chemistry of christmas ornaments

Ok, here’s something for the holidays.

How to silver a glass Christmas ornament!

silver ornament

Materials:

  • distilled water
  • 5 ml acetone
  • 2.5 ml 0.5 M silver nitrate solution (AgNO3)
  • 2.5 ml 1.5 M ammonium nitrate solution (NH4NO3)
  • 5 ml 5% dextrose solution (C6H12O6)
  • 5 ml 10% sodium hydroxide solution (NaOH)
  • clear glass ornament (2-5/8″) – even a round-bottom flask will do!

Procedure:

  1. Rinse the inside of the ornament with acetone.
  2. Pour 2.5 mL the silver nitrate solution into a small beaker and set aside.
  3. Add 2.5 mL ammonium nitrate solution to the beaker of silver nitrate solution. Mix solutions by swirling the beaker or stirring.
  4. Pour 5 mL of dextrose solution into the glass ornament.
  5. Pour the silver nitrate and ammonium nitrate solution into the glass ball, followed immediately by the addition of 5 mL of the sodium hydroxide solution.
  6. Seal the top of the glass ornament and shake/stir vigorously. First, the silver will form large particles, and the solution will look an icky black-brown. Eventually, you will see a silver mirror coating form on the interior walls of the ornament.
  7. When the coating is satisfactory, pour out the solution in the ornament and rinse the inside with distilled water, followed by acetone.

IMPORTANT NOTE: Liquid waste should be rinsed with water to prevent formation of potentially explosive compound, silver nitride.

The reaction occurring in the demonstration is

CH2OH(CHOH)4CHO + 2 [Ag(NH3)2]+ + 3 OH  →  2 Ag  + CH2OH(CHOH)4COO  + 4 NH3 + 2 H2O

(dextrose)      +      (silver nitride)   +    (hydroxide)    →    (silver)    +  (oxidized dextrose)   +  (ammonia)  + (water)

Because dextrose has an aldehyde group (-CHO), it is capable of reducing silver nitride [Ag(NH3)2]+ in basic solution to metallic silver.  Remember the Tollens test for aldehydes in Ochem? This is exactly it, expect now we are using the silver precipitated in the reaction to plate the inside of our reaction vessel! This plating occurs without the application of an electrochemical circuit, and so we call this coating technique “electroless plating”.

I found this demonstration in a video by Prof. Chris Bishop at https://www.youtube.com/watch?v=ti_E2ZKZpC4. See 12:17!

(in the video, Prof. Bishop uses glucose instead of dextrose, and this works too because glucose has an aldehyde group – and will register “positive” on the Tollens test, forming metallic silver!)

Materials list obtained from http://chemistry.about.com/od/christmaschemistry/a/Silver-Ornaments.htm

Procedure adapted from the site above and from http://cldfacility.rutgers.edu/content/formation-silver-mirror-glass-surface

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