Voltaic Cells
voltaic cell: a device that uses a
spontaneous redox reaction to
create an electric current
Batteries are voltaic cells
A voltaic cell contains two electrodes and an
electrolyte
electrode: solid conductors
electrolyte: aqueous conductors
cathode: positive electrode
anode: negative electrode
Voltaic Cell Design
A voltaic cell can be built from two half-cells
Each half-cell contains an electrode and an
electrolyte
Simplest half-cell is a solid metal dipped in a
metal ion solution
The two half-cells are connected by:
1) a wire connecting the two electrodes (may
be run through a voltmeter)
2) a porous boundary (salt bridge or ceramic
cup) connecting the two electrolytes
General design of a voltaic cell:
The SOA is always reduced in the
cathode half-cell.
The SRA is always oxidized in the
anode half-cell.
The Daniell Cell
Made up of copper and zinc half-cells
The Daniell cell
Cu2+(aq) is the SOA in the system and will
most easily gain e−
Zn(s) are the SRA in the system and will
most easily lose e−
Cathode: Cu2+(aq) + 2e- → Cu(s)
Anode:
Zn(s) → Zn2+(aq) + 2e-
Net Cell Reaction:
Cu2+(aq) + Zn(s) → Cu(s) + Zn2+(aq)
Electrons travel through wire from
anode(−) to cathode(+)
In the salt bridge, anions flow
towards the anode and cations flow
towards the cathode
As the cell operates:
1)The Cu(s) will increase in mass
2)The Zn(s) will decrease in mass
3)The blue color of the Cu2+(aq) will
fade away