Aspirin Lab
Abstract
For the amount of aspirin in a commercial tablet to be determined, different solutions of acetylsalicylic acid mixed with NaOH were created at different concentrations. All the different solutions were then analysed using Novaspec photometer, which allowed for a graph to be created and a line of best fit to be made. The amount of aspirin in a commercial tablet was found to be 350mg.
Introduction
The molecular formula for aspirin, also known as acetylsalicylic acid, is C9H8O4. It is most commonly used as an anti-inflammatory, fever and painkilling drug, and was originally discovered in the bark of the willow tree in 1763 by Edward Stone (Monash University, Department of Epidemiology and Preventive Medicine, 2010). Aspirin, also known as …show more content…
acetylsalicylic acid, works by lowering the levels of prostaglandins in the body, which helps reduce inflammation and fever. Prostaglandins are produced when damage to the body occurs; it helps the tissue, or other damaged body parts, to heal quickly (Society for Endocrinology, 2012). The Medicine Net (2014) states that the way aspirin works is by blocking the enzyme that creates prostaglandins, which then causes the levels of prostaglandins to drop, therefore reducing the inflammation. The amount of aspirin contained in a commercial tablet differs with each one; however, there is a strict limit on how much aspirin the manufacturers need to have in their tablets. In recent years, this limit has been tightened further to prevent large differences in content. The limit is currently between 95.0%-105.0% of the amount of aspirin shown on the instruction leaflet, as stated by the British Pharmacopoeia Commission Secretariat of the Medicines and Healthcare Products Regulatory Agency (2014). However, this does not mean that in a commercial aspirin tablet 100% of the tablet is aspirin, as other substances are also found in commercial tablets, such as; lactose, potato starch, and talc. There are also certain procedures performed to check that commercial aspirin tablets contain aspirin, and in the correct amounts. There are many different tests that can be performed to check for the purity of aspirin: since; as pure aspirin has the melting point of 138oC-140oC, the sample can be melted and the melting point recorded and compared to this figure (Osborne, C. & Pack, M., 2003).
Experimental
The aspirin standard solution was prepared first. 0.4833g of acetylsalicylic acid was weighed out and dissolved in a minimum volume of NaOH solution in a weighing beaker. The solution was poured into a 100ml volumetric flask and the weighing beaker was continuously rinsed with NaOH. The washing was then poured into the 100ml volumetric flask until all the acetylsalicylic acid has been transferred. The flask was filled to the 100ml mark with the NaOH solution. A stopper was inserted, and the flask was shaken.
An aspirin tablet was crushed up with a pestle and mortar and the powder was dissolved in a minimum volume of NaOH. The solution was transferred into a 100ml volumetric flask, and the pestle and mortar were washed with NaOH, the washing was poured into the volumetric flask. The flask was filled up to the 100ml mark with NaOH solution.
The remaining standards were prepared by adding 2ml, 4ml, 6ml and 8ml of diluted aspirin standard into 4 different test tubes. The NaOH was also added into the test tubes in 8ml, 6ml, 4ml and 2ml volumes, which produced a 10ml volume solution in each test tube.
A single cuvette was used to measure the absorbance of all the different solutions using a Novaspec photometer at 360 nm wavelength. A cuvette was filled ¾ full with NaOH (blank) solution and placed in the photometer to set the reading to 0. The NaOH was poured out of the cuvette, and rinsed out with the next solution. The next solution was then poured into the cuvette and analysed in the photometer for the absorbance. All the other solutions were analysed following the same steps as the first one. The results were recorded in a table.
Results
Table 1: the results of absorbance for the solutions tested
Solution Aspirin concentration/g per 100ml Absorbance
Blank (NaOH) 0.000 0.000
2ml standard in 10ml 0.0966 0.038
4ml standard in 10ml 0.19332 0.060
6ml standard in 10ml 0.28998 0.080
8ml standard in 10ml 0.38664 0.101
Aspirin standard solution 0.4833 0.108
Tablet solution 0.3500 0.100
The aspirin concentrations were calculated as follows:
C1 x V1 = C2 x V2
2ml standard in 10ml had an absorbance of 0.038; we are working out C2, which is the concentration.
