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Hydrolysis of an ester

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A-Level Chemistry Coursework: Hydrolysis of an ester Ying-Jun Ng For the hydrolysis of methyl benzoate, care must be taken throughout the procedure as a number of dangerous substances are being used. During the procedure a labcoat, goggles, and gloves must be worn throughout. Specific safety instructions for chemicals or procedures are explained in the step that they are introduced. Observations, readings, and necessary safety precautions are discussed in the same order as the procedure was carried out in. 1. Safety: Methyl benzoate is harmful is inhaled or is it gets into contact with the skin or eyes or if swallowed. So it is necessary to carry out the entire procedure in a well-ventilated area and gloves and goggles must be worn. ...read more.


Observations: The liquid turned from cloudy to clear upon heating. 3. Safety: Hydrochloric acid is a corrosive substance but at 2mol dm-3 it is an irritant to the skin, so there must be extra care throughout to ensure that no spillages occur and goggles must be worn. Observations: Before the addition of methyl orange indicator the liquid was transparent and appeared to have an oily texture. The methyl orange indicator turned the liquid bright orange, and then with the addition of hydrochloric acid the solution turned a bright pink colour. After filtering the solution, a light/pale pink precipitate was formed. Readings: The mass of the solution before addition of the acid was 22.1g (solution only-excluding conical flask mass.) ...read more.


Observations: The samples melted into a white liquid, which evaporated upon more heating. Reading: The samples placed on the aluminium block begun to melt at 119oC and had completely melted when the temperature was122oC. 6. Readings: The dry product weighed 0.87g. The yield is worked out as follows- Theoretically - The density of methyl benzoate is 1.094g/cm3. Therefore as 2.0 cm3 of methyl benzoate is used this converts into 2.188g. Moles of methyl benzoate = 2.188 = 0.01608823529 mols 136 Following the equation There is a 1:1 ration of mols of methyl benzoate to mols of benzoic acid. Therefore theoretically there should be 0.0160882359 mols of benzoic acid as well. Actual Moles of benzoic acid = 0.87 = 0.007131147541 mols 122 Percentage yield = Actual moles of benzoic acid x 100 Theoretical Moles of benzoic acid = 0.007131147541 x 100 0.01608823529 = 44.32523153 = 44.3% yield (1dp) Reference: Density of methyl benzoate obtained from http://en.wikipedia.org/wiki/Methyl_benzoate ...read more.

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The candidate responds to the aim of the experiment okay with observations and weights and calculations all being correct. They should have repeated the experiment rather than rely on one set of results to show accuracy in the experiment. The ...

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Response to the question

The candidate responds to the aim of the experiment okay with observations and weights and calculations all being correct. They should have repeated the experiment rather than rely on one set of results to show accuracy in the experiment. The missing evaluation, introduction and conclusion make the format of the essay harder to follow.

Level of analysis

The introduction is missing which sets out what the candidate is going to do in the experiment and an introduction is good for basic scientific principles behind the experiment and to introduce the essay. The candidate does not supply a method which is confusing, but rather explains observations at each step and the safety that should be observed, observations also included accurate weights. Calculations are correct. The candidate should provide an evaluation and conclusion to show their understanding of the science behind the experiment and how to improve it.

Quality of writing

The layout is quite confusing as the method is not mentioned so the steps and safety precautions and observations are hard to follow. One reference is used, and the candidate should provide a wider range. Punctuation, grammar and spelling are fine.

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