RP10 (2) - Preparation of a Pure Organic Liquid Flashcards
Describe how to purify an organic liquid (ester)
Put the distillate of impure product into a separating funnel.
Wash product by adding either sodium hydrogencarbonate solution , shaking and
releasing the pressure from CO2 produced. or saturated sodium chloride solution
Allow the layers to separate in the funnel, and then run and discard the aqueous layer.
Run the organic layer into a clean, dry conical flask and add three spatula loads of drying agent (e.g. anhydrous sodium sulfate, calcium chloride) to dry the organic liquid.
When dry the organic liquid should appear clear.
Carefully decant the liquid into the distillation flask
Distil to collect pure product
What does sodium hydrogencarbonate do
Neutralises remaining acid
What does the sodium chloride do
Helps separate the organic layer from the aq layer
Which layer will be on the top and why
The organic layer will usually be on the top. The layer with lower density will be the upper layer.
Conditions for the drying agent
Insoluble in organic liquid
Should not react with the organic liquid
What does sulfuric acid act as in preparation of ester
Catalyst
How is sulfuric acid added
Drop by drop to prevent uncontrolled boiling over
What is anhydrous calcium chloride/ sodium sulfate/ magnesium sulfate acting as
Drying agent
Describe the method for preparing and purifying an ester
Propan-1-ol (50 cm3) and ethanoic acid (50 cm3) are mixed thoroughly in a 250 cm3 round-bottomed flask.
Concentrated sulfuric acid (10 cm3) is added drop by drop to the mixture, keeping the contents of the flask well-shaken and cooled in an ice-water bath.
When the acid has all been added, a reflux condenser is fitted to the flask and the mixture gently boiled over an electric heating mantle for about 30 minutes.
The mixture is cooled, and the apparatus rearranged for distillation.
The crude ester (about 60 cm3) is distilled off.
The distillate is placed in a separating funnel and shaken with about half its volume of 30% sodium carbonate solution, with the pressure being released at intervals.
The lower aqueous layer is then discarded.
The crude ester is shaken in a separating funnel with about half its volume of 50% calcium chloride solution, which removes unreacted alcohol.
The lower layer is discarded.
The ester is run into a clean, dry flask containing some anhydrous calcium chloride and swirled.
The ester is filtered into a clean, dry flask, with a few anti-bumping granules, and distilled.
The fraction boiling between 100°C and 103°C is collected.
What does sulfuric acid act as
Catalyst
Why is conc H2SO4 added drop by drop and cool
It is an exothermic reaction so this prevents uncontrolled boiling over
What happens in reflux
The reactant vapours are condensed and returned to the reaction mixture
