688

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uOnanp°.IlUI

340 Experiment 19A

has its own characteristic color,depending on the concentration and thicknessof the solution. Chlorine water is colorless to yellow; bromine water is yellowto red-brown; and iodine water is red-brown to brown.

These halogens are also soluble in cyclohexane (C6H12),a substance that is it-self insoluble in water. When cyclohexane is added to an aqueous solution of ahalogen, two layers are formed. The upper layer is cyclohexane, because it isinsoluble and less dense than water. A portion of the halogen passes from theaqueous layer to the upper cyclohexane layer (a process called extraction). Acharacteristic color is then imparted to this layer. The color of a halogen in cy-clohexane differs somewhat from its color in an aqueous solution, as you willdiscover during the experiment.

Reduction of a halogen (x2) yields halide ions (X-) according to the half-reaction.

Because the halogens are oxidizing agents, the halide ions are reducingagents. Compounds of the halides are colorless if the positive ions belong to ei-ther Group IA or Group IIA, as in Nal or CaCI2.Compounds of this type areionic, so they are insoluble in cyclohexane.

Reduction of other common oxidizing agents

You will also encounter two other oxidizing agents in this experiment. Theseare KMn04 (potassium permanganate) and FeCI3•

Reduction of purple Mn04- can give either green Mn042- (manganate ion);brown-black Mn02, which will be a solid; or Mn2+,an ion that is pink but willbe virtually colorless at the concentration found in this experiment. ReductionofFe3+ will give Fe2+,a pale green ion that will be virtually colorless at the con-centration found in this experiment.

Concept of the experiment

You will mix aqueous solutions of potential oxidizing and reducing agents ineach part of this experiment. However, do not expect a reaction to occur inevery mixture that you prepare. If a reaction occurs, there will be certain tell-tale signals. The formation or disappearance of the characteristic color of oneof the halogens in a cyclohexane layer is usually a signal of a reaction in theaqueous layer. In some instances, color changes in the aqueous layer will alsoindicate that a reaction has occurred.

Procedure

Getting started

1. Obtain 3 large test tubes with stoppers for the halogen solutions, 3 smalltest tubes, and one piece of fine filter paper.

2. Label the large test tubes so that you will know which halogen each onecontains.

3. Obtain directions for discarding the solutions that you use during theexperiment.

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l h

342 Experiment 19A

4. Add 5 drops of 3 M H2S04 to each test tube.5. Add about 1 mL of cyclohexane to each test tube. Shake or swirl the test

tubes very gently, and then record your observations for both layers.6. Repeat Steps 1 through 5, using 8 drops of 0.4 M Nal instead of 15 drops of

0.2MNaBr.7. Wash and dry one of the test tubes.8. Add 8 drops of 0.4 M Nal, 5 drops of 6 M NaOH, 1 drop of 0.1 M KMn04,

and about 1 mL of cyclohexane to this test tube. Shake or swirl very gentlyand record your observations for both layers.

9. Dispose of the halogen solutions according to the directions provided byyour laboratory instructor.

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.(;

x''17

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....348 Experiment 1.9A

3. Reactions of other common oxidizing agents in acidic solution

Br I

7.

10.

9.

8.

4. Reaction o{MnOl with I in basic solution

I

11.

Questions

1. You have made 11 observations. Each one has been numbered. Thisquestion asks you to consider the first 10. Indicate those cases in whichno reaction occurred. If a reaction occurred, write a balanced equationthat is in accord with your observation.

(1)

(2)

continued

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