I'm pretty sure tollens doesnt react with alcohols (at least thats what the spec says).
That being said, it is an oxidising reagent, and it probably can give a false positive if reacted with a primary alcohol (as they are quite easy to oxidise) - as this would then form an aldehyde, and give a positive result. Not sure about the conditions, but someone on chem stack exchange said he got a false positive upon heating.
That being said, it is an oxidising reagent, and it probably can give a false positive if reacted with a primary alcohol (as they are quite easy to oxidise) - as this would then form an aldehyde, and give a positive result. Not sure about the conditions, but someone on chem stack exchange said he got a false positive upon heating.
Original post by FM1/FP1
so I just did an exam question which basically stated that you can use tollens reagent to tell apart an aldehyde from an alcohol, but from my knowledge this is incorrect since both aldehydes and alcohols will form a silver mirror right?
Alcohols do not react with Tollens’ reagent, as it is a selective oxidising agent that is capable of oxidising aldehyde groups, but not hydroxyl groups.
You may get a false positive with some heating though if the alcohol is primary, as there may be some degree of atmospheric oxidation that has led to the formation of an aldehyde.
Original post by felix k
i have added tollens reagent to a primary alcohol and produced a positive result
Hello felix k!
I disagree with your statement.😉
Tollen's reagent, which contains silver nitrate and ammonia, reacts with aldehydes to form a silver mirror on the surface of the test tube. Not all aldehydes will react with Tollen's reagent and other analytical conditions may be required. Chemists use Tollen's reagent as a useful means of identifying aldehydes, but they must use it with other confirmatory tests.
Alcohols will not react with this reagent.
I suggest a simple memo to help you remember the difference:
•
Aldehydes react with Tollen's reagent to form a silver mirror.
•
Alcohols do not react with Tollen's reagent.
Original post by felix k
i have added tollens reagent to a primary alcohol and produced a positive result
It’s not impossible- it means the sample of the alcohol is old and some of it has oxidised to an aldehyde (remember that oxygen in the air is an oxidising agent).
It’s the aldehyde formed that has reacted - not the alcohol.
(edited 5 months ago)
Original post by Nitrotoluene
Hello felix k!
I disagree with your statement.😉
Tollen's reagent, which contains silver nitrate and ammonia, reacts with aldehydes to form a silver mirror on the surface of the test tube. Not all aldehydes will react with Tollen's reagent and other analytical conditions may be required. Chemists use Tollen's reagent as a useful means of identifying aldehydes, but they must use it with other confirmatory tests.
Alcohols will not react with this reagent.
I suggest a simple memo to help you remember the difference:
Sandro
I disagree with your statement.😉
Tollen's reagent, which contains silver nitrate and ammonia, reacts with aldehydes to form a silver mirror on the surface of the test tube. Not all aldehydes will react with Tollen's reagent and other analytical conditions may be required. Chemists use Tollen's reagent as a useful means of identifying aldehydes, but they must use it with other confirmatory tests.
Alcohols will not react with this reagent.
I suggest a simple memo to help you remember the difference:
•
Aldehydes react with Tollen's reagent to form a silver mirror.
•
Alcohols do not react with Tollen's reagent.
You are correct that alcohols don’t react with Tollen’s reagent and that (most) aldehydes react with it, but I think you misread the post.
Felix k stated that they had done an experiment wherein they tested what was supposed to be a 1° alcohol using Tollen’s reagent, but they got a positive result and were confused. See my post above for an explanation as to what caused them to get a positive test.
Original post by TypicalNerd
You are correct that alcohols don’t react with Tollen’s reagent and that (most) aldehydes react with it, but I think you misread the post.
Felix k stated that they had done an experiment wherein they tested what was supposed to be a 1° alcohol using Tollen’s reagent, but they got a positive result and were confused. See my post above for an explanation as to what caused them to get a positive test.
Felix k stated that they had done an experiment wherein they tested what was supposed to be a 1° alcohol using Tollen’s reagent, but they got a positive result and were confused. See my post above for an explanation as to what caused them to get a positive test.
Hello TypicalNerd!
You are right.
I didn't check the first and second posts thoroughly. Yes, an alcohol can oxidise to aldehyde when exposed to atmospheric oxygen and can age in the bottle, which can give a false positive with Tollens' reagent.
However, I have written a summary of Tollens' reagent. It may be helpful to other users, thanks for your input.
Sandro
Original post by Pigster
Is ethenol considered a primary alcohol? That'd give a silver mirror.
(I'll get the OP wasn't given ethenol, though - that'd just be cruel).
(I'll get the OP wasn't given ethenol, though - that'd just be cruel).
I’m pretty sure it isn’t- I don’t think enols that tautomerise to carbonyls are classified as 1°, 2° or 3°.
