Chemy102-20B Experiment 10 lab report PDF

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Experiment 10 – Preparation of Ethyl ethanoate (ethyl acetate)...

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1/10/2020

Shereen Bakshi

Lab: 2-5pm, Thursday Experiment 10 – Preparation of Ethyl ethanoate (ethyl acetate)

Introduction Ethyl ethanoate (ethyl acetate) is an ester. The general method of ester preparation can be summarised as the reversible reaction: ‘acid + alcohol → ester + water’. Concentrated sulphuric acid is used as a catalyst in the reaction that removes water from the right hand side of the equilibrium, increasing the yield of ester. The reaction is slow and reversible. It is a hydrolysis reaction. CH3COOH + C2H5OH → CH3COOC2H5 + H2O Calcium chloride removes water by forming a series of hydrates; it also reacts with alcohols to form similar compounds, and can thus remove unchanged ethanol in the crude ethyl ethanoate. The calcium chloride solution added first in step 6 reacts with excess ethanol, when the solid is added in step 7 it removes water. In this experiment we react a carboxylic acid and an alcohol under acidic conditions to form the corresponding ester, with catalysis by sulfuric acid. Experimental Firstly, we set up a reflux apparatus and ensure that the heating is turned off. Next, we turn the water on to a moderate flow before adding any of the reagents. Then, we add 5-10 boiling chips, 15 ml of ethanol, 15 ml of glacial acetic acid and 3 ml of concentrated sulfuric acid. Then the mixture of ethanoic acid, ethanol and concentrated sulfuric acid is gently heated by turning on the heating mantle. We keep it under the reflux for 20 minutes, once it starts to boil. Next, we let the mixture cool down for a while and turn the heater off but not the condenser water. Then, in the fume hood we pour the reaction mixture into a 100ml separating funnel and we rinse the round bottom flask with ethanol and let it dry. In the fume hood, we slowly add 10ml of 2M sodium carbonate solution and carefully upend the separating funnel and release the pressure. We keep shaking the reaction until no more pressure can be released. Then, we immediately discard the bottom aqueous layer in the sink. We follow the same procedure of adding 10ml of water, followed by discarding the aqueous layer and adding 10ml of calcium chloride followed by discarding the aqueous layer. Now we pour the ethyl ethanoate into a flask and add a few spatulas loads of anhydrous sodium sulphate. we put the stopper and shake again until the liquid goes clear which indicates that it is dry. We then decant the dry liquid and add 5-6 boiling chips. We assemble the distillation apparatus and start the process. We collect the distillate in the boiling range 74-79oC (pure ethyl ethanoate).

Results and Discussions Ethanoic acid and ethanol reacts to form ethyl ethanoate. The mixture needs to be heated under reflux to avoid loss of volatile substances. The distillate contains impurities such as ethanol and ethanoic acid. The distillate boiling range was between 74-79oC, whereas, it was observed that ethyl acetate starts to boil at about 68oC onwards and that’s when we begin to collect it.

Practical Yield: 8.29 g The theoretical yield is the maximum possible yield assuming that the reaction leads to completion, and that there are no losses in isolation of the product Theoretical yield This requires us to search up the density of ethyl acetate on internet. The density of ethyl acetate is 902 kg/m3[ CITATION Eth20 \l 5129 ].

902 kg /m 3=

902 X 1000 g 1000 X 1000 ml

= 0.902g/ml VEthyl Acetate= 15ml m=DV= 0.902g/ml X 15ml = 13.53

Percentage yield

practical yield × 100= percentage yield theoretical yield 8.29 g × 100=61.27 % 13.53 g

The percentage yield is less than 100%, indicating that the product might not be in its purest form and that it requires to go through the process of distillation again. An important reason could be that in the separating funnel, the mixture may not have been able to completely react which means that there are some impurities still present in the product. Another reason is that while running off the lower layers from the separating funnel, a little bit could still have been left in the separating funnel as it is hard to look at it and get rid of the exact accurate amount therefore, leading to contamination of the mixture.

References Ethyl acetate. (2020, October 7). Retrieved from WIKIPEDIA: https://en.wikipedia.org/wiki/Ethyl_acetate...