please help me.. i've been searching for a chemistry text that explains about the reactions that occur between tollen's reagent and aldehyde functional group... but, i fail to find one... now, can you help me to answer these question:
- what are the reactions involved until silver mirror is produced?
- why does it only produce silver mirror with aldehyde?
Originally posted by aku_EnSeM at 20-4-2007 09:38
and one last question.... how to post a new thread anyway.... the methods are different from last year...
You just click NEW button,don't click POLL or ACTIVITY button
The diaminesilver(I) complex is an oxidizing agent, which is itself reduced to silver metal, which in a clean glass reaction vessel forms a "silver mirror". This feature is used as a test for aldehydes, which are oxidized to carboxylic acids.
Tollen adalah oxidation agen, jadi kalau dia bertindakbalas dengan bahan tertentu, dia sendiri akan mengalami perubahan, dalam kes ini dia sendiri akan mengalami " reduction"... aldeyhe adalah component yg mengandungi satu atom oxigen yang mempunyai awan electron tidak berikatan dengan atom lain dan mempunyai double bond..yang mudah di " oxide"...
okay. this is the best text that ive found within this 3 months.
Tollen's Reagents = ammoniacal silver nitrate....
Silver is reduced to atomic silver, which occurs as a 'mirror'. So then it oxidised the aldehyde group. This is an alkaline oxidisation, and the alkaline oxidisation is given by the ionisation of ammonia. So the responding carboxylate anion is produced.
But, i didn't use ammonia during my lab. these were my reagents:
ammonium nitrate
silver nitrate
aldehyde (glucose)
preservative
a basic solution (i 4got)
1) where did the ammonia come from? or is it no longer useful because there exist the ammonium ion? and, does the ammonium ion represents the basic condition? if so, what is the purpose of using a basic solution?
2) why is this reaction only occur for aldehyde, not alcohol, or any other reducing agent?
Tollens' reagent is usually ammoniacal silver nitrate, but can also be other things, as long as there is an aqueous diamminesilver(I) complex.
Diamminesilver(I), [Ag(NH3)2]+, the active species in Tollens' reagent. Ion Ammonia a.ka ammonium act as a ligand in transition metal complexes.
Laboratory Preparation
* To aqueous silver nitrate, add a drop of dilute sodium hydroxide. A brown precipitate of silver oxide will form.
* Add ammonia until the precipitate just dissolves.
* This is ammoniacal silver nitrate, [Ag(NH3)2]NO3 (aq).
2. Alcohol is more stable compared to aldehye or ketone because its have single bond carbon with oxygen. alcohol can react with strong acid and base (e.g HCl or KOH) at room temperature or the absence or active catalyst like Nickel, Platinium at appopriate temperature
oit. apa motif hg tanya pasai kimia kat tenet neh.
aku qasa lg bagoih kalau hg p tanya cikgu skolah hg. dia bleh explain one to one dgn hg. lg senang. mcm2 hg bleh tanya.
Originally posted by aku_EnSeM at 20-4-2007 09:37 AM
Hi guys...
please help me.. i've been searching for a chemistry text that explains about the reactions that occur between tollen's reagent and aldehyde functional group... but, i fail to find ...
Chemm.... chemmistry...........
I have no idea...... ask me about physics then I can answer you
Originally posted by aku_EnSeM at 11-5-2007 03:58 PM
tanye sket, hey... u don't have to know this. u r wasting ur time....
:@ :@ :@ :@
Saya teramat benci cikgu macam ini.........
saya kelas kelima...sebab saya tak ambil Bio. saya ambil acc + physics + kimia. kelas 1-4 adalah pure sains pernah tanya cikgu benda, dia cakap kau kelas kelima, ajar pun buang masa saya, saya ditampar cikgu kerana tanya apa itu pai (3.142....); tanya kenapa nombor itu. dia tak tau jawab dan naik marah lalu tampar saya. satu lagi, saya pergi kelas pertama cari kawan saya cikgu kata kau mari sini buat apa? murid kelas ini adalah future doctor dan lawyer.........
aku tau tollen ni nak bezakan aldehyde ngan alketon je ..
erm .. kalau aku tak silap .. tollen reagent tu adalah reagent yang ada silver nitrate kot .. dalam bentuk ion .. and bile dia bertindak dengan aldehyde .. ion silver tu akan menjadi pepejal .. so terhasil la pepejal silver .. dats y ko nampak cermin ..
hahaha
aku dah 2 bulan tinggal mende neh ..
Post time 20-4-2007 09:37 AM
变色卡
Author
Post time 20-4-2007 09:19 PM
.tp bukan cam nie,dier tuh berlagak sket....
