Properties of Halogens - Reactions Between Halogens and Halide Ions


	Part II: Reactions Between Halogens and Halide Ions
	In this experiment we will test all six combinations of different halogens (Cl₂, Br₂, and I₂) and halides (Cl^-, Br^-, and I^-) to see which ones will react and which ones won't. In our example here, we will look at the possible reaction between the halogen Br₂ and the halide ions Cl^- and I^-. To do this for Br₂, for example, we first take two 13 X 100 mm test tubes and add 10 drops of 0.2 M NaCl solution to one and 10 drops of 0.2 M NaI solution to the other. We then add 10 drops of hexanes to each test tube to form a hexanes layer on top of the aqueous solutions. Observe the color of the hexanes layer before addition of Br₂ and record it on your data sheet. The photos below illustrate our results so far.

	Then 10 drops of bromine water are added to each test tube. The tubes are stoppered with corks obtained from the stockroom and shaken to ensure mixing of the two possible reactants. After shaking the tubes vigorously, allow them to settle for about one minute. Observe the color of the hexanes layer and record it on your data sheet. The photo below shows the results of this stage of the experiment. Notice that in both cases a color appears in the hexanes layer, although not the same color. Use the color in the hexanes layer to determine if a reaction occurred between the halogen and the halide ion. IMPORTANT NOTE: Just because a color is present in the hexane layer, do not assume that a reaction has occurred. The color must also match the color of the halogen expected as the product in the possible reaction. To help determine if a reaction has occurred, write the equation for the possible reaction on the data sheet. For example, for the possible reaction between Br₂and Cl^- the equation would be: Br₂ + 2Cl^- -------> 2Br^- + Cl₂. In this case, if the color in the hexanes layer matches the color of Cl₂, the product halogen in this case, then a reaction has occurred. But if the color of the hexanes layer matches the color of Br₂, the reactant halogen in this case, then NO REACTION occurred.

	Of the six possible reactions you will test, three will work and three will not react. Furthermore, you will find that you can group the possible reactions into pairs in which the chemical equation for one possible reaction is the reverse of the other. Only one possible reaction in each pair will work, the other will not. Once all your results are in, see if they agree with what you know about electronegativity trends. In each possible reaction, two halogen elements are competing over which one gets to have the extra electron. Does the more electronegative halogen element get to keep an extra electron for all of your halogen-halide combinations? Don't forget to dump ALL of your hexanes waste into the "Hexane Waste" beaker in the fume hood.