What Is Redox ?


Reduction - Oxidation (redox) -- The CHEMICAL changes that occur when

ELECTRONS are transferred between reactants.


OXIDATION -- Originally it meant the combination of an element with oxygen to give oxides,

now it means the LOSS of ELECTRONS or the gain of oxygen.


REDUCTION -- It has meant the loss of oxygen from a compound, now

it means the GAINING of ELECTRONS or the loss of oxygen.


These two processes occur at the same time.


Example :


Mg + S à MgS


oxidation Mg 0 à Mg +2 + 2 e -


half reaction


reduction S 0 + 2 e - à S -2

half reaction


Oxidation numbers The CHARGE assigned to an element.


The charge of a uncombined element is 0 .


In most compounds, the charge of hydrogen is +1 .

In most compounds, the charge of oxygen is -2 .

The sum of charges in a NEUTRAL molecule is zero.


Using oxidation numbers and brackets identify the oxidation part of the reaction, the reduction part of the reaction, and how many electrons are lost and gained. Write the oxidation half reaction and the reduction half reaction.




Electrochemistry is an application of reduction-oxidation processes.


Electrochemical Cells -- Any devices used to convert CHEMICAL energy

into ELECTRICAL energy.


The Device


Half-cell -- A PART in which either the OXIDATION half of the

reaction or the REDUCTION half of the reaction occurs.


Electrodes -- They are CONDUCTORS in a CIRCUIT that carry

electrons to or from a substance.


ANODE -- The electrode at which OXIDATION occurs,

electrons are PRODUCED here, it is labeled

the NEGATIVE electrode.


CATHODE -- The electrode at which REDUCTION occurs,

electrons are CONSUMED here, it is labeled

the POSITIVE electrode.


Salt BRIDGE -- A PART that completes the circuit. It made

with a conducting solution.

Making An Electrochemical Device

Problem : Make a complete electrochemical cell




1. Write the oxidation half reaction and the reduction half reaction for the cell above.




2. Define in your own words the following: salt bridge, anode, cathode, and electricity.