How would this be made using Isopropyl Alcohol
www.youtube.com/shorts/_EbL18f-VdI
www.youtube.com/shorts/_EbL18f-VdI
Original post by c8rsa
How would this be made using Isopropyl Alcohol
www.youtube.com/shorts/_EbL18f-VdI
www.youtube.com/shorts/_EbL18f-VdI
That isn’t Tollen’s test - that’s just exploiting the fact that the paint is soluble in isopropanol to some extent and therefore any excess washes off.
You could alternatively plate it with metallic silver either electrochemically or by Tollens’ test, but isopropanol would be utterly useless for both of these procedures.
Original post by TypicalNerd
That isn’t Tollen’s test - that’s just exploiting the fact that the paint is soluble in isopropanol to some extent and therefore any excess washes off.
You could alternatively plate it with metallic silver either electrochemically or by Tollens’ test, but isopropanol would be utterly useless for both of these procedures.
You could alternatively plate it with metallic silver either electrochemically or by Tollens’ test, but isopropanol would be utterly useless for both of these procedures.
Any ideas as to which chemicals could be used for this displacement of silver? I presume it uses nanoparticles, a polymer to hold in place and IPA.
Sorry for hijacking thread, couldn't find anything else regarding silver finishes on website
Original post by c8rsa
Any ideas as to which chemicals could be used for this displacement of silver? I presume it uses nanoparticles, a polymer to hold in place and IPA.
Sorry for hijacking thread, couldn't find anything else regarding silver finishes on website
Sorry for hijacking thread, couldn't find anything else regarding silver finishes on website
The paint used in the YouTube short probably isn’t silver nanoparticle based - chrome formulations apparently do contain finely divided metal but an article I found suggested the metal of choice is actually aluminium (which makes sense because it is cheaper, nowhere near as toxic and much less susceptible to tarnishing).
https://www.pcimag.com/articles/98311-finding-chrome-formulations-puzzling
If you wanted to coat it in metallic silver, I’d personally use glucose as the reducing agent since it’s common and reduces Tollens’ reagent to silver metal. Immerse the items you wish to plate in silver in a mix of glucose solution and Tollen’s reagent (which is prepared by first adding sodium hydroxide to a solution of silver nitrate, followed by enough concentrated ammonia for all the solids formed in the solution to re-dissolve). IPA is useless for this, because it isn’t an aldehyde and does not readily tautomerise to one, so it cannot reduce Tollen’s reagent. You also don’t need an adhesive for the silver layer to stick to the item in question.
Original post by TypicalNerd
The paint used in the YouTube short probably isn’t silver nanoparticle based - chrome formulations apparently do contain finely divided metal but an article I found suggested the metal of choice is actually aluminium (which makes sense because it is cheaper, nowhere near as toxic and much less susceptible to tarnishing).
https://www.pcimag.com/articles/98311-finding-chrome-formulations-puzzling
If you wanted to coat it in metallic silver, I’d personally use glucose as the reducing agent since it’s common and reduces Tollens’ reagent to silver metal. Immerse the items you wish to plate in silver in a mix of glucose solution and Tollen’s reagent (which is prepared by first adding sodium hydroxide to a solution of silver nitrate, followed by enough concentrated ammonia for all the solids formed in the solution to re-dissolve). IPA is useless for this, because it isn’t an aldehyde and does not readily tautomerise to one, so it cannot reduce Tollen’s reagent. You also don’t need an adhesive for the silver layer to stick to the item in question.
https://www.pcimag.com/articles/98311-finding-chrome-formulations-puzzling
If you wanted to coat it in metallic silver, I’d personally use glucose as the reducing agent since it’s common and reduces Tollens’ reagent to silver metal. Immerse the items you wish to plate in silver in a mix of glucose solution and Tollen’s reagent (which is prepared by first adding sodium hydroxide to a solution of silver nitrate, followed by enough concentrated ammonia for all the solids formed in the solution to re-dissolve). IPA is useless for this, because it isn’t an aldehyde and does not readily tautomerise to one, so it cannot reduce Tollen’s reagent. You also don’t need an adhesive for the silver layer to stick to the item in question.
Would glucose make this safer to store as left over Tollens has to be disposed of after use?
Original post by c8rsa
Would glucose make this safer to store as left over Tollens has to be disposed of after use?
Leftover Tollens’ reagent has to be disposed of, irrespective of which aldehyde you use to reduce it. The [Ag(NH3)2]^+ complex isn’t too stable and decomposes to explosive silver nitride if left alone too long.
To be honest, all you really need to do is acidify the solution enough to decompose the [Ag(NH3)2]^+ complex (I’d recommend using HCl for this, as the silver ions would then precipitate, making it possible to filter put the silver and just pour the filtrate down the sink)
(edited 2 weeks ago)
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