The ionic equation for the reaction between chlorine and aqueous potassium bromide solution is Cl₂(g) + 2Br⁻(aq) → Br₂(aq) + 2Cl⁻(aq).
Understanding the Reaction Between Chlorine and Potassium Bromide
This chemical reaction is a classic example of a halogen displacement reaction, where a more reactive halogen displaces a less reactive halogen from its compound. In this case, chlorine, being more reactive than bromine, displaces bromine from potassium bromide.
The observable change during this reaction is that the initial colourless potassium bromide solution transforms into a brown solution as bromine is formed.
Equations for the Reaction
To fully understand the ionic equation, it's helpful to first look at the word and symbol equations.
| Equation Type | Representation |
|---|---|
| Word Equation | Chlorine + Potassium Bromide → Bromine + Potassium Chloride |
| Symbol Equation | Cl₂(g) + 2KBr(aq) → Br₂(aq) + 2KCl(aq) |
| Ionic Equation | Cl₂(g) + 2Br⁻(aq) → Br₂(aq) + 2Cl⁻(aq) |
Deriving the Ionic Equation
The full symbol equation, Cl₂(g) + 2KBr(aq) → Br₂(aq) + 2KCl(aq), includes all substances involved. However, in an aqueous solution, ionic compounds like potassium bromide (KBr) and potassium chloride (KCl) dissociate into their respective ions.
- Potassium bromide (KBr) exists as K⁺(aq) and Br⁻(aq) ions in solution.
- Potassium chloride (KCl) exists as K⁺(aq) and Cl⁻(aq) ions in solution.
When we write the complete ionic equation, we show all dissolved ions:
Cl₂(g) + 2K⁺(aq) + 2Br⁻(aq) → Br₂(aq) + 2K⁺(aq) + 2Cl⁻(aq)
Notice that the potassium ions (K⁺) appear on both sides of the equation. These are known as spectator ions because they do not participate directly in the chemical change; they simply remain in solution. To obtain the net ionic equation, we remove these spectator ions.
By removing the 2K⁺(aq) from both sides, we are left with the simplified ionic equation that shows only the species that undergo a change:
Cl₂(g) + 2Br⁻(aq) → Br₂(aq) + 2Cl⁻(aq)
This ionic equation clearly illustrates that gaseous chlorine reacts with aqueous bromide ions to produce aqueous bromine and aqueous chloride ions. This conversion highlights the redox nature of the reaction, where chlorine is reduced (gains electrons) and bromide ions are oxidized (lose electrons).
