Voltaic+cell

A **//voltaic cell//** is a device used to obtain electrical energy from a redox chemical reaction.

The oxidation reaction and the reduction reaction are carried out separately each in a separate electrochemical half cell. Each half cell consists of a metal dipped in a solution of its own ions.
 * // For example a zinc-copper voltaic cell: //**

At the //zinc half cell// the zinc atom oxidises to zinc ions: Zn Zn 2+  (aq) + 2e - At the //copper half cell//, there is an equilibrium between copper metal and copper ions: Cu (s) Cu 2+  (aq) + 2e - Zinc is higher than copper in the reactivity series and thus it is a good reducing agent. Thus if the two half cell are connected together by a wire, electrons will flow through it from the zinc half cell to the copper half cell. 

As //zinc// is giving up **electrons** , it forms the //negative electrode//.

As //copper// is ** receiving electrons **, it forms the //positive electrode//.

To avoid a build up of charges, the ions should also be able to flow from one solution to another. This is done by the use of a salt bridge (usually a filter paper, dipped in a strong solution of an electrolyte)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">* **Oxidation** occurs at the **negative electrode** and thus this is known as the //anode//

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">* **Reduction** occurs at the **positive electrode** and thus this is known as the //cathode//

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The overall reaction that occurs is:

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Zn (s) + Cu 2+ <span style="font-family: Tahoma,sans-serif; font-size: 14pt;"> (aq) ---> Zn 2+ <span style="font-family: Tahoma,sans-serif; font-size: 14pt;"> (aq) + Cu (s)

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">In the figure, positive ions are being produced on the left and consumed on the right. Thus, through the salt bridge, positive ions flow from left to right and negative ions flow from right to left.

// The more reactive metal will always be the negative electrode. //

// The greater the difference in the reactivity of the metals, the greater the cell potential. //

By the end of this lesson you should be able to: media type="googleplusone" key="" width="360" height="18" media type="facebooklike" key="http%3A%2F%2Fibchem4u.wikispaces.com%2FVoltaic%20cell" width="360" height="74" **<span style="color: #800080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">NEXT UP- ELECTROLYTIC CELLS **
 * Explain how a redox reaction is used to produce electricity in a voltaic cell
 * State that oxidation occurs at the negative electrode (anode) and reduction occurs at the positive electrode (cathode)