Fehling's A: This solution contains copper(II) sulfate (CuSO₄) dissolved in water.
Fehling's B: This solution contains a mixture of sodium potassium tartrate (also known as Rochelle salt - NaKC₄H₄O₆) and a strong base, usually sodium hydroxide (NaOH), dissolved in water.
How they work together:
When Fehling's A and Fehling's B are combined, the following reaction occurs:
* The tartrate ions in Fehling's B complex with copper(II) ions from Fehling's A, forming a deep blue solution of bis(tartrato)cuprate(II) complex. This complex is the actual reagent that reacts with reducing sugars.
Key point: There is no single chemical formula for Fehling's reagent because it's a mixture of two solutions that interact to form the active complex.
