ElectrochemistElectrochemistryry

Table of Table of Reduction Reduction PotentialsPotentials

Measured Measured against against

the the StandardStandardHydrogenHydrogenElectrodeElectrode

Measuring Measuring Standard Standard Electrode Electrode PotentialPotential

Potentials are measured against a Potentials are measured against a hydrogen ion reduction reaction, which hydrogen ion reduction reaction, which is arbitrarily assigned a potential of is arbitrarily assigned a potential of zero zero voltsvolts..

Galvanic (Electrochemical) Galvanic (Electrochemical) CellsCells

Spontaneous redox processes

have:A positive cell potential, E0

A negative free energy change, (-G)

Zn - Cu Zn - Cu Galvanic Galvanic

CellCell

Zn2+ + 2e- Zn E = -0.76V

Cu2+ + 2e- Cu E = +0.34V

From a From a table of table of reduction reduction potentials:potentials:

Zn - Cu Zn - Cu Galvanic Galvanic

CellCell

Cu2+ + 2e- Cu E = +0.34V

The less positive, The less positive, or more negative or more negative reduction reduction potential potential becomes the becomes the oxidation…oxidation…

Zn Zn2+ + 2e- E = +0.76V

Zn + Cu2+ Zn2+ + Cu E0 = + 1.10 V

Line Line NotationNotation

Zn(Zn(ss) | Zn) | Zn2+2+((aqaq) || Cu) || Cu2+2+((aqaq) | Cu() | Cu(ss))

An abbreviated An abbreviated representation representation of an of an electrochemical electrochemical cellcell

AnodeAnodesolutionsolution

AnodeAnodematerialmaterial

CathodeCathodesolutionsolution

CathodeCathodematerialmaterial|| ||||||

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ElectrolytElectrolytic ic

ProcesseProcessess

A negative cell potential, (-E0)

A positive free energy change, (+G)

Electrolytic processes are NOT spontaneous. They have:

Electroplating Electroplating of Silverof Silver

Anode reactionAnode reaction::

Ag Ag Ag Ag++ + e + e--

Electroplating requirementsElectroplating requirements::1. Solution of the plating metal1. Solution of the plating metal

3. Cathode with the object to be plated3. Cathode with the object to be plated2. Anode made of the plating metal2. Anode made of the plating metal

4. Source of current4. Source of current

Cathode reactionCathode reaction::

AgAg++ + e + e-- Ag Ag

Solving an Electroplating Solving an Electroplating ProblemProblem

Q: How many seconds will it take to Q: How many seconds will it take to plate out 5.0 grams of silver from a plate out 5.0 grams of silver from a solution of AgNOsolution of AgNO33 using a 20.0 Ampere using a 20.0 Ampere current?current?

5.0 g

AgAg++ + e + e- - Ag Ag

1 mol Ag

107.87 g

1 mol e-

1 mol Ag

96 500 C

1 mol e-

1 s

20.0 C

= 2.2 x 10= 2.2 x 1022 s s

• Read 17.1 – 17.2 – #13-34

• (17.3 – 17.6 Informational)• Read 17.7

– #63-67– #73-79