Materials Included In Kit

Additional Materials Required

Safety Precautions

Silver nitrate solution will stain skin and clothing. Avoid contact with eyes and skin. Sodium hydroxide solution is corrosive; very dangerous to skin and eyes. Ammonium nitrate solution is toxic by ingestion; skin, eye and respiratory irritant. Wear chemicalresistant apron, chemical-resistant gloves and chemical splash goggles. Please review current Safety Data Sheets for additional safety, handling and disposal information. Immediately dispose of the unreacted mixture. Explosive fulminating silver compounds may form if the unreacted mixture is allowed to stand.

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. The mixture remaining in the flask after the silver mirror reaction is complete should be rinsed with excess water into a waste disposal beaker or flask set up in a central location. Test the combined waste solution for the presence of leftover silver ions by adding 1 M hydrochloric acid. If a cloudy, white precipitate of silver chloride is observed, continue adding hydrochloric acid in small amounts until no further precipitation is evident. Filter the mixture—the silver chloride may be packaged for landfill disposal according to Flinn Suggested Disposal Method #26a. The filtrate may be disposed of down the drain with plenty of excess water according to Flinn Suggested Disposal Method #26b.

Teacher Tips

• Rinse the tube with acetone before the mirror is made to improve the quality of the mirror. Be sure to air dry the tube to completely remove all the acetone.
• Students can make several of the mirrored tubes and glue small corks in them to make earrings to take home. Try this activity right before Christmas so the students can make several different items. Students can make pendants, necklaces, tree ornaments, earrings, etc.
• The silver coating on the inside of the test tubes may be protected from oxidation and mechanical stress by giving the inside a coating of clear shellac or clear nail polish.
• If you are using old test tubes, rinse them first with distilled water. Taking care to keep the acid off your skin, rinse again with a ¼ test tube-full of 6 M nitric acid. Rinse a third time with distilled water. Rinse your culture tubes with acetone, and then again with distilled water. Allow the test tubes to dry completely before beginning the activity.

Answers to Questions

1. What is the product of the reaction?
   Metallic silver.
2. Did the silver ions gain or lose electrons in the reduction process?
   The silver ions gained electrons in the reduction.
3. An oxidation reaction must take place along with a reduction reaction. Dextrose (a sugar) is the reducing agent for the reaction of silver ions in this experiment. What happened to the sugar molecules?
   The dextrose molecules are oxidized; lost electrons.

Discussion

Reactions

Formation of Tollens’ reagent:

2AgNO₃ + 2NaOH →Ag₂O + H₂O + 2NaNO₃
Ag₂O + 4NH₃ + H₂O →2Ag(NH₃)₂OH

Reduction of reagent:

References

Ehrenkranz, D.; Mauch, J. J. Chemistry in Microscale, Book I, Kendall/Hunt: Dubuque, IA, 1990.

Shakhashiri, B. Chemical Demonstrations: A Handbook for Teachers of Chemistry; University of Wisconsin: Madison, 1992; Vol. 4; pp 240.

Introduction

Make a silvered test tube using a classic analytical test for silver.

Concepts

• Oxidation–reduction
• Tollen’s test
• Electroless plating
• Reducing sugars

Background

Mirrors, or looking glasses, have been around since ancient times. The earliest mirrors were made by polishing disks of a metal such as bronze. These simple mirrors did not last very long due to oxidation of the metal by the atmosphere and abrasion of the metal from everyday use. Better mirrors were developed by backing glass with thin sheets of metal foil, usually silver. Those methods were used until a German chemist, Justus von Leibeg (1803–1873), first used the silvering process in 1835. This process, which plates the glass with a thin layer of silver atoms, is still used in the manufacture of the common household mirror.

Tollens’ test is similar to the silvering process and is used by chemists to determine if an aldehyde is present in a solution. Treatment of the aldehyde with a solution of silver nitrate in ammoniacal sodium hydroxide produces a thin layer of silver on a glass surface. This process does not require any electricity and is called electroless plating. Most household mirrors are made with silver because light reflected from a silvered mirror has a slight pink tinge to it, giving human skin a “better” color. In this experiment, silver metal is produced. Dextrose, a reducing sugar, is used to reduce silver ions to silver metal that will be deposited on the inside of a small culture tube.

Materials

Prelab Questions

Post-Lab Questions

1. What is the product of the reaction?
   
   
2. Did the silver ions gain or lose electrons in the reduction process?
   
   
3. An oxidation reaction must take place along with a reduction reaction. Dextrose (a sugar) is the reducing agent for the reaction of silver ions in this experiment. What happened to the sugar molecules?

Safety Precautions

Silver nitrate will stain skin and clothing. Avoid contact with eyes and skin. Ammonium nitrate solution is toxic by ingestion. It is a skin, eye and respiratory irritant. Sodium hydroxide solution is strongly corrosive. Avoid all contact with skin and eyes. 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.

Procedure

1. Fill a 400-mL beaker three-quarters full with water.
2. Obtain a culture tube and add the following amounts of solution to it in order:

1. 8 drops of 10% sodium hydroxide
2. 8 drops of 5% dextrose
3. 4 drops of 12% ammonium nitrate
4. 4 drops of 8% silver nitrate

3. Quickly place a square of Parafilm over the culture tube and shake it vigorously. Continue shaking the tube for about 3 minutes.
4. Pour any remaining solution in the culture tube into the beaker filled with water. This is a safety precaution to prevent the possible formation of an explosive nitrate mixture.
5. Rinse the mirrored culture tube thoroughly but gently with distilled water.
6. Allow the tube to air dry.
7. Consult your instructor for appropriate disposal procedures.

1. What is the product of the reaction?
2. Did the silver ions gain or lose electrons in the reduction process?
3. An oxidation reaction must take place along with a reduction reaction. Dextrose (a sugar) is the reducing agent for the reaction of silver ions in this experiment. What happened to the sugar molecules?