Chemistry: tests for functional groups?

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Chicken
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#21
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#21
(Original post by Chicken)
Right well I've looked all through my text books (which are uni not A-Level) ones, and they don't have any distinguishing tests in them whatsoever. So I'm afraid i can't help anymore (not that I helped to begin with!), the only thing is to keep on trying interent searches. Sorry!!!
Actually, you could try oxidising the alcohols, as primary and secondary alcohols oxidise to different things. And with ester and carboxylic acids, you coulud hydrolyse, as an ester will hydrolyse and a carboxylic acid won't. But these aren't really simple tests really, I don't know how complicated you want to go.
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jediknight007
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#22
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(Original post by Chicken)
Actually, you could try oxidising the alcohols, as primary and secondary alcohols oxidise to different things. And with ester and carboxylic acids, you coulud hydrolyse, as an ester will hydrolyse and a carboxylic acid won't. But these aren't really simple tests really, I don't know how complicated you want to go.
I see. You see the point where I have either an alcohol, carboxylic acid, ester or phenol? I would use Potassium Dichromate to test for the alcohols right? If it is an alchohol, I could oxidise it and it would be either an aldehyde (from a primary alcohol) or a ketone (from secondary alcohol), I could then just use the 2,4DNP to distinguish between the 2! If it's positive, it would be an aldehyde and therefore, a primary alcohol. If it's negative, it would be an ketone and therefore, a secondary alcohol. I'm pretty sure this would work. What do you think? It would mean I have to use 2,4DNP twice though since I would have used it in the first place to distinguish between a carbonyl and a non-carbonyl. Do they allow this?

With the carboxylic acid and ester, I could hydrolyse it but what would be formed?
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jediknight007
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#23
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#23
Hi, I have just got some feedback and it looks like I have forgotten about the tertiary alcohols! It doesn't oxidise when Potassium Dichromate is added so therefore, I'm still left with esters, tertiary alcohols, phenols and carboxylic acids! I'm ok with the phenol and my teacher also said that esters are quite boring because they don't decolourise in Bromine Water and don't oxidise. Therefore, should I leave my ester last since that is negative in most of my tests?

I probably didn't get enough help yesterday since it was a Sunday and yea, I hate Sundays too! If anyone here has done this coursework or is doing it and is in the mood to help me out, please do! The deadline has been extended to another week to the 17th because it looked like no-one had done anything over the half-term so I guess I'm really lucky!
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Unregistered
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#24
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#24
Hi, I'm also doing the same piece of coursework. I got a D in my AS Chemistry and I can't seem to remember all of the tests for the different functional groups! The only one that I can seem to remember is the Bromine Water one for Alkenes.
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Unregistered
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#25
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#25
Carboxylic acid is acidic, ester is not.

Litmus paper test maybe?
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jediknight007
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#26
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#26
(Original post by Unregistered)
Carboxylic acid is acidic, ester is not.

Litmus paper test maybe?
Yea, a friend of mine told me about that today as well. It's carboxylic ACID so durhhhhh!!!! You see how dumb I am at Chemistry?

However, don't phenols also turn red with Litmus blue? How would you be able to distingush between phenols and carboxylic acids then? My friend suggested testing for the benzene ring since only phenol has it and carboxylic acids don't.
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jediknight007
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#27
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Hi, a friend of mine told me that Phenols also decolourise bromine water via electrophilic substitution and that it's possible that Carboyxlic acids also decolourise to produce Carbonayl bromide. Is this true? I'm really stuck now!

Btw, I got my Implementing back yesterday and I didn't get a mark! I would have got a 7 (highest) but my observations were crap and since the marking scheme is hierarchial (which I think is stupid), I must have failed and got a 0! I have another chance to do the Implementing next time but if I do crap on that one as well, my teacher says she will just allow me to add in some observations to the current one and I'll get the 7. God, I hate Chemistry coursework! I seem to get high marks in Psychology and Biology coursework (A grades) but I do so crap in my Chemistry!
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Broken_Link
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#28
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#28
assuming there are many other A2 bums like me, on the verge of starting there chem organic unknown coursework

lets get one thing clear, If u read the spec again Jed dude, it says u dont have to test for 2ndry alcohols muhahahah

I more or less know what im doing, but if anyone has a completes flowcahrt I would like to see it.

and dont forget the bit about consulting more than 2 sources, just ramm it with information, thats what im going to do, not like my teacher will penalise me.
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rosa kakerlaken
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#29
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#29
i've got this weekend to do this piece of coursework and my teacher says that shes not allowed to help at all... so i'm a bit stuck... wat does phenol react with? na? K2Cr2O7? i think it reacts with sodium but not sure bout dichromate... my flowchart seems really short as well... quite worrying really... and i don;t know wat to do for the method... help!!!
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Broken_Link
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#30
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#30
PANIC!!!!!
heheh just kidding dont panic.
Phenol can react with bromine water to give a white precipitate, forgot what that is exactly, but i can let u know if u want.
my chart contained 6 different tests, 2,4DNP, tollens silver mirror, phosphorus(V) chloride, posstassium dichromate (oxiding agent), bromine water, and methyl red.
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karen_uk
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#31
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#31
which exam board are u with? im with AQA chemistry the coursework is really easy on the AQA board
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smile_missfitz
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#32
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#32
(Original post by Chicken)
Right well I've looked all through my text books (which are uni not A-Level) ones, and they don't have any distinguishing tests in them whatsoever. So I'm afraid i can't help anymore (not that I helped to begin with!), the only thing is to keep on trying interent searches. Sorry!!!
Hey, just thought you might want to know, the test for a carboxylic acid is to add a metal carbonate. if it gives off carbon dioxide then its a carboxylic acid - the carbon dioxide can be identified using limewater, i can't remember the details on how though! is that any help?

am =)
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Emsccasey
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#33
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#33
Started my flow diagram have been told to use as many tests as possible so suggest u use bromine water to confirm and litmus + oxidise suspected CooH to esters then test using litmus, put acid in water and dectect smell as discussed earlier.

Good luck with it, Don't forget to do ur safety assessments!!!!!!!
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Emsccasey
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#34
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#34
(Original post by Unregistered)
Hi, I'm also doing the same piece of coursework. I got a D in my AS Chemistry and I can't seem to remember all of the tests for the different functional groups! The only one that I can seem to remember is the Bromine Water one for Alkenes.
Sounds like u r coming from the same space as me, I got an E at as but have worked mega hard.

PCl5 (phosphorus pentacloride) can b used to test for (-OH) group, present in Alcohol, carboxylic acid, phenol.

Leaving u wth ester, aldehyde and ketone to distinguish between,
U must have heard of AgNO3 (amonical silver nitrate solution) distingishes between aldehyde + Ketone no silver mirror is formed wth Ketone.
24 dintirophenylhydrazine reacts with aldehyde and Ketone and a hydrazone is formed an orange ppt
so by process of elimintation phenol
Test for phenol, is acidic+ it decolurises bromine water white ppt formed
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