Preparing and purifying liquid compounds - Help!?

I've been asked by my chemistry teacher to make notes on the preparation and purification of organic liquid compounds as a part of the organics topic in AS chemistry. I need to know about heating under reflux, extraction using a solvent in a separating funnel, distillation, drying with anhydrous salt, and boiling temperature determination. I'm ok with four of the five stages but I cant find anything on extraction in a separation funnel (the separation funnel being the issue here). Does anyone have any notes on this I could use? Also, are these all stages of one process or five different organic techniques to be inferred separately? (I thought they were one process but my revision guide lays it out in a way suggesting otherwise.)

As a bit of context my old chemistry teacher has just gone on maternity leave so my class has merged with the other chemistry class in the year, meaning we have a very big group and the books recommend by the teachers are different so I haven't got access the kind of content being looked for - neither does the internet either!

(edited 7 years ago)

Reply 1

Hajra Momoniat

Hopefully the attachment should help with the separation funnel idea.

I'm pretty sure that the distillation and reflux and the other experiments are all to do with one molecule

hat books are you looking for?

Recrystallisation of benzoic acid and melting point determination (1).pdf786.3KB

Reply 2

Chumbury

Original post by Hajra Momoniat

Thankyou

that gives me some context!

We're on the Edexcel exam board and my original class have the George Facer version of the textbook, but our new teacher and other class are using the Andrew Hunt textbook. They're similar but I think the Hunt version focuses more on the organics than Facer - which is why I struggled to find much!

Reply 3

MexicanKeith

Original post by Chumbury

Thankyou

Hi, I'll try to give you a brief overview of using a separating funnel to extract product.

The idea is, you have 2 solvents in your separating funnel, your product is very soluble in one solvent and hopefully impurities are very soluble in the other solvent.

This means that you can separate your products by separating the layers of solvent in the funnel.

Often this method is particularly good if one of your products has an carboxylic acid group, or a basic amine group.

So, here's an example.

say you had 2 products you wanted separated, one acidic and the other one neutral (ie neither acidic nor basic), lets say they're dissolved in ethyl acetate (ethyl ethanoate).

the first thing you could do would be to wash (ie put it in a separating funnel) with NaOH(aq), the base would deprotonate the acid leaving the charged conjugate base with a -CO2- group.

now, as you shook up the two solvents (water and ethyl acetate) the charged acid species would be dissolved into the hydrogen bonding water which can stabilise it best. the neutral compound would rather stay in the ethyl acetate (remember like dissolves like, so polar species like polar water) so you would have 2 layers.

Now the water (more dense) would sink to the bottom and you could run this off into a flask with the acid in it, the remaining ethyl acetate would then contain the neutral compound only. The solvent could then be evaporated off to leave the neutral product.

now to get back the acid compound we need to reprotonate the acid group we just deprotonated, so you could add excess acid, then using the same process, this time wash with clean ethyl acetate.

The acidic species would move from the water to the ethyl acetate because it is no longer charged and hence it's preference for water is removed.

you'd then have your acid separated in ethyl acetate, which again you could boil off to leave pure acid.

hope that makes sense as an example, just ask if anything needs clarification! :smile:

Preparing and purifying liquid compounds - Help!?

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