0.4833 x 2 = 10 x C2
0.9666 = 10 x C2
0.966610 = 0.09666g per 100ml
A graph was drawn by plotting the absorbance of all the solutions measured, against their concentration. From this graph, the concentration of aspirin in the tablet solution was found to be 0.3500. This was calculated by drawing a straight line from its absorbance of 0.100 to the point where it crosses the drawn line of best fit. The point at which they met was read to be 0.3500, which gave the concentration of the tablet to be 0.35g per 100ml.
The mass of the aspirin in the tablet was found to be 350mg using the following calculations:-
It was found that the aspirin concentration of the tablet was 0.35g per 100ml. The volume in which the tablet was dissolved was 100ml, so the mass of the tablet used was 0.35g.
0.35g x 1000= 350mg
Table 2: The mass of aspirin in the tablet found by the whole
class.
Mass of aspirin in the tablet (mg)
350
370
114
86
248
580
445
598
563
602
238
344
598
With the help of the table with all of the values found by each individual student, the average has been calculated to be 395.077mg.
((350+370+114+86+248+580+445+598+563+602+238+344+598))/13 = 395.077mg
Discussion
Using my results and graph, the mass of aspirin in the aspirin tablet was found to be 350mg. The mean value for the mass of aspirin found using all the class results was 395.077mg, which is 45.077mg more than my results have shown. This is fairly close, as some of the results from other students were found to be more than 100mg over the average. The mean of the class was affected by some high results (602mg), but also by some lower results (86mg).The true value of the aspirin was, however, lower than both my result and the class average, as the true value was 300mg. The true value shows the mass of pure aspirin in the tablet and does not include other ingredients, which increase the mass of the whole tablet to 344mg. Other ingredients in the tablet include: lactose, potato starch and talc, which have an overall mass of 44mg (344mg-300mg= 44mg). This makes the percentage of aspirin in the aspirin tablet to be 87.21%.
There were quite a lot of errors and uncertainty in the practical, due to equipment fault and human error. The amount of errors is noticeable in the fact that the mass of the aspirin in the tablet equalled 350mg, despite the actual mass of the whole tablet being only 344mg. This suggests that my result was impossible, as it was higher than the mass of the table. This could have been due to contamination of the equipment, as the beaker or the flask could have contained other substances during the practical. Other errors include mixing the right volumes of diluted aspirin standard solution with the NaOH volume, as the glass pipette was used to transfer between 2-8ml of solutions into the test tubes. Human error could have caused wrong volumes of solution to be added, as the pipette could have contained the wrong volume as the measurement went from bottom to top on the pipette (10ml-0ml), so for 2ml the meniscus would be at 8ml. Another error could be due to air bubbles being stuck at the bottom of the pipette, which would not allow the whole volume to be drawn by the pipette. Another error could include the rinsing of the beaker, and the pestle and mortar, as they could have still had a small amount of the powder left in them, which would have interfered with the results, as the mass would have been different per 100ml, changing the concentration. The volumetric flask which was used for creating the standard solutions was of class B, and the limit for that group is within ±0.1cm3;, as the limit is so small, the uncertainty in this measurement is extremely small. The pipette used was of class A so the uncertainty was also extremely small, as the limit of that group for pipette is ±0.03cm3.
The line of best fit of the graph of absorbance against concentration only goes through one point, which suggests that the results are not extremely accurate since the points do not fit in the straight line.
Conclusion
The mass of the aspirin in the commercial tablet has been found to be 350mg, although the actual mass is only 300mg. This is due to many errors which have been mentioned in the discussion part of this report. The actual mass of the aspirin in the tablet is 300mg, this shows that aspirin makes up 87.21% of the aspirin tablet, and the other 12.88% contains other substances such as lactose, potato starch and talc. Measuring the absorbance of the solutions using a photometer is an effective way of comparing solutions of different concentrations, as it allows a graph to be drawn. This is a fairly quick process, although it needs the person performing the practical to have a full knowledge of how to use the equipment, as it needs to be zeroed (‘0’) before use.
