.76V Cu e -  Cu E = +0.34V From a table of reduction potentials:

Zn - Cu Galvanic Cell Cu e -  Cu E = +0.34V The less positive, or more negative reduction potential becomes the oxidation… Zn  Zn e - E = +0.76V Zn + Cu 2+  Zn 2+ + Cu E 0 = V

Line Notation Zn(s) | Zn 2+ (aq) || Cu 2+ (aq) | Cu(s) An abbreviated representation of an electrochemical cell Anodesolution Anodematerial Cathodesolution Cathodematerial ||||

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Electrolytic Processes A negative cell potential, (-E 0 ) A positive free energy change, (+  G) Electrolytic processes are NOT spontaneous. They have:

Electroplating of Silver Anode reaction: Ag  Ag + + e - Electroplating requirements: 1. Solution of the plating metal 3. Cathode with the object to be plated 2. Anode made of the plating metal 4. Source of current Cathode reaction: Ag + + e -  Ag

Solving an Electroplating Problem Q: How many seconds will it take to plate out 5.0 grams of silver from a solution of AgNO 3 using a 20.0 Ampere current? 5.0 g Ag + + e -  Ag 1 mol Ag g 1 mol e - 1 mol Ag C 1 mol e - 1 s 20.0 C = 2.2 x 10 2 s

Read 17.1 – 17.2 –#13-34 (17.3 – 17.6 Informational) Read 17.7 –#63-67 –#73-79