Making Aspirin

In this task we were asked to synthesise aspirin from salicylic acid (2 – hydroxybenzoic acid) and ethanoic anhydride (CH3COOCOCH3) in a laboratory scale and prepare a pure silver chloride sample from the solutions of silver nitrate (AgNO3) and sodium chloride (NaCl) of known concentrations. Now I am going to describe the preparation of these two items and estimate the purity of one of my samples.

Preparation of aspirin: Now I am going to explain the preparation of the aspirin;

Materials : (a) ethanoic acid (b) ethanoic anhydride (c) salicylic acid (d) water cooled condenser (e) filter paper (f) Buchner funnel (g) vacuum oven (h) melting point recorder machine etc.

Procedure

Firstly we mixed 5 ml of ethanoic acid with 5 ml of ethanoic anhydride in a 50 ml round bottomed flask.
After that we added 5 g of 2- hydroxybenzoic acid and a few anti – bumping stones .
Then we attached a water cooled condenser and reflux the mixture for 30 minutes over a Bunsen and gauze.
Then we pour the mixture slowly into 100 ml of cold water which is being stirred vigorously.
After that we removed the 2 – ethanoyloxybenzoic acid by filtration through a Buchner funnel.
Then we removed the product from the fume cupboard and dried it in a vacuum oven at about 80 degree Celsius.
Then we weight the dried product and recorded its melting point.

Chemical reaction:

Equation 1: Synthesis of Aspirin

Preparation of silver chloride: Now I am going to explain the preparation of silver chloride;

Materials : (a) silver nitrate (b) sodium chloride (c) cylinders (d) beaker (e) glass rod (f) filter paper (g) Buchner funnel (h) oven etc.

Procedure

Firstly we had to measure 10 cm3 of silver nitrate and sodium chloride solutions in two separate measuring cylinders.
Then we pour both solutions in a beaker provided.
After that we stirred the solutions with a glass rod for two minutes.
Then we weight an empty filter paper and recorded its mass which is 0.1425 g.
Then we filtered the content through a Buchner funnel.
After that we collected the solid in the filter paper.
Then we dried the solid in an oven.
Finally we weight the solid with the filter paper to get the mass of solid.

Chemical reaction:

AgNO3 (aq) + NaCl (aq) = AgCl(s) + NaNO3 (aq)

After the experiment we have found the mass of aspirin. The mass of aspirin = 2.9734 g (Practical)

Calculations:
Step 1: Now we are going to calculate the moles of 2- hydroxybenzoic acid from its mass.
The mass of 2- hydroxybenzoic acid C6H4(OH)COOH is = (12 x 6) + (1 x 4) + (16 + 1) + (12 +16 + 16 + 1) = 138 g
Moles of 2- hydroxybenzoic acid = (5 / ...

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Chemical reaction:

AgNO3 (aq) + NaCl (aq) = AgCl(s) + NaNO3 (aq)

After the experiment we have found the mass of aspirin. The mass of aspirin = 2.9734 g (Practical)

As 1 mol of 2 – hydroxybenzoic acid doing reaction with 1 mol of ethanoic anhydride and making 1 mol of 2 – ethanoyloxybenzoic acid which is aspirin, so that the moles of aspirin will be same number of moles of 2- hydroxybenzoic acid.

Step 2: Now I am going to calculate the theoretical mass of aspirin from its moles.
We know that mole = (mass / relative molecular mass). The relative mass of 2-ethanoyloxybenzoic acid (C9H8O4) = (12 x 9 + 1 x 8 + 16 x 4) = 180g. So the mass of aspirin = (0.036 x 180) = 6.48g.

Step 3: Now I am going to calculate the % yield from the results we have already got.

After the 2nd experiment we have found the mass of silver chloride. The mass of silver chloride is = 0.2542 g (practical) with filter paper and the mass of filter paper is 0.1425 g, so the mass of silver chloride is = (0.2542 – 0.1425 ) g = 0.1117 g.

Calculations:
Step 1: Now we are going to calculate the moles of silver nitrate from its mass.
Concentration of silver nitrate is 0.1 moldm-3 and the volume of silver nitrate is 10 cm3.
So the moles of silver nitrate is = 0.1 moldm-3x (10/1000) dm3
= .001 moles.

The number of moles of silver chloride is the same number of moles of silver nitrate (1: 1 ratio). So the moles of silver chloride = 0.001 moles.

Step 2: Now I am going to calculate the theoretical mass of silver chloride from its moles.
The relative mass of silver chloride (AgCl) = (108 + 35.5) = 143.5 g
so the mass of silver chloride = (.001 x 143.5) = 0.1435 g.

Step 3: Now I am going to calculate the % yield from the results we have already got.

Estimate the purity of aspirin: We can find the purity of any substances by determining the melting point which is the book value. The melting point of aspirin is about 1360 C which is the book value. The aspirin we made in the experiment was kept in the melting point apparatus to find out its melting point. The melting point apparatus which has a heating block inside to heat the sample. A small glass window in front of one instrument through which we can see what we put inside the instrument. There is a small block on top of the instrument with three holes in which we can put the capillary tube filled with the sample. One end of the capillary tube is sealed. There is a place at the back of the capillary tube slot to insert the thermometer.