For the amount of aspirin in a commercial tablet to be determined, different solutions of acetylsalicylic acid mixed with NaOH were created at different concentrations. All the different solutions were then analysed using Novaspec photometer, which allowed for a graph to be created and a line of best fit to be made. The amount of aspirin in a commercial tablet was found to be 350mg.
Introduction
The molecular formula for aspirin, also known as acetylsalicylic acid, is C9H8O4. It is most commonly used as an anti-inflammatory, fever and painkilling drug, and was originally discovered in the bark of the willow tree in 1763 by Edward Stone (Monash University, Department of Epidemiology and Preventive Medicine, 2010). Aspirin, also known as …show more content…
acetylsalicylic acid, works by lowering the levels of prostaglandins in the body, which helps reduce inflammation and fever. Prostaglandins are produced when damage to the body occurs; it helps the tissue, or other damaged body parts, to heal quickly (Society for Endocrinology, 2012). The Medicine Net (2014) states that the way aspirin works is by blocking the enzyme that creates prostaglandins, which then causes the levels of prostaglandins to drop, therefore reducing the inflammation. The amount of aspirin contained in a commercial tablet differs with each one; however, there is a strict limit on how much aspirin the manufacturers need to have in their tablets. In recent years, this limit has been tightened further to prevent large differences in content. The limit is currently between 95.0%-105.0% of the amount of aspirin shown on the instruction leaflet, as stated by the British Pharmacopoeia Commission Secretariat of the Medicines and Healthcare Products Regulatory Agency (2014). However, this does not mean that in a commercial aspirin tablet 100% of the tablet is aspirin, as other substances are also found in commercial tablets, such as; lactose, potato starch, and talc. There are also certain procedures performed to check that commercial aspirin tablets contain aspirin, and in the correct amounts. There are many different tests that can be performed to check for the purity of aspirin: since; as pure aspirin has the melting point of 138oC-140oC, the sample can be melted and the melting point recorded and compared to this figure (Osborne, C. & Pack, M., 2003).
Experimental
The aspirin standard solution was prepared first. 0.4833g of acetylsalicylic acid was weighed out and dissolved in a minimum volume of NaOH solution in a weighing beaker. The solution was poured into a 100ml volumetric flask and the weighing beaker was continuously rinsed with NaOH. The washing was then poured into the 100ml volumetric flask until all the acetylsalicylic acid has been transferred. The flask was filled to the 100ml mark with the NaOH solution. A stopper was inserted, and the flask was shaken.
An aspirin tablet was crushed up with a pestle and mortar and the powder was dissolved in a minimum volume of NaOH. The solution was transferred into a 100ml volumetric flask, and the pestle and mortar were washed with NaOH, the washing was poured into the volumetric flask. The flask was filled up to the 100ml mark with NaOH solution.
The remaining standards were prepared by adding 2ml, 4ml, 6ml and 8ml of diluted aspirin standard into 4 different test tubes. The NaOH was also added into the test tubes in 8ml, 6ml, 4ml and 2ml volumes, which produced a 10ml volume solution in each test tube.
A single cuvette was used to measure the absorbance of all the different solutions using a Novaspec photometer at 360 nm wavelength. A cuvette was filled ¾ full with NaOH (blank) solution and placed in the photometer to set the reading to 0. The NaOH was poured out of the cuvette, and rinsed out with the next solution. The next solution was then poured into the cuvette and analysed in the photometer for the absorbance. All the other solutions were analysed following the same steps as the first one. The results were recorded in a table.
Results
Table 1: the results of absorbance for the solutions tested
Solution Aspirin concentration/g per 100ml Absorbance
Blank (NaOH) 0.000 0.000
2ml standard in 10ml 0.0966 0.038
4ml standard in 10ml 0.19332 0.060
6ml standard in 10ml 0.28998 0.080
8ml standard in 10ml 0.38664 0.101
Aspirin standard solution 0.4833 0.108
Tablet solution 0.3500 0.100
The aspirin concentrations were calculated as follows:
C1 x V1 = C2 x V2
2ml standard in 10ml had an absorbance of 0.038; we are working out C2, which is the concentration.
