Experiment 10: The Voltaic Cell

• Voltaic cells or galvanic cells are devices in which the transfer of electrons takes place through an external pathway rather than directly between reactants present in the same reaction vessel.
• A salt bridge is a chamber of electrolytes necessary to complete the circuit in a voltaic cell (for the current to flow)
• The oxidation and reduction reactions are separated into compartments called half-cells.
• The anode is an electrode where oxidation occurs (left half-cell).
• The cathode is an electrode where reduction occurs (right half-cell).
• the electrode written to the left of the salt bridge in this cell notation is always taken to be the anode, the electrode to the right of the salt bridge is therefore always the cathode
• In a cell notation, a single vertical line indicates a phase boundary. The double vertical line represents a salt bridge.
• The potential difference between the two electrodes of a voltaic cell is called the cell potential, denoted Ecell. Because the potential difference provides the driving force that pushes electrons through the external circuit, we also call it the electromotive (“causing electron motion”) force, or emf. Always positive.
• The cell potential under standard conditions (1 atm ,1 M, and 25 C) is called either the standard cell potential or standard emf and is denoted E°cell.
• For each half-cell in a voltaic cell, the standard reduction potential provides a measure of the tendency for reduction to occur. The more positive the value of E°red, the greater the tendency for reduction under standard conditions. →A positive reduction potential tells us that it is easier to reduce (better oxidizing agent) →A negative reduction potential tells us that it is harder to reduce (worse oxidizing agent)
• In any voltaic cell operating under standard conditions: ❑ the E°red value for the reaction at the cathode is more positive than the E°red value for the reaction at the anode. ❑ electrons flow through the external circuit from the electrode with the more negative value of E°red to the electrode with the more positive value of E°red.
• The one with the highest reduction potential will be the reduction half-reaction and is the cathode. The one with the lowest reduction potential will be the oxidation-half reaction and is the anode