Fehlings Solution No.2 Clear ; 2.5L ChemSupply
ACR 0462-2.5L

Fehlings solution is named either A & B or 1 & 2. No1 (or A) is a bright blue solution of copper sulfate and No.2 (or B) is a colourless solution of potassium sodium tartrate (Rochelle salt). In organic chemistry, Fehling's solution is a chemical reagent used to differentiate between water-soluble carbohydrate and ketone (>C=O) functional groups, and as a test for reducing sugars and non-reducing sugars

Fehling's Solution 2 (B) is a clear, colorless, and strongly alkaline liquid consisting of potassium sodium tartrate (Rochelle salt) and sodium hydroxide.

It acts as a stabilizer and base when mixed with Fehling's Solution 1 (A), preventing the copper ions from precipitating before they react with reducing sugars or aldehydes.

When Fehling's Solution 2(B) is combined in equal volumes with Fehling's Solution 1 (A), the active reagent is formed. The active reagent is a tartrate complex of Cu²⁺, which serves as an oxidizing agent. . The mixture goes a deeper blue than the copper(II) sulfate. When heated with a reducing agent (like aldehydes or reducing sugars), the copper(II) complex oxidizes the compound and is itself reduced to copper(I) oxide, forming a distinct brick-red precipitate. Ketones are none reducing and give no red precipitate.