Define Tollens' reagent and Fehling's reagent. What is the key difference between them in distinguishing aldehydes from ketones? When would you use each reagent?

Tollens' reagent is a solution of silver nitrate in ammonia that oxidizes aldehydes to carboxylic acids, producing a silver mirror. Fehling's reagent is a mixture of copper(II) sulfate and alkaline tartrate that reduces aldehydes to form a red precipitate of copper(I) oxide. The key difference is that Tollens' reagent can only oxidize aldehydes, while Fehling's reagent can also oxidize aldehydes but is not effective for ketones. Tollens' reagent is typically used when a silver mirror test is desired, while Fehling's reagent is used for a color change test.

This question tests the student's understanding of two chemical reagents and their specific applications in organic chemistry. It requires the student to define both reagents, identify their key difference, and explain the context in which each is used, demonstrating a comprehensive understanding of their roles in distinguishing aldehydes from ketones.