NEED HELP :o im new :D

Hey all!!! ,

im new here n all :biggrin:

but im in a bit of trouble here :biggrin:

im doing A2 chemistry now (AS was a doddle) but the coursework has me a bit stumped :O

im not going to bother writing the question, im supposed to do the coursework :biggrin:

i just need a bit of help with a few reactions!

ill list em down, and feel free to tell me if i've got anything down incorrectly :biggrin:

cheers!!!

Alkene -> Addition of Bromine Water
Primary Alcohol -> Potassium Dichromate (orange -> green)
Tertiary Alcohol -> Pottasium Dichromate (No reaction at all)
Aldehyde -> 2,4 DNHP ----- Recrystallise and heat to find true nature
Or Tollen Reagent (coating tube in Silver Mirror)
Ketone -> 2,4 DNHP ----- Recrystallise and heat to find true nature
Carboxylic Acid -> Sodium Bicarbonate Test or Solubility Test (?)
Ester -> ??? not a clue!
Phenol -> Iron (III) Chloride making phenol bright purple!

its holidays at the moment, so i cant really double check with any one :/ seeing as there are only...2 PEOPLE in my class :biggrin:

anyway much appriciated :biggrin:

hope to see you all on the forum!

Reply 1

RyanY

Before I start I pressume you are asking about diagonstic test organic compounds? If so...
The ester as mentioned on another thread could be distinguished because of its charecteristic fruity odour. However, another way that may not be correct you'll have to check is to reverse the condensation reaction by hydrolysing the ester in the presence of an acid catalyst such as h2so4. You must use an excess of water since you want to drive the equilibrium right over to the reverse reaction. This will produce an alcohol and a carboxylic acid - to prove it was an ester that just undergone acid hydrolysis you could add universal indicator and it would turn red due from the presence of the acid. As I said I don't think there are any standard tests for an ester.

Reply 2

Demon_AS

Heemsj126

Hey all!!! ,

im new here n all :biggrin:

but im in a bit of trouble here :biggrin:

im doing A2 chemistry now (AS was a doddle) but the coursework has me a bit stumped :O

im not going to bother writing the question, im supposed to do the coursework :biggrin:

i just need a bit of help with a few reactions!

ill list em down, and feel free to tell me if i've got anything down incorrectly :biggrin:

anyway much appriciated :biggrin:

hope to see you all on the forum!

An easier test for aldehydes might be warming solution with Fehling's Reagent, which contains Cu2+ ions. Aldehydes reduce it to Cu+, which forms a brick red precipitate. Ketones don't oxidise, though, so you can use it to distinguish between the two.

Reply 3

Eau

2,4 DNHP ----- Recrystallise and heat to find true nature?

No idea what you mean there.

You usually add small amounts of ketone/aldehyde to approx. 3 cm^3 of Brady's reagent (2,4-dinitrophenylhydrazine in methanol and sulphuric acid). An orange/yellow precipitate should form.

Reply 4

HMR

Hi, I've got the same cwk as you and I must admit it stumped me too. Not finding the tests, but putting it in a flow diagram, which I presume you must do to. The tests you've got are fine. For an ester, it is fine to use smell. However, you may want to consider looking into its solubility in hot vs. cold alkali. Apparently esters will dissolve in hot alkali but not cold. Was told that by my old chem teacher but the test presumes that the unkown compound is a solid. Hope that helps.

Reply 5

Heemsj126

Thanks everyone! youve been a great help :biggrin:

im still stumped by the flow chart thing, like hayley! i dont get how they actually what me to do it :\, meh! ill have to try n see if something works out :/

and by the 2,4 dnhp recrystallise and heat, i mean heat the crystal, find the mp, and measure it to a chart of known organic compounds

(in the breifing paper, it says we have all standard equipment, apparatus, and chemicals available, so im assuming its either my text book, or atleast a chart!)

but i will take the fehling reagent into account!!

Reply 6

Demon_AS

Good stuff! I always found it easier to remember how Fehling's works, rather than Tollen's. But I suppose that Tollen's is ok, now that I understand how it works :biggrin: