Halogen/Halide Redox Reactions
An aqueous solution of a halogen (Cl2, Br2 or I2) is poured into an aqueous halide solution (Cl-, Br- or I-) covered with a layer of hexane. After the liquid has been shaken, the color of the hexane layer is compared to the color of hexane solutions of chlorine, bromine and iodine. Six combinations of halide with halogen are shown.
(86 )
Keywords
descriptive chemistry, halogens/halides/hydrohalic acids, periodic table/trends, redox reaction
Multimedia
A series of aqueous halide solutions (Cl-(aq ), Br-(aq ) or I-(aq )) are poured into an aqueous solution of a halogen that is covered with a layer of hexane. Solutions of chlorine, bromine, and iodine are shown here for later reference.
 |
Bromide added to Chlorine
Play movie
(QuickTime 3.0 Sorenson, duration 16 seconds, size 1 MB)
Bromide ion is added to chlorine water. By observing the color of the hexane layer, we see that the reaction has produced bromine.
(Note that the hexane layer is above the aqueous layer.)
2Br-(aq ) + Cl2(aq ) --> 2Cl-(aq ) + Br2(aq )
 Bromide ion is added to chlorine water |
 ... and is shaken. |
 The reaction has produced bromine. |
Additional still images for this movie
Iodide added to Chlorine
Play movie
(QuickTime 3.0 Sorenson, duration 15 seconds, size 1020 K)
Iodide ion is added to chlorine water. By observing the color of the hexane layer, we see that the reaction has produced iodine.
(Note that the hexane layer is above the aqueous layer.)
2I-(aq ) + Cl2(aq ) --> 2Cl-(aq ) + I2(aq )
 Iodide ion is added to chlorine water |
 ... and is shaken. |
 The reaction has produced iodine. |
Additional still images for this movie
Chloride added to Bromine
Play movie
(QuickTime 3.0 Sorenson, duration 13 seconds, size 870 K)
Chloride ion is added to bromine water. By observing the color of the hexane layer, we see that no reaction has occurred.
(Note that the hexane layer is above the aqueous layer.)
2Cl-(aq ) + Br2(aq ) --> No reaction took place
 Chloride ion is added to bromine water |
 ... and is shaken. |
 No reaction took place. |
Additional still images for this movie
Iodide added to Bromine
Play movie
(QuickTime 3.0 Sorenson, duration 15 seconds, size 1 MB)
Iodide ion is added to bromine water. By observing the color of the hexane layer, we see that the reaction has produced iodine.
(Note that the hexane layer is above the aqueous layer.)
2I-(aq ) + Br2(aq ) --> 2Br-(aq ) + I2(aq )
 Iodide ion is added to bromine water |
 ... and is shaken. |
 The reaction has produced iodine. |
Additional still images for this movie
Chloride added to Iodine
Play movie
(QuickTime 3.0 Sorenson, duration 13 seconds, size 900 K)
Chloride ion is added to iodine water. By observing the color of the hexane layer, we see that no reaction has occurred.
(Note that the hexane layer is above the aqueous layer.)
2Cl-(aq ) + I2(aq ) --> No chemical reaction took place
 Chloride ion is added to iodine water |
 ... and is shaken. |
 No chemical reaction took place. |
Additional still images for this movie
Bromide added to Iodine
Play movie
(QuickTime 3.0 Sorenson, duration 13 seconds, size 900 K)
Bromide ion is added to iodine water. By observing the color of the hexane layer, we see that no reaction has occurred.
(Note that the hexane layer is above the aqueous layer.)
2Br-(aq ) + I2 --> No chemical reaction took place
 Bromide ion is added to iodine water |
 ... and is shaken. |
 No chemical reaction took place. |
Additional still images for this movie
Discussion
This series of movies can be used to allow students to discover the order of oxidizing ability of the halogens. Students could be asked to select a reaction and that reaction could be shown. Based on whether there is a color change, students could whether each of the possible reactions takes place, thereby showing that chlorine reacts with bromide and iodide, bromine reacts with iodide, and iodine does not react with either of the other halide ions.
Demonstration Notes, Warnings, Safety Information, etc.
Exam and Quiz Questions
1. How can you tell whether or not a reaction has occurred in a vial?
2. Which halogen is most reactive, Br2, Cl2, or I2? Which halogen is least reactive? Explain.
3. Write balanced chemical equations for the reactions occurring in each vial. Write NR if no reaction took place.