Oxidation/Reduction Reaction examples

Use your clickers to answer

A piece of clean copper is placed in a solution of silver nitrate. Assuming the copper goes to Cu(II) write a balanced equation. Notice that in this case you must balance the charge in order to get the final equation.

First need to write out the reactant species.

What is the charge of copper?

Cu^?

 

What is the charge of the silver ion?

Ag^?

 

What is the charge on nitrate ion?

NO_3^?

 

Next figure out charge on product ions

What is the charge on Copper ion?

Cu^?

 

What is the charge on silver?

Ag^?

 

 

Now write balanced equation.

As another example we can look at a key oxidation reaction in glycolysis, the central pathway of metabolism. Don't worry about these reactions - they will not be on an exam. They are presented for your interest. In this case we use a biological oxidizing agent, NAD+ to take electrons (in the form of a hydride ion, H:-) Frequently organisms need to operate this reaction under anaerobic (oxygen free) conditions. For example the maximum power (energy/sec) you can get from your muscles is anaerobically. For this to occur you need to regenerate the oxidizer (NAD+) without the presence of oxygen. For this to occur we use another reaction: The mechanism for this electron transfer is shown below:

The Half-Reaction Method

In the half-reaction method what we do is first break an equation into two parts and then balance the parts individually. Presented stepwise:

• Separate the reaction into two half-reactions.
• Balance each half-reaction separately:
  1. Balance atoms other than O & H by inspection.
  2. Balance O by adding H₂O to the opposite side.
  3. Balance H:
     • In acid solution add H⁺ as appropriate.
     • In base solution add H₂O to the side needing H, balance O by adding equal numbers of OH^- to the opposite side.
  4. Balance the charge by adding electrons (e^-) - add to same side as excess of positive charge, or opposite side if excess negative charge.
• Balance the charges of the two half-reactions by multiplying appropriately, then add to two equations together and cancel items appearing on both sides.

© R A Paselk

Last modified 9 December 2009