The reaction between chlorine and potassium bromide solution is a displacement reaction, where chlorine, a more reactive halogen, displaces bromine from its salt. This chemical change is accompanied by a distinct colour transformation.
The various forms of the chemical equation for this reaction are presented below:
| Type of Equation | Equation |
|---|---|
| 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) |
Observations During the Reaction
Initially, the potassium bromide solution is colourless. As chlorine gas is introduced and reacts with the solution, you will observe the solution changing to a brown colour. This visual change indicates the formation of aqueous bromine (Br₂(aq)) as a product of the reaction.
Understanding the Reaction and Its Components
This reaction is a classic example of a halogen displacement reaction, which demonstrates the reactivity trend within Group 7 of the periodic table.
- Chlorine (Cl₂): A reactive, pale greenish-yellow gas. In this reaction, it acts as the displacing agent.
- Potassium Bromide (KBr): A soluble salt that provides bromide ions (Br⁻) in its colourless aqueous solution.
- Bromine (Br₂): A reddish-brown liquid. When formed in an aqueous solution, it imparts a characteristic brown colour.
- Potassium Chloride (KCl): A soluble salt that forms a colourless solution. The potassium ions (K⁺) are spectator ions and do not participate directly in the chemical change, which is why they are omitted from the ionic equation.
The underlying principle is that chlorine is more reactive than bromine. Elements higher up in Group 7 are more reactive, meaning they have a greater ability to gain electrons. Therefore, chlorine can readily accept electrons from bromide ions, oxidizing the bromide ions to form bromine and becoming reduced itself to chloride ions.