0.4833 x 2 = 10 x C2
0.9666 = 10 x C2
0.966610 = 0.09666g per 100ml
A graph was drawn by plotting the absorbance of all the solutions measured, against their concentration. From this graph, the concentration of aspirin in the tablet solution was found to be 0.3500. This was calculated by drawing a straight line from its absorbance of 0.100 to the point where it crosses the drawn line of best fit. The point at which they met was read to be 0.3500, which gave the concentration of the tablet to be 0.35g per 100ml.
The mass of the aspirin in the tablet was found to be 350mg using the following calculations:-
It was found that the aspirin concentration of the tablet was 0.35g per 100ml. The volume in which the tablet was dissolved was 100ml, so the mass of the tablet used was 0.35g.
0.35g x 1000= 350mg
Table 2: The mass of aspirin in the tablet found by the whole
class.
Mass of aspirin in the tablet (mg)
350
370
114
86
248
580
445
598
563
602
238
344
598
With the help of the table with all of the values found by each individual student, the average has been calculated to be 395.077mg.
((350+370+114+86+248+580+445+598+563+602+238+344+598))/13 = 395.077mg
Discussion
Using my results and graph, the mass of aspirin in the aspirin tablet was found to be 350mg. The mean value for the mass of aspirin found using all the class results was 395.077mg, which is 45.077mg more than my results have shown. This is fairly close, as some of the results from other students were found to be more than 100mg over the average. The mean of the class was affected by some high results (602mg), but also by some lower results (86mg).The true value of the aspirin was, however, lower than both my result and the class average, as the true value was 300mg. The true value shows the mass of pure aspirin in the tablet and does not include other ingredients, which increase the mass of the whole tablet to 344mg. Other ingredients in the tablet include: lactose, potato starch and talc, which have an overall mass of 44mg (344mg-300mg= 44mg). This makes the percentage of aspirin in the aspirin tablet to be 87.21%.
There were quite a lot of errors and uncertainty in the practical, due to equipment fault and human error. The amount of errors is noticeable in the fact that the mass of the aspirin in the tablet equalled 350mg, despite the actual mass of the whole tablet being only 344mg. This suggests that my result was impossible, as it was higher than the mass of the table. This could have been due to contamination of the equipment, as the beaker or the flask could have contained other substances during the practical. Other errors include mixing the right volumes of diluted aspirin standard solution with the NaOH volume, as the glass pipette was used to transfer between 2-8ml of solutions into the test tubes. Human error could have caused wrong volumes of solution to be added, as the pipette could have contained the wrong volume as the measurement went from bottom to top on the pipette (10ml-0ml), so for 2ml the meniscus would be at 8ml. Another error could be due to air bubbles being stuck at the bottom of the pipette, which would not allow the whole volume to be drawn by the pipette. Another error could include the rinsing of the beaker, and the pestle and mortar, as they could have still had a small amount of the powder left in them, which would have interfered with the results, as the mass would have been different per 100ml, changing the concentration. The volumetric flask which was used for creating the standard solutions was of class B, and the limit for that group is within ±0.1cm3;, as the limit is so small, the uncertainty in this measurement is extremely small. The pipette used was of class A so the uncertainty was also extremely small, as the limit of that group for pipette is ±0.03cm3.
The line of best fit of the graph of absorbance against concentration only goes through one point, which suggests that the results are not extremely accurate since the points do not fit in the straight line.
Conclusion
The mass of the aspirin in the commercial tablet has been found to be 350mg, although the actual mass is only 300mg. This is due to many errors which have been mentioned in the discussion part of this report. The actual mass of the aspirin in the tablet is 300mg, this shows that aspirin makes up 87.21% of the aspirin tablet, and the other 12.88% contains other substances such as lactose, potato starch and talc. Measuring the absorbance of the solutions using a photometer is an effective way of comparing solutions of different concentrations, as it allows a graph to be drawn. This is a fairly quick process, although it needs the person performing the practical to have a full knowledge of how to use the equipment, as it needs to be zeroed (‘0’) before use.