Question

Sucrose can be broken down into reducing sugars. Describe how you would test for the presence of reducing sugars.​

Answer 1

Answer:

Reducing sugar tests such as Benedict's and Fehling's test can be used to determine whether sugars are present in urine, which can be indicative of diabetes mellitus. They can also be used in a qualitative manner, such as in a titration experiment, to determine the amount of reducing sugars in a solution.

Fehling's Test

To carry out Fehling's test, the solution is diluted in water and warmed until fully dissolved. Next, Fehling's solution is added while stirring. If reducing sugars are present, the solution should begin to change colors as a rust or red colored precipitate forms. If reducing sugars are not present, the solution will remain blue or green.

How Fehling's Test Works

Fehling's solution is made by first making two sub-solutions. Solution A is made from copper(II) sulfate pentahydrate dissolved in water and solution B contains potassium sodium tartrate tetrahydrate (Rochelle salt) and sodium hydroxide in water. The two solutions are added together in equal parts to make the final test solution. The test is a detection method for monosaccharides, specifically aldoses and ketoses. These are detected when aldehyde oxidizes to acid and forms a cuprous oxide. Upon contact with an aldehyde group, it is reduced to cuprous ion, which forms the red precipitate and inedicates the presence of reducing sugars.

progress to green, yellow, orange, red and then a dark red or brown.

How Benedit's Test Works

Benedict's reagent is made from anhydrous sodium carbonate, sodium citrate and copper(II) sulfate pentahydrate. Once added to the test solution, reducing sugars reduce the blue copper sulphate from the Benedict's solution to a red brown copper sulphide, which is seen as the precipitate and is responsible for the color change. Non-reducing sugars cannot do this. This particular test only provides a qualitative understanding of the presence of reducing sugars.