Question

What is Fehling’s solution?

Answer 1

To answer this question, we first need to understand what are solutions. In chemistry, a solution is a homogeneous mixture of two or more compounds in relative proportions that can be changed continuously up to the solubility limit. The term "solution" is most frequently associated with the liquid state of matter; however, gases and solids can also form solutions.

Complete answer:
Fehling’s solution - Fehling's solution is a chemical reagent that can be used to distinguish between water-soluble carbohydrate and ketone functional groups, as well as a test for reducing and non-reducing sugars, in addition to the Tollens' reagent test. Hermann von Fehling, a German scientist, invented the test in 1849.
Fehling's solution is generated by combining two different solutions: Fehling's A, a deep blue aqueous copper (II) sulphate solution, and Fehling's B, a colorless aqueous potassium sodium tartrate (also known as Rochelle salt) solution made strongly alkali with sodium hydroxide.
Because the copper (II) complex created by their combination is not stable: it slowly decomposes into copper hydroxide in alkaline circumstances, these two solutions, which are stable individually, are joined when needed for the test. The active reagent is a Cu2+ bis(tartrate) complex that acts as an oxidizer. Bidentate alkoxide ligands are tartrate tetra anions.
So, we conclude that Fehling's solution is a copper (II) sulphate alkaline solution containing sodium potassium tartrate (Rochelle salt).

Note :
To discriminate between aldehyde and ketone functional groups, Fehling's solution is used. Aldehydes oxidize to produce a positive result, but ketones (save for -hydroxy ketones) do not. A general test for determining monosaccharides and other reducing sugars is Fehling's test. It shows a positive test result for aldose monosaccharides, which is mostly due to the oxidizable aldehyde group.