Halogen Displacement

Materials: ★★★ Requires materials not commonly found in school laboratories
Difficulty: ★★☆ Can be done by science teachers
Safety: ★★★ Only to be attempted with adequate safety procedures and trained staff

Categories: Elements and Periodic Table

Alternative titles: Halogen Reactivity Series

Summary

Different halogen solutions are reacted with potassium halide salts to observe displacement reactions. The outcomes illustrate the relative reactivity of halogens and help establish the halogen reactivity series.

Procedure

Place a few drops of each potassium halide salt solution (KCl, KBr, KI) into separate wells on a spotting tile.
Add a few drops of chlorine water to each well and observe any changes.
Repeat the process using bromine water and iodine water, testing each halogen solution against all three halide salts.
Look for color changes, precipitate formation, or fading of color (distinguishing real reactions from dilution).
Test the pH of each well with universal indicator paper.
Compare results to determine which halogen has displaced another.

Links

Halogen Displacement Reactions - Royal Society of Chemistry:

Displacement of Halogens - Rugby School Chemistry:

📄 Halogen Displacement - Practical Science: https://practical-science.com/2023/04/08/halogen-displacement/

Variations

Record the intensity of color changes using a color chart for more precise comparisons.
Extend the experiment with sodium halide salts to confirm consistency across different cations.
Use cyclohexane as an organic solvent to extract displaced halogens (especially iodine and bromine) for clearer visualization.

Safety Precautions

Wear safety goggles and a lab coat at all times.
Handle chlorine, bromine, and iodine solutions with care; they can be irritants or toxic.
Perform the experiment in a well-ventilated area or fume hood.
Avoid direct contact with chemicals; use droppers and gloves.
Dispose of waste solutions properly according to school or local safety guidelines.

Questions to Consider

Which halogens displaced others in the reactions? (Chlorine displaces bromide and iodide; bromine displaces iodide; iodine does not displace others.)
How does this experiment support the halogen reactivity series? (Reactivity decreases down Group 17: Cl₂ > Br₂ > I₂.)
Why might color changes be more visible in certain reactions? (Different halogens form solutions with distinctive colors, e.g., iodine brown, bromine orange.)
How does this experiment demonstrate oxidation and reduction? (The more reactive halogen is reduced to halide ions, while the less reactive halide is oxidized to elemental halogen.)