Redox Reactions
Identifying redox reactions
- Redox reactions can be identified by the changes in the oxidation states when a reactant goes to a product
Example
Chlorine + potassium iodide → potassium chloride + iodine
Cl2 + 2KI → 2KCl + I2
- Chlorine has become reduced as its oxidation state has decreased from 0 to -1 on changing from the chlorine molecule to chloride ions:
Cl2(g) → 2Cl-(aq)
- Iodine has been oxidised as its oxidation state has increased from -1 to 0 on changing from iodide ions to the iodine molecule:
2I-(aq) → I2(s)
Identifying redox reactions by colour changes
- The tests for redox reactions involve the observation of a colour change in the solution being analysed
- Two common examples are acidified potassium manganate(VII), and potassium iodide
- Potassium manganate (VII), KMnO4, is an oxidising agent which is often used to test for the presence of reducing agents
- When acidified potassium manganate (VII) is added to a reducing agent its colour changes from pink-purple to colourless
- Potassium iodide, KI, is a reducing agent which is often used to test for the presence of oxidising agents
- When added to an acidified solution of an oxidising agent such as aqueous chlorine or hydrogen peroxide, the solution turns a brown colour due to the formation of iodine
