Both Glucose and Sucrose give Fehling’s test:

• (A). True
• (B). False

The correct answer to your question is (A) True. Both glucose and sucrose can give a positive result in Fehling's test, but it's important to understand the context in which this occurs, especially since sucrose behaves differently than glucose in this test.

Understanding Fehling's Test

Fehling's test is a classic chemical test used to identify reducing sugars. It involves the reaction of a sugar with Fehling's solution, which contains copper(II) ions. When a reducing sugar is present, it reduces the copper(II) ions to copper(I) oxide, resulting in a characteristic brick-red precipitate.

Glucose: A Reducing Sugar

Glucose is a monosaccharide and a well-known reducing sugar. When glucose is mixed with Fehling's solution and heated, it readily donates electrons to the copper ions, leading to the formation of that brick-red precipitate. This is a clear indication that glucose is present.

Sucrose: The Disaccharide Dilemma

Sucrose, on the other hand, is a disaccharide composed of glucose and fructose. In its standard form, sucrose does not have a free aldehyde or ketone group, which are necessary for it to act as a reducing sugar. Therefore, sucrose does not give a positive result in Fehling's test when tested directly.

How Sucrose Can Still Yield a Positive Result

However, if sucrose is hydrolyzed (broken down) into its constituent monosaccharides, glucose and fructose, it can then participate in Fehling's test. This hydrolysis can occur in acidic conditions or through enzymatic action. Once hydrolyzed, the resulting glucose can reduce the copper ions, leading to a positive test result.

• Glucose: Directly reduces copper ions in Fehling's test.
• Sucrose: Does not reduce copper ions directly but can do so after hydrolysis.

Summary of Key Points

In summary, while glucose is a reducing sugar that gives a positive Fehling's test, sucrose does not do so in its intact form. However, upon hydrolysis, it can yield glucose, which will then react positively in the test. Thus, the statement that both glucose and sucrose give Fehling's test can be considered true under specific conditions.