Question:
Which of following observations is found in Tollens test for aldehydes?
Which of following observations is found in Tollens test for aldehydes?
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Tollens reagent deposits a silver mirror with aldehydes on warming.
Updated On: Oct 1, 2026
- The formation of pink or magenta color upon the addition of the reagent to the sample solution.
- Formation of an Ag layer on sides of test tube upon addition and warming of the reagent.
- Formation of brick-red precipitate upon heating with reagent.
- Appearance of red color upon shaking with reagent.
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
Tollens reagent is ammoniacal silver nitrate, \([\text{Ag(NH}_3)_2]^+\). Aldehydes are oxidised by it and silver ions are reduced to metallic silver.
Step 2: Detailed Explanation:
\[ \text{RCHO} + 2[\text{Ag(NH}_3)_2]^+ + 3\text{OH}^- \rightarrow \text{RCOO}^- + 2\text{Ag} + 4\text{NH}_3 + 2\text{H}_2\text{O} \]
The silver deposits as a shining layer (silver mirror) on the wall of the test tube on gentle warming.
A pink or magenta colour is seen in Schiff's test. A brick-red precipitate is seen in Fehling's test.
Step 3: Final Answer:
A silver mirror, option (B).
Final Answer:
Tollens test gives a silver mirror. \[ \boxed{\text{(B) }\text{Ag layer on the test tube}} \]
Tollens reagent is ammoniacal silver nitrate, \([\text{Ag(NH}_3)_2]^+\). Aldehydes are oxidised by it and silver ions are reduced to metallic silver.
Step 2: Detailed Explanation:
\[ \text{RCHO} + 2[\text{Ag(NH}_3)_2]^+ + 3\text{OH}^- \rightarrow \text{RCOO}^- + 2\text{Ag} + 4\text{NH}_3 + 2\text{H}_2\text{O} \]
The silver deposits as a shining layer (silver mirror) on the wall of the test tube on gentle warming.
A pink or magenta colour is seen in Schiff's test. A brick-red precipitate is seen in Fehling's test.
Step 3: Final Answer:
A silver mirror, option (B).
Final Answer:
Tollens test gives a silver mirror. \[ \boxed{\text{(B) }\text{Ag layer on the test tube}} \]
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