Unit 4 - Laboratory Techniques and their Application
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Unit 4 Aim B: Preparation and Testing of Ethyl Ethanoate (DISTINCTION)
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Unit 4 - Laboratory Techniques and their Application
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PEARSON (PEARSON)
This is my distinction grade assignment for unit 4 aim B on the preparation and testing of ethyl ethanoate, including the industrial manufacture. All criteria were met and I was awarded distinction.
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Unit 4 - Laboratory Techniques and their Application
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Part A – Lab Report
Ethyl ethanoate is a carboxylate ester (1) which is often used in glues and nail polish removers. It can
be synthesised from ethanoic acid, CH₃COOH, and ethanol, CH₂H₅OH. When ethanoic acid, a
carboxylic acid, reacts with the alcohol ethanol, the OH hydroxyl group of ethanoic acid and the H
from ethanol’s hydroxyl group form H₂O, a by-product of this reaction. The remaining CH₃CO of
ethanoic acid is the ester ‘ethanoate’ and the remaining C₂H₅O of ethanol is an ‘ethyl’ group –
together they form ethyl ethanoate. This reversible reaction forms a dynamic equilibrium so all 4
substances (ethanoic acid, ethanol, ethyl ethanoate and water) are present in the mixture which is
produced. When in dynamic equilibrium, the number of reactant and product molecules do not
change, yet the reaction continues. In the beginning of the reaction, the reactants (ethanoic acid and
ethanol) are at their maximum concentrations in the solution as no products (ethyl ethanoate and
water) have been produced yet. As the products form, their concentration within the solution
increases, while the concentration of the reactants decreases. Eventually, the two concentrations
are equal – the reaction has reached dynamic equilibrium (2). A reaction in equilibrium can never be
‘completed’ as the products and reactants are being formed simultaneously, this means certain
procedures must be carried out to isolate the desired products from the solution. The equation for
this reaction is: CH₃COOH + CH₂H₅OH ⇌ CH₄H₈O₂ + H₂O.
This reaction is catalysed by concentrated sulfuric acid, H2SO₄. Sulfuric acid is selected because, as
well as increasing the rate of reaction, it also works as a drying agent to remove water from the
reaction and therefore increase yield (3). It is important to reduce the concentration of water
involved in this reaction because, according to La Chatelier’s principle, increasing the concentration
of water ‘shifts’ the reaction towards the left so less of the product is formed (4). For this reason,
concentrated sulfuric acid should be used over dilute, to minimize the water added to the solution
and therefore maximise yield.
The method utilises three main techniques: reflux, distillation and solvent extraction. Reflux allows
organic substances to be heated for a long time in a closed system – which is required to produce
dynamic equilibrium. The process involves a ‘reflux condenser’ to be attached to the flask, this
condenses vapours from the solution and allows them to drip back into the flask to prevent any loss
to the environment. The equipment needed for this includes: heat source, reflux condenser, heat
source, water source, round-bottom flask, retort stand and clamps. Anti-bumping granules or a can
be added to control boiling. While the mixture is being heated in reflux, the ionisation of sulfuric acid
in the mixture causes a water molecule to be eliminated between two alcohol molecules, forming an
ether (5). Distillation –which is used to separate liquids of different boiling points - is used to remove
the ether as it has a lower melting point (35-40°C) than the rest of the solution (~70°C). To use
distillation, a heat source, round-bottom flask, thermometer and adapter, Leibig condenser, water
source, retort stands, clamps, collecting tube and receiving flask will be needed. Solvent extraction
uses a separating funnel to separate immiscible liquids. The liquids form two layers within the funnel
– the aqueous layer and the organic layer – one of which will be drained off using the tap on the
bottom of the funnel. For this mixture, the lower, organic layer contains the desired product while
the upper, aqueous layer contains dissolved ethanoic and sulfuric acid as well as some impurities.
The two liquids are immiscible because the ester product is nonpolar while the water is polar.
, Method:
Step 1: The first step in carrying out this procedure was to set up the reflux equipment as shown in
figure 1 and combine the following reagents to a clean, dry 250cm³ round-bottomed flask: 50cm³
ethanol, 50cm³ glacial acetic acid (ethanoic acid), 10cm³ concentrated sulfuric acid (it is important to
swirl the mixture as sulfuric acid is added to produce a homogeneous solution, to prevent over-
heating as sulfuric acid is denser than the other substances, (5)) and 4-8 anti-bumping granules. The
mixture was then heated gently for 10 minutes to facilitate the reaction between ethanol and
ethanoic acid.
Figure 1: Reflux Equipment
Step 2: The next step was to rearrange the equipment for distillation, as shown in figure 2 below.
Around 2/3 of the mixture was distilled off and cooled to room temperature.
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