ElectrochemistryLesson 8

Electrochemical Cells

Electrochemical cells are Batteries

Alkaline Batteries

KOH

Car Batteries

Pb-Acid H2SO4

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Cell Phone batteries

Lithium Ion Rechargeable battery

Lithium Coin Cell

Space Ship Batteries

Powered by Radioisotopes

Ni-Metal Hydride

Notes on Electrochemical Cells 

An electrochemical cell – a system of electrodes, electrolytes, and salt bridge that allow oxidation and reduction reactions to occur and electrons to flow through an external circuit.

The salt bridge allows ions to migrate from one half-cell to the other without allowing the solutions to mix.

1. Spontaneous redox reaction       2. Produces electricity from chemicals

3. Is commonly called a battery

Analyzing Electrochemical Cells

The reaction that is higher on the reduction chart is the reduction and the lower is oxidation and is written in reverse.

For any cell Oxidation always occurs at the anode and reduction at the cathodeElectrons flow through the wire and go from anode to cathodeAnions (- ions) migrate to the anode and cations (+ions) migrate towards the cathode usually through the salt bridge

voltmeter

1. Draw and completely analyze a Cu/Sn electrochemical cell.

Higher

Greatest Electron Affinity

Reduction

Cathode

Cu2+ + 2e- → Cu(s)

0.34 v

Gains mass

+

CuSn

Cu2+

NO3-

Sn2+

NO3-Na-+

NO3-

0.48 v

Lower

Oxidation

Anode

Sn(s) → Sn2+ + 2e-

+0.14 v

Loses mass

-

Overall Reaction: Cu2+ + Sn → Sn2+ + Cu(s) 0.48 v

e-e-

The Hydrogen half cell involves a gas and requires an inert or nonreactive Pt electrode.

H2(g) in

Wire to circuit

Pt(s)

1 M HCl

H+

Cl-

1.0 M KNO3

0.80 v 0.80 v

AgH2

voltmeter 2e-

2e-

H+

Cl-

Ag+

NO3-

NO3

- K+

2Ag+ + H2 → 2Ag + 2H+ 0.80 v

Draw a H2/Ag electrochemical cell with a KNO3 salt bridge.

HigherGreater electron affinityReductionCathode+

Ag+ + 1e- → Ag(s)

+0.80 vGains mass

oxidationAnode-

H2 → 2H+ + 2e-

0.00 vpH decreases

1 M HCl 1 M AgNO3

Pt