Expt 075 -- Silver Mirror Reaction

A silver mirror typical of those found around the home is produced.

Safety

• Nitric acid and sodium hydroxide are corrosive and cause burns and blindness. Silver nitrate causes stains. Wear goggles and apron. Most of the chemicals used are toxic. Handle these chemicals with caution. Avoid ingesting the chemicals. Wash spills immediately with large amounts of water. Wash hands after the experiment. Methanol is flammable; avoid open flames. Know the location of the fire equipment; review use of that equipment before beginning work.
• Always mix the chemicals fresh and dispose of them immediately after use with large amounts of water. The chemicals may form explosive silver fulminate (Ag₂C₂N₂O₂) on standing; never premix the chemicals.
• Hold the tube inside a plastic bag while shaking.

Procedure

1. Clean the inside of a test tube provided for this experiment thoroughly. A clean test tube, free of any dirt or grease, is essential. Use a new test tube. If a used test tube is available instead, wash it with a test tube brush and some liquid dish washing detergent. Rinse thoroughly at the tap.
2. Whether starting with a new or freshly washed tube, rinse the test tube with, in order:
   1. distilled water
   2. 1 mL of 6 M nitric acid (discard in disposal jar)
   3. distilled water
   4. 1 mL methanol
   5. distilled water.

      !!!Click here to See Picture.

3. Add the following solutions in the order shown:
   1. 8 drops stabilized honey solution (5%). Wet the sides of the tube as the drops are added. Roll the tube to wet it with this solution.

      !!!Click here to See Movie.

   2. 4 drops 8.0% silver nitrate solution.
   3. 4 drops 12% ammonium nitrate solution.
   4. 8 drops 10% sodium hydroxide solution.

      !!!Click here to See Movie.

4. Quickly stopper the test tube, place it in a zipper-locking plastic bag, and shake vigorously. The inside surface of the test tube should be wetted for a good mirror to form. The mirror begins to form within the first minute. Continue shaking the test tube for about 3 minutes.

   !!!Click here to See Movie.

5. Observe the changes in appearance for 5 minutes.
6. Follow the disposal procedure recommended by the teacher. Either wash the solution down the drain with 1 liter of water, or add the mixture to a disposal jar. Handling this material properly is important; this solution can form an explosive mixture (after standing many hours or days).
7. Rinse the mirrored test tube gently but thoroughly with distilled water. Allow the tube to air dry.

   !!!Click here to See Picture.

   !!!Click here to See Picture.

8. Wash hands thoroughly.

Questions

1. Identify the visible reaction product; indicate whether this material was oxidized or reduced.
2. Every oxidation is accompanied by a reduction and vice versa. Identify the reaction partner of the product identified in question 1.
3. Identify alternatives to using honey in this procedure.

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

SmallScale 075 Silver Mirror Reaction

Watch the movies.

Carefully describe the reaction.

Answer the questions.

Curriculum-

Use when discussing oxidation reduction, organic chemistry, metals, or practical applications.

Safety-

• Nitric acid and sodium hydroxide are corrosive and cause burns and blindness. Silver nitrate causes stains. Wear goggles and apron. Most of the chemicals used are toxic. Handle these chemicals with caution. Avoid ingesting the chemicals. Wash spills immediately with large amounts of water. Wash hands after the experiment. Methanol is flammable; avoid open flames. Know the location of the fire equipment; review use of that equipment before beginning work.
• Always mix the chemicals fresh and dispose of them immediately after use with large amounts of water. The chemicals may form explosive silver fulminate (Ag₂C₂N₂O₂) on standing; never premix the chemicals.
• Hold the tube inside a closed plastic bag while shaking.

Time-

Teacher Preparation: 20 minutes

Class Time: 30 minutes

Materials-

• 13- x 100-mm test tubes; cork to fit
• 5 % honey (5 g honey in 50 mL water. Add 0.6 g tartaric acid, boil, then cool the solution. Add 10 mL ethanol and dilute to 100 mL.)
• 4.0 g silver nitrate in 50 mL water.
• 6.0 g ammonium nitrate in 50 mL water.
• 5 g sodium hydroxide in 50 mL water.
• 6 M nitric acid (Add 19 mL concentrated nitric acid to 20 mL of distilled water, and add enough distilled water to bring the total volume to 50 mL.)
• methanol

Disposal-

• Basic solutions of silver ammine form explosive substances upon standing. Collect the reaction mixtures in a second beaker (jar).
• Some teachers permit students to keep silvered tubes as souvenirs of the course. Carefully wash the tubes with distilled water.
• The teacher working in a hood with an apron and goggles should carefully conduct the following disposal procedures.
• To recover the silver from the mirrors dissolve the silver mirrors in a minimal amount of concentrated nitric acid. Collect the HNO₃ rinsing solutions in one disposal beaker (jar). Carefully dilute the HNO₃ waste by pouring it into 3 volumes of water. Use this solution in the next step.

  !!!Click here to See Movie.

• Pour the waste reaction mixture into diluted HNO₃ slowly, with stirring. When complete, check to be certain that the mixture is acidic. If not, add 6 M HNO₃ dropwise, with stirring, until acidic. Follow the silver recovery procedure described in the current Flinn Scientific Catalog to recover the silver.

Lab Hints-

• The methanol rinsing procedure improves the quality of the mirror formed.
• To coat a small portion of the test tube instead of the entire tube, use: 2 drops stabilized honey solution; 1 drop 8.0% silver nitrate solution; 1 drop 12% ammonium nitrate solution; and 2 drops 10% sodium hydroxide solution.

Background-

• Formations of the reagent (Tollen's Reagent):

  2 AgNO₃ + 2 NaOH --> Ag₂O + H₂O + 2 NaNO₃

  Ag₂O + 4 NH₃ + H₂O --> 2 Ag(NH₃)₂OH (Tollen's reagent)

• Reduction of the reagent:

  RCHO + 2 Ag(NH₃)₂OH --> RCOO(NH₄) + 2 Ag + 3 NH₃ + H₂O

  (R represents a group of atoms; in the simplest case, R = H when the reducing agent is formaldehyde.)

Answers-

Q1. Identify the visible reaction product; indicate whether this material was oxidized or reduced.

A1. Silver metal was reduced from Ag⁺ in the reaction.

Q2. Every oxidation is accompanied by a reduction and vice versa. Identify the reaction partner of the product identified in question 1.

A2. A sugar in the honey was oxidized.

Q3. Identify alternatives to using honey in this procedure.

A3. Many reducing agents can replace honey in this procedure. The reaction must be slow enough to permit formation of a mirror.

Reference-

Kemp, M. Journal of Chemical Education 1981,58, 655. An early version of this experiment was developed by Fen Lewis, Wadsworth, OH at the 1987 Dreyfus Woodrow Wilson summer program.

Key Words 1-

oxidation, reduction, redox, mirror, Tollen's reagent,

Elements-

Ag C