[sam1280893]

Hello, i am a student from Hong Kong. I am searching information about the chemistry experiment tomorrow. Somehow i can`t find any from my textbook(it seems to be out of the recent AL syllabus) nor the internet so please, i need you guys' help.

1.What structural feature of carbonyl compounds determines how the carbonyl compounds react with Tollen's reagent and Fehling's reagent?

2.For methanal, ethanal and propanone which will give a positive result in iodoform test?

3.For iodoform reaction, why sometimes sodium carbonate is used instead of sodium hydroxide?

Thanks so much for spending time on my post.

[Yggdrasil]

Much of the information that you need can be found on wikipedia.  For example, for question #1, look at the following articles:

http://en.wikipedia.org/wiki/Tollen%27s_reagent
http://en.wikipedia.org/wiki/Fehling%27s_reagent

If you need any more help after reading these articles, let us know.

[agrobert]

http://en.wikipedia.org/wiki/Haloform_reaction

[sam1280893]

Thanks for giving me the links.
I've tired to learn and find out the answers after reading the information from the links provided. Can you guys check if i got the right concept for no.1 and 3?

1a.Total numbers of H atoms present on the carbonyl carbon will determine the reaction between the carbonyl compounds and Tollen's reagent. The more the H atoms present, the higher the rate of reaction, vice versa.

1b.The presence of aldehyde group determines the reaction between the carbonyl compounds and Fehling's reagent. The presence of aldehyde group is responsible for reducing the cupric ion from Fehling's solution. Therefore, there is not reaction between ketones and Fehling's reagent.

2. Only ethanal and propanone will give a positive result in iodoform test. It is because they contain the structure of -COCH3 which would react with OH- to form triiodoacetone.

3. For easier observation as CO2 will be produced.

However, my further question is how to explain why is Tollen's reagent able to test aliphatic and aromatic aldehydes but Fehling's reagent just for aliphatic aldehydes?