Combining Simple Redox Equations

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Combining Oxidation and Reduction reactions

A redox equation is obtained by combining oxidation and reduction half equations.
In order that the equations balance, the number of electrons lost in the oxidation reaction must be equal to the number of electrons gained in the reduction reaction.

A table known as the standard reduction potential series gives many of the reactions you are likely to need.

Red-brown copper metal displaces grey silver metal when added to a colourless solution of silver(I) nitrate. During the reaction, the solution turns blue as copper(II) ions are made.

Copper changes into copper(II) ions while silver(I) ions change into silver atoms.

Data provides the following reduction reactions:

 

1. Cu2+(aq) + 2e- ---> Cu(s)

 

2. Ag+(aq) + e- ---> Ag(s)

Equation (1) will have to be reversed to show copper metal undergoing oxidation.

 

(1) Cu(s) ---> Cu2+(aq) + 2e-

 

(2) Ag+(aq) + e- ---> Ag(s)

Equation (2) will have to be doubled to make sure both electrons lost by each copper atom are gained.

 

(1) Cu(s) ---> Cu2+(aq) + 2e-

 

(2) 2Ag+(aq) + 2e- ---> 2Ag(s)

The equations can now be added together and the electrons will 'cancel out' to given the combined redox equation:

 

Cu(s) + 2Ag+(aq) ---> Cu2+(aq) + 2Ag(s)