Materials Included In Kit

Additional Materials Required

Safety Precautions

Silver nitrate is highly toxic and causes burns, avoid contact with eyes and skin. Hexanes is a flammable liquid, a dangerous fire risk and may be irritating to the respiratory tract. Sodium hypochlorite solution is corrosive, moderately toxic by ingestion and inhalation, causes skin burns, reacts with acid to give off chlorine gas and evolves chlorine when heated. Hydrochloric acid is toxic by ingestion or inhalation and is severely corrosive to skin and eyes. Ammonium hydroxide is moderately toxic by ingestion and inhalation, irritating to the eyes and is a serious respiratory hazard. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Hexanes should be treated according to Flinn Suggested Disposal Method #18a. Silver nitrate should be precipitated according to Flinn Suggested Disposal Method #11. Hydrochloric acid should be neutralized according to Flinn Suggested Disposal Method #24b. The solution from part B should be placed in an operating fume hood and allowed to degas (to remove any Cl₂, Br₂ or I₂). Once the hexane is colorless, it may be treated according to Flinn Suggested Disposal Method #18A. All other solutions may be flushed down the drain with excess water according to Flinn Suggested Disposal Method #26b.

Teacher Tips

• With respect to the solids—NaCl, NaBr and NaI—be sure to remind the students to use only about one-half of a match head in each test tube.
• To make chlorine water: mix about 2 mL of laundry bleach or sodium hypochlorite solution (Clorox Bleach) with 2 mL of a 5 M hydrochloric acid. Then dilute to 15 mL with distilled or deionized water. This should be enough for a class of about 15 groups (30 students).
• The chlorine water should be made up the same day it will be used and can be disposed of by allowing it to stand in an open container inside an operating fume hood. The chlorine will slowly leave the water and the container. The remaining water (now effectively degassed) can be put down the drain.
• To help identify the halide ions—A white precipitate is formed upon adding a silver nitrate solution indicating the presence of a chloride. Silver chloride is readily soluble in ammonium hydroxide (NH₄OH) and is reprecipitated by the addition of dilute nitric acid. A cream-colored precipitate, soluble only in a large excess of ammonia water, shows the presence of bromide ions. A yellow precipitate, insoluble in ammonium hydroxide, indicates an Iodide.
• When chlorine water is added to a solution of bromide or iodide ions, a redox reaction occurs that effectively converts the chlorine (Cl₂) and bromide (or iodide) into chloride ions (Cl^–) and elemental bromine (or iodine). Elemental bromine (Br₂) or iodine (I₂) are nonpolar and are more soluble in the hexane layer than the water layer and are clearly visible due to the color change in the hexane layer.

Answers to Questions

Part 1

1. What effect does the silver nitrate have upon the halogen salt solutions?

   The chemical reaction between the halogen salt solutions and the silver nitrate produces a precipitate (white with chloride, light cream with bromide and pale yellow with iodide).

2. What effect does the ammonia water (ammonium hydroxide) have upon the silver chloride, silver bromide, and silver iodide precipitates?

   The ammonia water dissolves the silver chloride, but does not seem to dissolve silver bromide or silver iodide.

3. Complete the following equations

   AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

   AgNO₃(aq) + NaBr(aq) → AgBr(s) + NaNO₃(aq)

   AgNO₃(aq) + NaI(aq) → AgI(s) + NaNO₃(aq)

1. Record your observations and conclusion of the unknown halide below.

   Answers will vary depending on what halogen salt is given.

Introduction

In this experiment, several techniques will be used to identify three types of halides: chloride, bromide and iodide ions. Finally, an unknown halide salt or a mixture of halide salts will be identified.

Concepts

• Qualitative analysis
• Finding an unknown halide

Background

Qualitative analysis is the identification of materials and is an important aspect of chemistry. Traditional qualitative analysis procedures use wet chemistry methods such as precipitation, titration, and solvent extraction to identify an element, compound, or mixture of compounds. Newer qualitative analysis procedures use analytical instruments to identify substances. Understanding the fundamental properties of an element or substance is important in developing qualitative analysis procedures.

In this laboratory activity, qualitative analysis procedures will be used to identify three common halide ions: chlorides, bromides, and iodides. In the first procedure, a precipitation reaction will be used. Careful observation of the precipitates may result in positive identification of the three different halides. In the second procedure, a redox reaction and solvent extraction procedure will be used to provide a more definitive identification of the three different halides. After the qualitative analysis procedures have been perfected on known materials, an unknown halide or mixture of halides will be identified.

Materials

Safety Precautions

Silver nitrate is highly toxic and causes burns. Avoid contact with eyes and skin. Hexanes is a flammable liquid, a dangerous fire risk and may be irritating to the respiratory tract. Sodium hypochlorite solution is corrosive, moderately toxic by ingestion and inhalation, causes skin burns, reacts with acid to give off chlorine gas and evolves chlorine when heated. Hydrochloric acid is toxic by ingestion or inhalation and is severely corrosive to skin and eyes. Ammonia water is moderately toxic by ingestion and inhalation, irritating to the eyes and is a serious respiratory hazard. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Part 1

1. Label three small test tubes with the letters C, B, and I representing chloride ions, bromide ions, and iodide ions, respectively.
2. In each of the test tubes place a small amount of common salt about the size of one-half a match head. For the test tube labeled C, use sodium chloride (NaCl); the test tube labeled B, use sodium bromide (NaBr); the test tube labeled I, use sodium iodide (NaI).
3. Now place 20 drops of distilled water into each test tube. Stopper and shake the contents until all of the solid has dissolved.
4. Now place five drops of silver nitrate into each test tube. Stopper and shake the contents once again. Which solutions form a precipitate? Record the observations.
5. Finally place 20 drops of ammonia water (ammonium hydroxide) into each test tube. Stopper and shake the contents once again. Which precipitates dissolve? Record the observations.
6. Clean and dry the three test tubes for use in Part II.

7. Once again, label three small test tubes with the letters C, B and I representing chloride ions, bromide ions, and iodide ions, respectively.
8. In each of the test tubes place a small amount of common salt about the size of one-half a match head. For the test tube labeled C, use sodium chloride (NaCl); for the test tube labeled B, for use sodium bromide (NaBr); the test tube labeled I, use sodium iodide (NaI).
9. Into each of these test tubes, place 20 drops of water. Stopper and shake the contents until all of the solid has dissolved.
10. Now add 20 drops of hexanes to each of the test tubes, stop per, shake the contents, and let settle. Two layers of liquid will appear; the top layer will be the hexanes. Note the color of the hexanes layer.
11. Place about 10 drops of chlorine water into each test tube. Stopper and shake the contents. Observe the color of the hexane layer. Has the color changed? Record your observations. Caution: Chlorine water is toxic. Avoid direct contact. To remove from skin, wash thoroughly with water.

12. Obtain from your teacher an unknown halogen salt and determine its halide. Record your observations and conclusion.
13. See the instructor for appropriate disposal procedures.

Student Worksheet PDF

12570_Student1.pdf