Halogen Displacement & Redox (Edexcel GCSE Chemistry)
Revision Note
Halogen Displacement & Redox
Recall that oxidation and reduction take place together at the same time in the same reaction
Oxidation is loss of electrons and reduction is the gain of electrons
Halogen displacement reactions are redox reactions
This can be seen if we analyse in more detail the displacement of iodine by chlorine in the following reaction:
CI2 + 2Kl ⟶ 2KCI + l2
chlorine + potassium iodide ⟶ potassium chloride + iodine
The full ionic equation is:
CI2 + 2K+ + 2l- ⟶ 2K+ + 2CI- + l2
The K+ ions are spectator ions as they appear on both sides of the equation unchanged so can be eliminated. The net ionic equation is thus:
CI2 + 2l- ⟶ 2CI- + l2
If we now analyse each half equation, we can see that each chlorine atom has been reduced as an electron is gained on changing from the chlorine molecule to chloride ions:
CI2 + 2e- ⟶ 2CI- REDUCTION
Each iodide ion has been oxidised as an electron is lost on changing from iodide ions to the iodine molecule:
2l- ⟶ I2 + 2e- OXIDATION
This shows that halogen displacement reactions are redox processes
Examiner Tips and Tricks
The more reactive halogen undergoes reduction, the less reactive one undergoes oxidation.
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