Applications of Voltaic Cellsfc.gsacrd.ab.ca/~cblair/FOV2-0006C414/FOV2-0006CC02/ch13 L4-applications.pdfApplications of Voltaic Cells Lesson 4 chapter 13 Objective You will be able

Applications of Voltaic CellsLesson 4

chapter 13

ObjectiveYou will be able to explain how the development of the voltaic cell had affected society.

Dry CellsSince voltaic cells are not portable, dry cells were developed.

These cells have an electrolyte that is thickened into a paste, but can still allow electrons to move.

Dry cells are batteries

example

Cathode Reaction

MnO2(s) + H2O(l) + 2 e- ➔ Mn2O3(s) + 2 OH-(aq)

Anode Reaction

Zn(s) ➔ Zn2+ + 2 e-

Button Battery

Dry cells stop producing electrical energy when the reactants are used upA battery is a set of voltaic cells connected in series

Example: a 9 volt battery is really six 1.5 volt dry cells connected in series(In a series connection, the negative electrode of one cell is connected to the positive electrode of another cell)

Features of a Dry Cell

A primary cell is one that cannot be recharged. A secondary cell can be rechargedElectrical energy is used to reverse the reaction in the cell and replenish the reactants

We will focus on primary cells.

Lead acid car battery: secondary cell

Cathode is lead (IV) oxide

Reaction:

Anode is lead

Reaction:

Cathode is lead (IV) oxide

Reaction?

Anode is lead

Reaction?

When your car is running, an electric current, produced by the alternator, reverses the cathode and anode reactions.This replenishes the reactants so the battery does not go “dead”

When your car is running, an electric current, produced by the alternator, reverses the cathode and anode reactions.

This replenishes the reactants so the battery does not go “dead”

A battery that can be refueledThey are designed so the reactants flow into the cell, and the products flow outFuel cells are more efficient than combustion engines or generators and do not produce greenhouse gases or other polluting gases

Fuel Cells

Net Reaction2 H2(g) + O2(g) ➔ 2 H2O(l)

What is the cell potential for the hydrogen fuel cell?

Cathode: O2(g) + 4 H+ + 4 e- ➔2 H2O

Anode: H2(g) ➔ 2 H+ + 2 e-

The fuel cell provides a highly efficient conversion of the chemical energy in hydrogen, natural gas, or hydrocarbons into electrical energy, and because of their high energy density (energy per unit weight of the power source), fuel cells are superior to batteries in portable equipment.

CorrosionCorrosion is a spontaneous redox reaction of a metal with substances in the environment

Metals can be oxidized by the oxygen in our atmosphereRust is produced when iron is oxidized to form

Fe2O3 • x H2OThe surface of a piece of iron acts like a voltaic cell

AnodeIron

CathodeInert material (usually impurity in the iron)

Cathode: O2 + 2 H2O + 4 e- ➔4 OH-

Anode: Fe ➔Fe2+ + 2 e-

Net: 2 Fe + O2 + 2 H2O ➔ 2 Fe(OH)2(s)The Fe(OH)2(s) further reacts to form

Fe2O3 • x H2O

PreventionPaint or enamel coatings prevent air and water from reaching the metal.

GalvanizingCovering iron with zincZinc is more reactive than iron (SRA) so it will be oxidized instead of iron, making a coating that protects the iron.

Cathodic ProtectionAttaching a more reactive metal to an iron object (Al, Mg, Zn)The more reactive metal is oxidized instead of the iron (sometimes called a sacrificial anode)Must be periodically replaced as they are used up

An advantage of sacrificial anode systems is the flexibility in application. Anodes can be installed in a variety of applications and configurations. No outside power is required for cathodic protection to be effective. Another advantage is the minimal maintenance required for these systems to function.

AssignmentRead text p.491-501Do review questions #1-5,8,13,14.