What’s that blue stuff?
The reaction of copper wire with nitric acid produces a colorful mix of products that include copper(II) nitrate, nitrogen dioxide, and water. Copper salts are blue in solution, reflecting the rather unique arrangements of electrons in the
Identifying Reaction Types
A redox reaction must involve a change in oxidation number for two of the elements involved in the reaction. The oxidized element increases in oxidation number, while the reduced element decreases in oxidation number.
Single-replacement reactions are redox reactions because two different elements appear as free element (oxidation number of zero) on one side of the equation and as part of a compound on the other side. Therefore, its oxidation number must change.
Zn is oxidized from Zn 0 to Zn 2+ and the H is reduced from H + to H 0
Combustion reactions are redox reactions because elemental oxygen (O 2 ) acts as the oxidizing agent and is itself reduced.
Most combination and decomposition reactions are redox reactions since elements are usually transformed into compounds and vice-versa. The thermite reaction involves ferric oxide and metallic aluminum:
We see that the iron is reduced and the aluminum oxidized during the course of the reaction.
Watch a video of the thermite reaction:
Note that the oxidation numbers for each element remain unchanged in the reaction.
Acid-base reactions involve a transfer of a hydrogen ion instead of an electron. Acid-base reactions, like the one below, are also not redox reactions.
Again, the transfer of an H + ion leaves the oxidation numbers unaffected. In summary, redox reactions can always be recognized by a change in oxidation number of two of the atoms in the reaction. Any reaction in which no oxidation numbers change is not a redox reaction.
- Criteria for determining whether or not a reaction involves oxidation and reduction are listed.
Indicate which of the following reactions are redox reactions and which are not:
You do not need to write explanations or balance the equations.
- Why is the Zn + HCl reaction a redox reaction?
- Why is the sodium sulfate + barium nitrate reaction not a redox reaction?
- Does the transfer of H + affect oxidation numbers?