Silver Mirror

Introduction

Oxidation-reduction reactions are involved in many chemical changes. The most familiar examples of this type of reaction involve metallic elements. When a car rusts, the metallic iron is oxidized to iron(III) oxide. In this experiment, a metal will be produced by reduction of one of its compounds by another chemical that is oxidized.

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1. Thoroughly clean the inside of a test tube given to you for this experiment. A scrupulously clean test tube is essential for the successful completion of this experiment.
2. Rinse the test tube with distilled water. Taking care to keep the acid off your skin, rinse again with a 1/4 test tube full of 6 M nitric acid, followed by a rinse with distilled water. Discard under hood.
3. Rinse again with acetone, then with distilled water.
4. Add the following amounts of solutions in exact order as listed below:
   1. 8 drops stabilized honey solution (5%).
   2. 4 drops 8.0% silver nitrate solution.
   3. 4 drops 12% ammonium nitrate solution.
   4. 8 drops 10% sodium hydroxide solution.
5. Quickly stopper the test tube with a cork and shake it vigorously. The inside surface of the test tube should be wetted for a good coating. Continue shaking the test tube for about 3 minutes. Observe the changes in appearance for 5 minutes.
6. Wash the solution down the drain with 1 liter of water. This is an important safety precaution to prevent the possible formation of an explosive mixture (after standing many hours or days). Rinse the mirrored test tube gently but thoroughly with distilled water. Allow the tube to air dry.

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1. What is the visible 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. Honey (actually the sugars in honey) is the partner for the reaction of silver ions in this experiment. What happened to the sugar molecules?

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• Nitric acid is corrosive and causes burns and blindness. Silver nitrate causes stains. Wear goggles and apron. Handle these chemicals with caution. Wash spills immediately with large amounts of water.
• Always mix the chemicals fresh and dispose of them immediately after use with large amounts of water. The chemicals may form explosive silver fulminate on standing. Never premix the chemicals.

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1. Metallic silver
2. Silver ions gained electrons in reduction.
3. Sugar molecules are oxidized.

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• 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

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• The acetone rinsing procedure will improve the quality of the mirror formed. Using brand new test tubes helps too.
• If you wish to have the students reduce silver without coating the whole test tube , use 2 drops each of honey and sodium hydroxide, 1 drop each of silver nitrate and ammonium nitrate.

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• 30 13 x 100 mm test tubes and corks to fit them.
• 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.
• 10 g sodium hydroxide in 100 mL water.
• 6 M nitric acid (Add 38 mL concentrated nitric acid to 40 mL of distilled water, and add enough distilled water to bring the total volume to 100 mL.)
• acetone
  

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The Woodrow Wilson microscale version of this lesson was developed by:
Fen Lewis
Strongsville High School
7701 Beach Rd.
Wadsworth, Ohio 44281

Based upon:
Kemp, Marwin, Journal of Chemical Education 58, 655 (l981).

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