Fehling’s test is a chemical test used to detect the presence of reducing sugars, particularly aldoses such as glucose and fructose. It is named after its developer, Hermann von Fehling, a German chemist who introduced the test in the 19th century.
The Fehling’s test involves the reaction of a reducing sugar with Fehling’s solution, which is a mixture of two separate solutions: Fehling’s A (copper(II) sulfate dissolved in water) and Fehling’s B (sodium potassium tartrate and sodium hydroxide dissolved in water). The two solutions are typically mixed in equal volumes before use.
When a reducing sugar is present, such as glucose or fructose, it reacts with the copper(II) ions in Fehling’s solution, reducing them to copper(I) oxide (Cu2O), which appears as a brick-red precipitate. The reaction can be summarized as follows:
Reducing sugar + Cu2+ → Reducing sugar-Cu2O (brick-red precipitate)
The Fehling’s test is commonly used in laboratory settings to identify the presence of reducing sugars in various substances. It is often employed in the analysis of carbohydrates and is particularly useful in differentiating between reducing and non-reducing sugars. However, it’s worth noting that Fehling’s test is not specific to a particular sugar and can yield positive results with other reducing substances as well.
