The chemical composition of Fehling's reagent varies slightly depending on its preparation method. However, it typically consists of two separate solutions that are mixed together before use:

Fehling's Solution A:

- Copper sulfate pentahydrate (CuSO4*5H2O): This is the source of copper ions, which are essential for the reaction to occur.

Fehling's Solution B:

- Potassium hydroxide (KOH): Provides the alkaline conditions necessary for the reaction.

- Potassium sodium tartrate (KNaC4H4O6*4H2O or Rochelle salt): This compound helps to dissolve and maintain the copper ions in the solution.

When equal volumes of Fehling's Solution A and Solution B are mixed, a deep blue solution forms. This solution contains the copper ions complexed with tartrate ions, which makes them more stable and reactive.

Note: The actual concentration of these components may vary depending on the specific protocol or manufacturer of the Fehling's reagent.