I took a little bit of sample in the capillary tube and put it inside the melting point apparatus. Then I switched the machine on and used the heating and lamp option to heat the sample slowly. After a while when the temperature was 1280 C to 1290 C the colour of the aspirin was changing and it started to melt and its melted completely about 1310 C temperature. If the temperature was more than the book value or less, the aspirin would not be pure but as the temperature is quite closer to its melting point book value, so that it is not quite pure.

Now I am going to explain the factors that affect the percentage yield and the purity of aspirin and how to improve them.

The factors that affect the percentage yield: Actual product yields will always be somewhat less than theoretical, due to a variety of application factors such as ambient temperature and humidity, application technique, etc. This is true regardless of manufacturer.
As we have done this experiment in the laboratory, so we may have these factors that affect the percentage yield are explained below;

Equipments used: We had to use different equipments to do this experiment. Those equipments we used they might not be quite accurate or they might have some kind of errors already. So that can have a big impact in the experiment we did. So that’s for we didn’t get quite enough products we expected. That’s how it did affect our yield percentage.
Instructions followed: As we were given the instructions already to use. So we had to use them but the instructions may not be followed properly. If we have done any sort of mistakes to follow the instructions, so that it can affect our yield percentages.
Collection method: The way we have collected the data and all the results may not be perfect. In the collection time if we have neglected any small amount of any products, that can have a affect in the yield percentages. So the collection method should be quite accurate.
Step involved in the experiment: We already had the procedure written in the paper. We had to follow the procedures to make it right. But if we were unable to follow this steps, then we will not get the expected amount of products. So we should have done these steps correct. We might not have done them quite accurate or perfect.
Reaction time: We know that we had to attach the water cooled condenser and refluxed the mixture for 30 min over a Bunsen and gauze. If we did that less or bit more longer than that, so it may affects the reaction time and that can affects in the actual products.

Personal errors: Personal error is another factor that can affects the percentage yield. We all do some personal mistakes. In the experiment we may not be able to weigh the equipments properly or got their (solutions) volume wrong or not quite right. We may put our products everywhere in the filter papers etc.

The factors that affect the purity: The factors that can affect the purity of the products are explained below;

Cleaning: As we did the experiment in a lab, so we discovered that using more water to rinse the solution causes very much Aspirin to be lost in the purification process. So we have to do cleaning very carefully.

Amount of reactant added: As we were supposed to mix 10 cm3 silver nitrate with same amount of sodium chloride in a beaker, so we had to make sure it is the right amount of reactant in the beaker otherwise the purity of the products will not be good enough. In the 2nd experiment we had to put 5g of salicylic acid in the mixture, so we had to do that perfect as well. If we haven’t done them right, the purity of the products will not be quite satisfactory.

Reaction time: The reaction time of any reaction should be done with care. If the reaction time is so quick or so slow then the produced products will not be pure enough to deal with. That’s why we have to make sure that we have done these things right to get the pure products.

How to improve them: To improve these things explained above, we have to follow some steps involved;

First of all we have to make the work plan to do this experiment right. Then we have to follow the plans. Then we have to follow the procedures and steps involved in the experiment. We have to make a list of what might go wrong in the experiment and then we have to do them carefully.

We have to make sure that when we keep this solid products in the oven, that nobody can open them for a minute or something, then the purity will be very bad.

All the major factors involved in this experiment, we have to do them perfectly and by making the work plan, and by applying it correctly we can easily improve this experiment and get more products yield and more purified.

Peer Reviews

Here's what a star student thought of this essay

crystalclearmagic

22nd of Mar 2012

Quality of writing

The spelling, grammar and punctuation were fine. I would suggest using bullet points to clearly space out of the sub sections, although this is personal preference which I think would make each point clearer and easier for examiners to read. This said, the piece of work is presented clearly nevertheless. The technical terms could be defined in a glossary to demonstrate further understanding, although again this is not compulsory. The student exceeds the expectations of this level of work as they have explained each step very clearly and obviously has a very solid understanding of the topic. On a last note, I would say that the formatting for 'degrees C' should be relooked at as the format should not be a 'zero' as a superscript with a capital 'C'.

Level of analysis

The student shows a very clear understanding of the topic and analyses the topic well. S/he supports the topic well with explanations to each step of the experiment and calculations that followed on from the experiment. Their judgements are clear and suitable from the experiment and the appropriate conclusions were reached. I would suggest that they had laboured the word 'we' in the piece of work - instead of "we add" just write "add". This makes the coursework more 'formal' and suitable for the level of qualification in my view.

Response to question

The student sets out his/her answer very clearly and logically and therefore, the answer has been attempted in a logical and sensible manner. The response is very explicit and clear. The explanations in the calculations section is perfect and guides the reader (examiner) through the process very clearly. The only area I can fault in this piece of work is the lack of referencing. Although all chemists know what is meant by "book value", perhaps it is best to reference where this value came from (in this case, as referenced in the textbook that the student has for their exam board). Also any diagrams must be sourced and referenced as this stops any infringement of copyright from occurring in this piece of work.

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