Some reactions of the halide ions

Need to know

What you need to know

• **Chloride (Cl⁻):** Forms a **white** precipitate of silver chloride (AgCl).
• **Bromide (Br⁻):** Forms a **cream** precipitate of silver bromide (AgBr).
• **Iodide (I⁻):** Forms a **yellow** precipitate of silver iodide (AgI).

Explanation

Halide Identity Parade

1. Test for halide ions using acidified silver nitrate. Observe the precipitate colours: AgCl is white, AgBr is cream, and AgI is yellow.
2. Observe the reaction with concentrated sulfuric acid. Iodide ions are strong enough reducing agents to reduce H₂SO₄ to H₂S, S, and SO₂.
3. Recognise that the reducing power of halide ions increases down the group (I⁻ > Br⁻ > Cl⁻) as the outermost electron is easier to remove.
4. See how a more reactive halogen displaces a less reactive halide from solution, e.g., chlorine displaces iodide ions to form iodine.