Final answer:
After repeated testing, if the solution contains a non-reducing sugar, there will be no reaction with Tollen's or Benedict's reagents as these sugars lack the necessary free aldehydic or ketonic group. For confirmation, non-reducing sugars may be hydrolyzed to their monomers, which might react positively if they are reducing sugars.
Step-by-step explanation:
When a solution contains a non-reducing sugar such as sucrose and the test is repeated after an initial negative result, no visible reaction will occur even if the test is with common reagents like Tollen's or Benedict's. These tests depend on the presence of free aldehydic or ketonic groups to reduce metal ions in the reagents, which non-reducing sugars lack. As a result, no silver mirror will be formed in the case of Tollen's test, and no red precipitate will be observed in the case of Benedict's test. Therefore, these tests are useful to differentiate between reducing and non-reducing sugars.
However, for confirmation, non-reducing sugars may be subjected to acid hydrolysis, which breaks them down into their monosaccharide components. These monomers can be reducing sugars, and if they are, they will react positively in these tests.
Non-reducing sugars are characterized by the lack of a free aldehydic or ketonic group, which is the functional group required for the reduction method used in many diagnostic tests. Sucrose, a common table sugar, is an example of a non-reducing sugar because its glycosidic linkage prevents the anomeric carbon from taking part in the open-chain form that exhibits reducing properties.