Hexoses, which are either aldoses or ketoses, show reducing properties. This reducing property is the basis of the test for sugar in the urine and in the blood. When reducing agent is treated with an oxidizing agent such as Cu
2+ complex ion,
+ a red-orange precipitate of copper(I) oxide (Cu
2O) is formed. The unbalanced equation for the reaction of an aldehyde with Copper (II) complex ion can be written as follow:
aldehyde + Cu2+ heat NAOH