Unit 4 - Laboratory Techniques and their Application
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4B - Laboratory techniques and their application DISTINCTION
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Unit 4 - Laboratory Techniques and their Application
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Unit 4 - Laboratory Techniques and their Application
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Ammara Aslam
12ANC
Laboratory techniques and their application
Esters are organic compounds formed from the condensation reaction of a carboxylic acid
and an alcohol, a strong acid catalyst should also be added. Carboxylic acids have an
unpleasant smell. They are also called weak acids as they are not as reactive as strong
acids (e.g sulfuric acid). When carboxylic acids react with metals,carbonates and alkalis they
show the characteristic reactions of acids. Alcohols only have C-C and C-H bonds which
makes them unreactive towards aqueous reagents, this is because those bonds are very
hard to break which makes them unreactive.
Esters have a sweet smell and are very useful. esters are used in industry as solvents and
when making polyesters they are used as a reactant . esters give fruits their smell and are
common in nature
We carried out a practical in which we prepared and purified a sample of an organic liquid
which was ethyl ethanoate and we also tested its purity. Ethyl ethanoate is an ester which
has a strong smell and is used in nail varnish remover. The alcohol we used was ethanol
and the carboxylic acid we used was ethanoic acid react to form ethyl ethanoate and water.
To speed up the reaction sulfuric acid is added and used as a catalyst, it also absorbs the
water producing more ester.7
Ethanol:C2H5OH Ethanoic acid:CH3COOH
6
We first prepared ethyl ethanoate in stage 1 by following the method:
1)Add a few anti-bumping granules to a 50cm3 pear shaped flask .
2)In a fume cupboard we then add 10cm3 ethanol,12cm3 of glacial ethanoic acid and 15
drops of concentrated sulfuric acid to the flask.
3)place a 250cm3 beaker containing some water on a tripod and gauze over a bunsen
burner
4) clamp the pear-shaped flask in the beaker of water so that the reaction mixture is below
the water line
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,Ammara Aslam
12ANC
5)Add a condenser so that it is set up for heating with reflux. Clamp the condenser.
6)light the bunsen burner to the water bath. raise the temperature of the hot water until the
mixture in the flask is gently boiling . continue the gentle boil of the reaction mixture by
removing the hot water bath.
Ethanol is flammable so it should be kept away from the
bunsen burner. rubber gloves should be worn when handling
with sulfuric acid due to it being corrosive and hazardous.
Bunsen burner flame should be blue when in use and on
orange flame when not in use. Eye protection should be worn.
Anti-bumping granules are used in the mixture to make it boil
more evenly by preventing the formations of large gas
bubbles as anti-bumping granules provide nucleation sites for
smaller bubbles to develop slowly and not too vigorously,
preventing rapid boiling of a liquid and preventing it bubbling
over. A fume cupboard was used to “ control exposure to
airborne contaminants such as toxic, offensive or flammable
vapours, gases and aerosols” The organic reaction would be
very slow which is why we used heat, for it to then react at a
more appropriate rate. Due to the chemicals in the reaction being very volatile the reactants
and products are evaporated into the atmosphere, giving it a very small yield. We used reflux
to minimise this. Reflux uses a condenser to recondense the vapors back into the flask.
Refluxing is an extremely important step in preparing ethyl ethanoate because it allows for
longer reaction time so the reaction can fully complete. Water flows through the outside parts
of the condenser which cools down gases causing them to condense and drip back down
into the flask so the unreacted compounds can then react, this maximises the purity of the
product. We used a round-bottomed flask instead of a pear-shaped flask because we used a
heating mantle instead of a bunsen burner simply because it was easier to select specific
temperatures. 1,7Once the reaction was complete it was now an impure ester and needed to
go through separation techniques in order to purify it.
Reflux is widely used in many different industries, for example oil,gas and petrochemical
industry to improve distillation. Large scale distillation is used to separate mixtures of organic
liquids, but this does not always produce a pure product so reflux is used to further
evaporate and condense the distillate which increases the purity. The distillate is then heated
and the vapours will be collected and collected into a reflux drum. Any vapours which are
travelling upwards are also condensed due to condensed liquid falling back into the reflux
drum cooling the vapours causing them to also condense. This creates a more efficient
separation of materials which have different boiling points.1,7
Industrial distillation and reflux:
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, Ammara Aslam
12ANC
3
The reflux system in the distillation column allows upflowing vapors to cool and condense
which increases the efficiency of the distillation column. Temperature is controlled at the
condensers outlet so the reflux makes sure to return the components with higher boiling
points to the still and components with a lower boiling point go to a secondary condenser
Reflux is used to produce alcohol drinks so it ensures impurities and unreacted substances
are returned to the reflux still producing higher quality drinks.3
The ester produced in stage 1 is not pure, partly due to the reaction being reversible which
prevents the reaction from going to completion. Side reactions occurring are also possible
which produce by-product. This is why a separating funnel is used, as it removes most of the
impurities from the liquid ester.
Large amounts of ethyl ethanoate are made in industry since it is such a useful product.
There are several different processes that can be used for example tishchenko reaction
which is a disproportional reaction of ethanal simultaneously. The temperature for the
reaction is 0-5 degrees celsius in the presence of aluminium alcoholate as a catalyst. The
conversion of ethanol is high, up to 98perecent into the ester ethyl ethanoate giving a higher
yield.
The process we used was the esterification reaction,esterification of ethanoic acid with
ethanol in the presence of acid catalysts (sulfuric acid) because we only needed to make a
small amount. This process can be used as a batch process or a continuous process.
Distillation is used to remove water formed in the reaction. Maximum conversion of ethanoic
acid should be achieved (about 95%), this is very important. For batch procedures a single
reactor is filled with ethanoic acid and ethanol, sulfuric acid catalyst is added and as the
reaction goes on water is removed. large quantities of esters can be made from this method.
For batch processes reactors must hold very large volumes of reactants, heating coils are
used to heat the reactants.7
When the continuous process is used it is often for large quantities of esters to be produced.
Streams of the reactants are mixed into a reaction chamber and the product is removed at
3
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