Colored Halogene Displacement Reaction

Two layer mixtures change color.

Scientific name: Halogens displace each other from compounds according to their activity.

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Safety

Wear eye protection goggles. Care with chlorine and bromine solutions. Perform experiment in well ventilated room.

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

KF + Cl2 → no reaction

KCl + Cl2 → no reaction

2KBr + Cl2 → 2KCl + Br2

2KI + Cl2 → 2KCl + I2

KF + Br2 → no reaction

KCl + Br2 → no reaction

KBr + Br2 → no reaction

2KI + Br2 → 2KBr + I2

Step-by-step instruction

  1. Prepare four test tubes.
  2. Pour a few milliliters of cyclohexane into each test tube.
  3. Add the solution of potassium fluoride to the first test tube.
  4. The cyclohexane is on top of the mixture.
  5. Repeat the procedure with other test tubes and solutions of potassium chloride, potassium bromide and potassium iodide.
  6. Add some chlorine water to each test tube.
  7. Solutions in the first and second test tubes with potassium fluoride and potassium chloride respectively stay unchanged.
  8. The water solution in the third test tube turns pale yellow.
  9. The top layer in the last test tube turns violet and the bottom layer turns yellow.
  10. Prepare four test tubes with initial two-layer mixtures of metal halide solutions and cyclohexane.
  11. Add some bromine water to each test tube.
  12. The bottom layer in all test tubes besides the last one turns yellow. The bottom layer in the last test tube becomes dark-purple.

Scientific background

In this experiment the displacement halogen reactions are demonstrated. The halogen’s activity and ability to displace each other from compounds changes according to their position in periodic table. Reactivity decreases down Group 7. On atomic level it means that the larger the radius of the halogen atom the less activity it possess. Fluorine is the most reactive halogen. Chlorine is less reactive than fluorine but more reactive than bromine. Iodine is the least active. Thus in the first part of the experiment chlorine dissolved in water displaces bromine and iodine ions and has no impact on potassium fluoride solution. Bromine and iodine move out of the compound and come to the top layer, since halogens are more soluble in cyclohexane than in water. Small concentration of bromine turns the solution yellow as well as small concentration of iodine makes the solution violet.

In the second part of the experiment bromine water is tested for the halogen displacement reactions. Similarly to the case of chlorine water and potassium fluoride, bromine could not displace fluorine and chlorine ions from their compounds. Reaction is possible only in the case of the least active iodine.

Danger:
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Published on 14 May 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst