Complex ion-electron equations and example

Understanding Complex Ion-Electron Equations:

Complex ion-electron equations are chemical equations that involve not only ions and electrons but also hydrogen ions (H⁺) and water (H₂O). These equations are used to describe complex redox reactions in which multiple species are involved.

Use of Data Booklet:

• The data booklet often provides examples of complex ion-electron equations for common reactions.
• However, it may be necessary to write these equations when they are not provided in the data booklet.

Steps for Writing Complex Ion-Electron Equations:

• To write complex ion-electron equations, follow these steps:

Example: Reduction of Dichromate Ions to Chromium(III) Ions

• Let's consider the example of the reduction of dichromate ions to chromium(III) ions.

Basic Change:

• Begin with the basic change involved in the reaction:
• Cr₂O₇²⁻(aq) → Cr³⁺(aq)

Balancing Chromium Ions:

• Balance the number of chromium ions on both sides:
• Cr₂O₇²⁻(aq) → 2Cr³⁺(aq)

Balancing Oxygen with Water:

• Since there is oxygen on the left side, balance it by adding water molecules to the right side:
• Cr₂O₇²⁻(aq) + 7H₂O(l) → 2Cr³⁺(aq)

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Bonding Continuum

Balancing Oxygen with Water:

• The addition of water introduces hydrogen, which also needs to be balanced:
• $Cr_2O_7^{2-}(aq) + 14H_2O(l) \rightarrow 2Cr^{3+}(aq) + 14H^+(aq)$

Balancing Charge:

• Finally, ensure that the electric charge is balanced on both sides:
• On the left side, the overall charge is 12+ (from the negative dichromate ion and positive hydrogen ions).
• On the right side, it is 6+ (from the two chromium ions).
• To balance the charge, add electrons (e⁻) to the left side:
• $Cr_2O_7^{2-}(aq) + 14H_2O(l) + 6e^- \rightarrow 2Cr^{3+}(aq) + 14H^+(aq)$