10a: perperation of an organic liquid Flashcards
equation for the reversible reaction in this practical
alcohol + organic acid = ester + water
why is concentrated H2SO4 added to the reaction mixture
to remove excess water formed and to prevent a backwards reaction (concentrated sulphuric acid access a dehydrating agent)
What can we use instead of an organic acid that will not need concentrated sulphuric acid
The problem can be overcome if an anhydride derivative is used instead of an organic acid. The use of an anhydride avoids the formation of water so no backward reaction/Ester hydrolysis occurs.
what is the equation when an anhydride derivative is used
pentan-1-ol + ethanoic anhydride = pentyl ethanoate + ethanoic acid
alcohol + anhydride = ester and carboxylic acid.
What is the procedure for preparing an organic liquid
1: place the anti-bumping granules in a round bottom flask and add the alcohol. Set up the apparatus for reflux and Pourin the ethanoic anhydride down the Liebig condenser.
2: warm them boil for 10 minutes
3: cool then transfer to a separating funnel.
4: add 25 cm³ of distilled water, shake, stopper the funnel to allow for the layers to separate and discard the lower layer.
5: add 10 cm³ of sodium hydrogen carbonate to the funnel. Shake. And allow the carbon dioxide produced to escape at frequent intervals and discard the lower aqueous layer each time
6: Transfer the ester to a quick fit conical flask and add a spatula of sodium sulfate and stopper the flask. Dry the product by swirling the flask and its contents for about five minutes
7: filter the dry ester into a clean 50 cm³ Kwik fit flask three small fitted for now with a small plug off Cottonwool.
8: Set up the apparatus for distillation with anti-bumping granules, a round bottom flask, a collecting fraction that boils between 135 to 140°C. In a pre-Weighed Kwik fit conical flask which has been immersed in a beaker of ice record the mass of the conical flask.
9: after the distillation is complete record the mass of the quick fat conical flask.
Why are anti-bumping granules added
They prevent the formation of big bubbles as they provide a large SA for bubbles to form.
They make boiling occur more evenly, without the sudden violent release of vapour
what are two ways you can increase the yield
You could set the temperature to boil at a certain temperature where the other reagent doesn’t boil
you could cool the product in an ice bath to prevent the products from evaporating
Suggest two reasons why the yeild is less than 100%
could’ve been an incomplete reaction between the alcohol and the anhydride
we could have lost yield in filtration/cotton wool/ lost yeild on equipment whilst transferring
What are to the waves at the purity of organic liquids may be assessed
You could use a radioactively labeled compound for example carbon 13. This can highlight the physical and chemical properties of a particular product that has been formed. Compounds that combine with carbon will be radioactively labeled.
you could use boiling points determination. Most chemical products have defined boiling points, if the boiling point of a particular chemical is increased there’s a greater chance that the chemical is not pure.
How can you check that the sample is More pure
if the sample is very pure the melting point will be sharp/the same as quoted in data books
