The aldehydes in reducing sugars will reduce silver ion from Tollen's reagent to metallic silver, leaving a reflective mirror on the inside of a flask.


RCHO  +  2Ag(NH3)2OH  →  2Ag(s) + RCOONH4+  +  NH3  +   H2O

To Conduct Demonstration:  

  1. Add 5mL 10% AgNO3 to a florence flask.
  2. Add 1mL 10% NaOH.  NOTE:  The first two steps may be carried out immediately before lecture.
  3. Add 15M NH3 (ammonia)—about 10 drops—until the brownish silver oxide has just dissolved.  (The solution may still appear dark.)
  4. Add 7mL of 1% glucose (dextrose works best) solution and swirl for a few minutes.  A silver mirror will coat the inside of the flask. 

Safety and Disposal

Silver nitrate will stain skin and clothing on contact.  Gloves should be worn.  Avoid breathing ammonia vapors.

Use concentrated HNO3 to dissolve silver coating on flask. 


D.J. Pasto and C.R. Johnson, Laboratory Text for Organic Chemistry, p 409,1979.


Margaret Asirvatham, Spring 1988; Tom Cech, Fall 1995.