Verification of reducing sugar with Fehling's solution

Chemicals needed

Fehling's solution    C    R 35    S (2)-26-27-37/39

glucose

Equipment needed

test tube
burner (preferably alcohol)

Test procedure

• Add a spatula-tipful glucose to a test tube and dissolve in approx. 3 ml water.
• Add a couple of drops of Felhling's solution.
• Heat with the burner. After a certain amount of time a yellow turbidity rather suddenly develops.

Disposal

• The reaction solution can be discharged into the drainage.

Elucidation

Fehling's solution is alkaline and contains Cu(II). This does not precipitate inasmuch as it is complexed with tartrate. The aldehyde group of glucose is oxidized to carboxylic acid, whereby Cu(II) is reduced to Cu(I). This is precipitated as copper(I)-hydroxide. In general, one can verify with Fehling's solution reducing compounds, especially aldehyde.

Photos

Reduction of Fehling's solution with glucose

Literature

based on a school experiment