Topic: Redox

Aim: What are electrochemical cells?

Do Now: Which of the following ions is most easily reduced?

1) Li+ 2) K+ 3) Ca2+ 4) Na+

HW:

Types of Cells

Electrochemical Cells

• Practical uses for redox reactions

• Involve:– Chemical rxns– Flow of e-

• 2 types:– Voltaic (galvanic)– Electrolytic

Voltaic Cell

• produce electricity as a result of chemical rxns

• These rxns are spontaneous

• These rxns cause the flow of e-. Therefore, electricity is produced.

• Parts of a voltaic cell (drawn on board)

Voltaic Cell

Parts of Voltaic Cell

1. Two Half Cells:- Each half of the redox reaction takes place in a

separate container.- The 2 containers (2 half cells) are connected by a

SALT BRIDGE.- Allows ions to move, but does not allow the solutions

to mix!2. Electrodes

a. Anode – where oxidation occurs (LEO) An Oxb. Cathode – where reduction occurs (GER) Red Cat

Parts, cont.

3.Salt Bridge

4.Switch

5.Wire

6.Voltmeter

7.Solutions in Both Half Cells

Voltaic Cell Info

• ANODE is NEGATIVE• CATHODE is POSITIVE• (Think: they are in alphabetical order!)• Electrons flow from anode to cathode b/c

opposites attract (e- are negative, cathode is positive)– Also, anode is oxidation – loss of e-, cathode is

reduction – gain of e-

• This spontaneous flow produces electricity.

Voltaic Cell Info

• When given a voltaic cell, how do you know which metal electrode is the anode and which is the cathode?

• The metal HIGHER ON TABLE J will be the ANODE and LOSE ELECTRONS b/c it is MORE EASILY OXIDIZED than the other metal (below it)!

Review Questions

• In the reaction:Zn Zn2+ + 2e-

Is Zn oxidized or reduced?

• In the reaction:Zn + Cu2+ Zn2+ + CuWhich is reduced, Cu2+, Cu, Zn2+, or Zn?

• Which one has a stronger tendency to lose electrons when they are in contact with an electrolyte, Cu2+, Cu, Zn2+, or Zn?

Review Questions

• What is responsible for the conduction of electricity in the solution?

• The salt-bridge is the path for what to move?

Examples of Voltaic Cells

• Batteries– a dry cell battery is what you find in your typical

electronic device.– The reason you often need more than one battery is

because a single battery doesn’t provide enough volts of power. When connected in a series (end to end), the voltage is multiplied.

Electrolytic Cells

• produce chemical reactions as a result of electric current

• These rxns are non-spontaneous

• These rxns use the flow of e-. Therefore, electricity is used.

• Parts of an electrolytic cell (drawn on board)

Electrolytic Cell

Parts of Electrolytic Cell

1. One Cell:- Both halves of the redox reaction take place in the

same container.2. Electrodes

a. Anode – where oxidation occurs (LEO) An Oxb. Cathode – where reduction occurs (GER) Red Cat

Parts, cont.

3. Wire

4. Battery/power source

5. Solution in Cell

Electrolytic Cell Info

• ANODE is POSITIVE• CATHODE is NEGATIVE• Electrons still flow from anode to cathode b/c

opposites attract (e- are negative, cathode is positive)– Also, anode is oxidation – loss of e-, cathode is

reduction – gain of e-

Electroplating