A student performs a Benedict's test on a sample to detect the presence of reducing sugars. After heating, the solution changes from blue to brick-red. What does this result indicate?

• A. The test is positive for reducing sugars.
• B. The test is negative for reducing sugars.
• C. The test is inconclusive.
• D. The test is positive for non-reducing sugars.

Answer: (A)

Verified step by step guidance

1. Understand the purpose of Benedict's test: it is a chemical test used to detect the presence of reducing sugars in a sample. Reducing sugars have free aldehyde or ketone groups that can reduce the copper(II) ions in Benedict's reagent to copper(I) oxide.
2. Recall the color change associated with Benedict's test: the reagent starts as a blue solution due to copper(II) sulfate. When reducing sugars are present and the solution is heated, the copper(II) ions are reduced to copper(I) oxide, which precipitates as a brick-red solid.
3. Interpret the observed color change: a change from blue to brick-red indicates the formation of copper(I) oxide, which means the sample contains reducing sugars.
4. Contrast this with a negative result: if no reducing sugars are present, the solution remains blue because no reduction of copper(II) ions occurs.
5. Conclude that the observed brick-red precipitate confirms a positive Benedict's test for reducing sugars in the sample.