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I have read that tollens reagent is unstable and hence must be freshly prepared before testing. However my school has a bottle of 'tollens reagent' on the shelf for use in organic qualitative analysis and when i asked my teacher she said they don't need to replace it and it's a special bottle. (it has a brown tint) I have tested for aldehydes and gotten a fairly clear silver mirror with this solution so i am confused as to what is going on here.

  • Is this actually tollens reagent or just an AgNO3 solution? Or something else totally?

  • Can you get a clear silver mirror with just an AgNO3 solution?

  • Why exactly is tollens reagent unstable and is this magical bottle story feasible atleast temporarily?

Gaurav Sai Maddipati
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2 Answers2

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Tollens' reagent is sensitive and decomposed by violet and ultra-violet rays. If the bottle glass stops these rays, the reagent in such a bottle will resist decomposition. But it is not possible to obtain a nice silver mirror with just an $\ce{AgNO3}$ solution

Maurice
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Is this actually tollens reagent or just an AgNO3 solution? Or something else totally?

It is an aged bottle of Tollens reagent.

Can you get a clear silver mirror with just an AgNO3 solution?

If just silver nitrate is used (without ammonia) then the silver forms more quickly, as a suspension rather than coating on the surface of the glass. leading to a black and cloudy appearance. This is why ammonia is used to form the diamminesilver(I) ion before reaction with an aldehyde. This ion is harder to reduce than silver ions, resulting in a slower, more controlled production of silver during the reaction. (Source)

Why exactly is tollens reagent unstable and is this magical bottle story feasible atleast temporarily?

Tollens reagent is sensitive to light. Also, Tollens reagent is never stored but it is prepared in-situ due to the danger of forming silver nitride. See: Is Tollen's test safe?

Nilay Ghosh
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