Voltaic Cells 2018.notebook

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May 25, 2018

Apr 255:02 PM

Voltaic Cells a.k.a. Electrochemical cells

Aim: To analyze the process of a spontaneous chemical reaction that produces electricity.

Apr 410:14 AM

What is a Voltaic Cell?

Voltaic cell: an electrochemical cell where chemical energy is spontaneously converted to electrical energy.

The voltage produced by an electrochemical cell is measured in volts.

This is called the cell potential.

Apr 410:14 AM

• Two half‐cells with salt solutions • Wire and voltmeter• Anode and cathode electrodes • Salt bridge

Voltaic Cell

Parts of a Voltaic Cell

Apr 410:14 AM

Analyzing a Voltaic Cell• Use Table J to determine which metal is the site of oxidation.

• The MORE active metal oxidizes and will be the anode, the site of oxidation.

• The anode must be the negative electrode and the cathode must be the positive electrode.

• The cathode must attract e‐ lost at the anode and get them to move through the wire so reduction can occur.

Voltaic Cells 2018.notebook

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May 25, 2018

Apr 410:14 AM

Voltaic Cell

oxidation half reaction: reduction half

reaction:

WHY?  WHY? 

Apr 410:14 AM

Voltaic Cell

oxidation half reaction: reduction half

reaction:

WHY?  WHY? As Zn (s) metal oxidizes to form Zn+2 (aq) ions, the Zn+2 (aq) ions dissolve into solution.

As Cu2+ (aq) metal cations leave the solution they reduce into Cu (s) and stick onto the Cu cathode.

Salt Bridge Purpose: the salt bridge permits the flow of ions between the half cells to reduce the build up of excess charge.

Zn ‐‐> Zn+2 + 2e‐ Cu+2 + 2e‐ ‐‐> Cu

Cu+2 + Zn ‐‐> Cu + Zn+2

excess positive charge builds up as Zn+2 ions increase

excess negative charge builds up as Cu+2 ions decrease

Sep 212:51 PM

Copper ( Cu0)

Zinc ( Zn0)

Cl 

Zn0

Cu2+

Zn0

Cl 

Cl 

Zn0

Zn2+Cl 

Cl 

Zn2+

Zn0

Zn0

Zn0

Zn0

Zn0

Zn2+

Cu2+

Cu2+

Cu2+Cu2+

Cu0

Cu2+

Cu2+

1) Using Table J, determine which electrode is the anode and which is the cathode. Indicate the direction the electrons flow (current).

a. Anode:b. Cathode:c. Direction of electron flow:

2) What occurs at the anode? 

3) What happens to the electrons lost by the zinc electrode during oxidation?

4) Write the half reaction that occurs at the anode.

5) What happens to the mass of the anode? (hint: "OIL RIG")

Sep 212:51 PM

Copper ( Cu0)

Zinc ( Zn0)

Cl 

CuCl2(aq)ZnCl2(aq)

Zn0

Cu2+

Zn0

Cl 

Cl Zn0

Zn2+Cl 

Cl 

Zn2+

Zn0

Zn0

Zn0

Zn0

Zn0

Zn2+

Cu2+

Cu2+

Cu2+

Cu2+

Cu0

Cu2+

Cu2+

6) What occurs at the cathode? 

7) What is reduced at the cathode? 

8) Write the half reaction that occurs at the cathode.

9) What happens to the mass of the cathode?

10) How does the concentration of the Cu+2 ions change? How does the concentration of the Zn+2 ions change?

Cu0

Cu0

Cu0Zn0Zn0

Zn2+Zn2+

Zn0

Zn0 Zn0

Voltaic Cells 2018.notebook

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May 25, 2018

Apr 410:14 AM

How does a Voltaic Cell 

work?

• The wire connects the electrodes and the salt bridge connects the ionic solutions to complete the circuit.  The salt bridge promotes the flow of anions to prevent the buildup of charge in either half‐cell.

• Oxidation occurs at the ANODE and as electrons are lost, metal cations form and dissolve into the solution, decreasing the anodes mass through corrosion.

• The lost electrons from the metal of the anode attract to the positively charged cathode and flow through the wire.

• The electrons entering the metal cathode allow reduction at the CATHODE. Cations in the solution of the cathode half‐cell are reduced and they plate onto the cathode electrode, increasing the cathode’s mass.

• The flow of electrons and ions through the completed circuit generates electricity from the chemical reaction. VOLTAIC CELLS ARE SPONTANEOUS.

Apr 115:02 PM

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/galvan5.swf

Breaking Bad Galvanic Cell

VIDEOS

https://ny.pbslearningmedia.org/resource/rr11.chem.per.atomod.youstart/youstartattheanode/#.WwVY2ZeQwdU

https://www.youtube.com/watch?v=c320kqgXoLM#action=share

Apr 410:14 AM

Voltaic Cell

Apr 255:34 PM

Voltaic Cell Animations

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/galvan5.swf

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/galvan5.swfhttps://www.youtube.com/watch?v=gLZXC0ZFd08https://ny.pbslearningmedia.org/resource/rr11.chem.per.atomod.youstart/you-start-at-the-anode/#.WwVY2ZeQwdUhttps://www.youtube.com/watch?v=c320kqgXoLM#action=sharehttps://www.youtube.com/watch?v=J1ljxodF9_ghttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/galvan5.swf

Voltaic Cells 2018.notebook

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May 25, 2018

Apr 265:27 PM

Example 1: Mg Na

NaCl(aq)MgCl2(aq)

Write the oxidation and reduction half reactions for the cell. 

ox 1/2:

red 1/2:

2) What happens to the mass of both electrodes?Mg(s) mass ___________Na(s) mass ___________

3) What happens to the concentration of each of the following ions?Mg2+ concentration______________Na1+ concentration ______________

4) Which way do the electrons flow?

Apr 265:27 PM

Example 2:Write the oxidation and reduction half reactions for the cell. 

ox 1/2:

red 1/2:

2) What happens to the mass of both electrodes?Fe(s) mass ___________K (s) mass ___________

3) What happens to the concentration of each of the following ions?Fe+3 concentration______________K+1 concentration ______________

4) Which way do the electrons flow?

Fe K

FeCl3 (aq) KCl (aq)

May 239:11 AM

Cell #1 Cell #2 Cell #3

May 229:50 AM

Cell #1

Voltaic Cells 2018.notebook

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May 25, 2018

May 239:11 AM May 239:12 AM

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