Equation of reaction:
Aspirin is in a class of drugs called salicylates. Some examples of its uses are as follows:
- Reduce inflammation
- Enhances uric acid elimination
- Reduce pain
- Relieves joint pains associated with arthritis and rheumatism
(Ref: A)
It is also used in a number of cases under medical supervision. This is because of its unique property anti-platelet, thinning of the blood, effect which can be used to treat or prevent the following:
- Strokes
- Heart attack
- Angina
The toxic dose of aspirin is generally measured to be greater than 150 mg/kg of body mass. Moderate toxicity occurs at doses up to 300 mg/kg, severe toxicity occurs between 300 to 500 mg/kg, and a potentially lethal dose is greater than 500 mg/kg. (Ref: B)
Hypothesis to be tested
The hypothesis of this experiment is to test the percentage yield and the melting points of an aspirin sample produced in the laboratory, and compare this value to a known data value. From the melting point we will know if the aspirin is pure. Pure aspirin has a melting point in the range of 135-1400c.
Experimental Plan
The reactants salicylic acid and acetic anhydride will be reacted together using the method and experimental technique outlined below. A small amount of Sulphuric acid will also be used. The reaction will involve refluxing and vacuum filtration. After producing the aspirin, the total product remaining will be weighed using a suitable, accurate weighing device, and the melting point will be measured using the appropriate method. The published value will be found using a suitable source, and from this comparisons can be made.
Procedure and Experimental Technique
Apparatus Required-
- Pipette
- Spatula
- Buckner Funnel/Flask
- Clamp and Clamp Stand
- Glass Rod
- Analytical balance (to 4.d.p)
- Filter Paper
- 100ml Measuring Cylinder
- Refluxing Apparatus with Condenser
- Melting point apparatus including a Capillary tube
- 0.5ml Conc. Sulphuric Acid
- Thermometer
- 80ml Acetic Anhydride
- Stop clock
- Burette
- Round-bottomed quick fit flask
- 1000ml Beaker
- 50g Salicylic Acid
- At least 750ml Distilled Cold Water
Procedure:
- Weigh an empty beaker on the analytical balance and record the result
- Measure 50g of Salicylic Acid using the analytical balance and 80ml of Acetic Anhydride using a 100ml measuring cylinder and record the results
- Using a 1ml burette carefully measure out 0.5ml Conc. Sulphuric Acid
- Mix all the above components in a round-bottom quick fit flask and stir the mixture continuously, every so often
- Outside of fume cupboard, turn the green tap on to provide water to the condensing lid
- Make sure the bottom of thermometer bulb is fully submerged at the bottom of the round-bottom quick fit flask to measure the heat of the components
- Raise the lab jack with the heating mantle on so it is directly under the round bottom quick fit flask.
- Turn the heating mantle on to number two setting, using the temperature controller to heat the components
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Start the stop clock, gently heat the mixture, at 70oC, occasionally agitate (approximately every 5 minutes) to ensure the sulphuric acid is dispersed
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Keep and eye on the thermometer to make sure the temperature does not exceed 70oC at any time
- After 30 minutes, turn the heating mantle off and lower the lab jack
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Cool the flask and its contents to about 50oC,
- Measure out 750ml of distilled water in the 1000ml beaker
- Pour the contents from the round-bottom quick flask into the 1000ml beaker
- Stir for a few minutes using the glass rod to induce crystallistation
- After sufficient amount of crystals are formed turn on the vacuum pump and start to transfer the contents of the Beaker to the Buckner filter
- Get a evaporating dish and using the analytical balance record its weight
- Carefully remove the filter paper and transfer the product, aspirin from the Buckner filter into the evaporating dish
- Re weigh the evaporating dish and record the result
- Allow the aspirin crystals to dry thoroughly and then weigh the solid and record the result
- Take a small sample and test the melting point using the correct apparatus
Hazard and Risk Analysis
When handling chemicals, there are many hazards and risk associated with them. Therefore, prior to the experiment a COSHH assessment was carried out and the relevant MSDS data was researched and printed to bring along to the experiment.
The COSHH assessment and MSDS sheets can be found in Appendix A at the end of the report.
Below is a brief overview of the hazards of the chemicals:
- Acetic anhydride is corrosive and is irritant to the eyes and skin
- Salicylic Acid is harmful if swallowed, and also irritating to eyes and skin.
- Sulphuric Acid can cause severe burns to the eyes and skin, and very irritant and dangerous if inhaled
Suitable precautions will be taken into account when using these chemicals, to use the correct P.P.E., such as a plain white lab coat, safety goggles, and rubber gloves where necessary. Whilst in the process of the experiment ensure the lab is kept tidy at all times and not to eat or drink within the laboratory.
Data
Moles = Mass/Rmm
Rmm of Aspirin = (C9H8O4) = (12x9) + (1x8) + (16x4) = 180
Rmm of Salicylic Acid = (C7H6O3) = (12x7) + (1x6) + (16x3) = 138
% Yield = (Actual yield/ Theoretical yield) x 100
Results
Weight of empty container = 166.28g
Weight of container + aspirin remaining solid product = 229.40g
Therefore, weight of Aspirin =229.40g -166.28g = 63.12g
The melting point was found to be 136.5oC
The melting point value given as a published value is shown to be 137oC, therefore the aspirin sample produced can be said to be very pure.
The reaction is a 1:1 ratio, therefore as 50g of Salicylic acid was used,
Number of moles Salicylic acid = Mass/Rmm
= 50/138 = mols of Aspirin
= 0.3623mol
To calculate the mass of Aspirin produced:
Mass = Moles*Rmm
= 0.3623 x 180 = theoretical mass
= 65.21733g
To calculate the percentage yield:
% yield = (Actual yield/ Theoretical yield) x 100
= 63.12/65.2174 x 100 = 97%
Discussion and interpretation
In comparison to the published data value, the significance is high for the purity as the melting point is within range. Theoretically, 65.2174g of aspirin should have been produced in order to ensure the product had 100% yield. However this could have been due to various errors in the experimental practical process. Systematic errors, human errors and random errors could all have reduced the accuracy of our result. Some examples of errors include:
- Reading the measurements on measuring cylinders and analytical balance
- Transferring contents of flask to the beaker. Some residue remained; therefore not all of the contents were transferred.
- More time would allow reaction to occur for longer and to completion
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Difficult to control the temperature at a constant 700C
Conclusions and Recommendations
In conclusion the results gained from the experiment prove to be a success. This is due to the purity being relatively high and the percentage yield being so high. So overall the experiment was a success. Our aims have been achieved which we set out earlier in the executive summary.
Nomenclature List with units
Rmm - relative molecular mass
g - weight in grams
Mins - time in minutes
Mol - moles
Ml - volume milliliters
References and Acknowledgements
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A -
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B - Temple AR. (1981). "Acute and chronic effects of aspirin toxicity and their treatment". Arch Intern Med 141 (3 Spec No): 364-9.
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1 -
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2 -
Appendices
Appendix A - COSHH assessment
Appendix B - The document was word processed using Microsoft ® Word 2003
