Treatment of Results Essay Example

Treatment of Results Essay Part 1 Obtaining a calibration plot Salicylic Acid Solution /cm3 We will write a custom essay sample on Treatment of Results specifically for you for only $16.38 $13.9/page Order now We will write a custom essay sample on Treatment of Results specifically for you FOR ONLY $16.38 $13.9/page Hire Writer We will write a custom essay sample on Treatment of Results specifically for you FOR ONLY $16.38 $13.9/page Hire Writer Concentration /mol.dm-3 Absorbance A 0.0 0.000 0.002 B 0.5 0.048 0.301 C 1.0 0.096 0.487 D 1.5 0.144 0.715 E 2.0 0.192 0.923 F 2.5 0.240 1.184 To calculate the above concentrations, it is required to use the volumes of salicylic acid as shown above, using the formula below: Concentration = weight of tablet specified on container x volume of salicylic acid solution volume of total solution total volume of standard solution Therefore the concentration for 0.5cm3 salicylic acid solution is: = 300 x 0.5 250 12.5 = 0.048 mol.dm-3 These steps are repeated to calculate the other concentrations, each time changing the volume of salicylic acid solution used. Calculating the least squares regression line xi yi xi-x (xi-x)2 yi-y (yi-y)2 (xi-x)(yi-y) 1 0.000 0.002 -0.12 0.0144 -0.60 0.3600 0.0720 2 0.048 0.301 -0.072 0.0052 -0.55 0.3069 0.0399 3 0.096 0.487 -0.024 0.0006 -0.12 0.0132 0.0028 4 0.144 0.715 0.024 0.0006 0.11 0.0128 0.0027 5 0.192 0.923 0.072 0.0052 0.32 0.1030 0.0231 6 0.240 1.184 0.12 0.0144 0.58 0.3387 0.0698 0.72 3.612 0 0.0403 -0.25 1.1347 0.2103 x = 0.72 = 0.12 6 y = 3.612 = 0.602 6 The equation for the least squares regression is in the algebraic form: y = a + bx where a is the intercept of the line on the y-axis and b is the slope of the line. [1] [2] b = 0.2103 = 5.2184 0.0403 a = 0.602 (5.2184 x 0.12) = -0.0242 Therefore the equation for the least squares regression line is: y = 5.2184x 0.0242 Part 2 Interference Studies Concentration /mol.dm-3 Absorbance Acetylsalicylate 0.0261 0.154 Salicylamide 0.2204 1.081 Caffeine -0.0056 0.004 Acetaminophen -0.0058 0.002 The table above shows the results obtained for this part of the investigation. It can be seen that caffeine and acetaminophen have a much lower concentration than acetylsalicylate and salicylamide which suggests that these two compounds are not present in the aspirin. However, with previous knowledge, we know that acetylsalicylate and salicylamide are present in aspirin, which explains a higher concentration than the other two compounds. Part 3 Optimisation of the conditions for the hydrolysis of acetylsalicylate Time /sec Concentration /mol.dm-3 30 0.2075 130 0.2125 230 0.4511 330 0.3535 430 0.1922 530 0.2068 630 0.2142 730 0.2045 830 0.2178 930 0.2285 The results obtained above shows the reaction time for the amount of salicylate formed for ten minutes. Referring to the graph, it can be seen that there is a relatively linear relationship which suggests that the reaction may have completed by the time the absorbances were measured. The first reading was taken at 30 seconds and every minute thereafter. Another reason for the linear relationship could also be that the reaction taking place is very fast and we were unable to measure the absorbances at the initial rate. Part 4 The assay of the aspirin content of a tablet Concentration /mol.dm-3 Absorbance 1 0.1581 0.784 2 0.1342 0.670 3 0.1603 0.795 Calculating the w/w% aspirin in the tablet Weight of aspirin = highest concentration of salicylic acid solution x dilution factor x total volume of solution (dm-3) Dilution factor = total volume . volume of salicylic acid solution used Therefore: Weight of aspirin = 0.2400 x 12.5 x 250 2.5 1000 = 0.3g Therefore w% of aspirin = weight of aspirin x 100 weight of tablet = 0.3 . x 100 0.3352 = 89.4% Calculating the 95% confidence interval [1] where à ¯Ã‚ ¿Ã‚ ½ is the true mean, x is the measured mean, s is the measured standard deviation, n is the number of measurements and t is the value from the Students t table xi xi-x (xi-x)2 1 0.1581 0.0072 0.00005184 2 0.1342 -0.0167 0.00027889 3 0.1603 0.0094 0.00008836 0.4526 0 0.00041909 x = 0.4526 = 0.1509 3 s = ?(xi-x)2 = 0.00041909 = 0.0145 n 1 2 t = 4.303 n = 3 Therefore: à ¯Ã‚ ¿Ã‚ ½ = 0.1509 à ¯Ã‚ ¿Ã‚ ½ (4.303 x 0.0145) V3 à ¯Ã‚ ¿Ã‚ ½ = 0.1509 à ¯Ã‚ ¿Ã‚ ½ 0.0360g From this we can now compare the result for the weight of aspirin with the amount specified on the container. The amount specified on the container is 0.3g. However, the result for the weight of aspirin that we obtained is also 0.3g. This suggests we were able to collect all the aspirin that is found in the tablet. Discussion Although there are many parts to carrying out the assay, there are main points that should be considered whilst implementing the procedure. 1 Ensure that all the compounds that required weighing are transferred to the beaker without any spillage. Ensure that no powder or solution is lost during the experiment as this can affect the final result of the purity of aspirin in the tablet. 2 Due to the problem of measuring the absorbance of the required solutions, ensure to minimise the delay of measuring the absorbances of the solutions and to avoid keeping samples in direct sunlight, as this can affect the absorbance of the solution. Limitations General limitations that may have occurred during the experiment could be: 1 Human errors not transferring all the powdered tablet to the beaker. Although we received a high value for the w/w% aspirin in the tablet, some powdered tablet may have been lost whilst transference. 2 Not measuring the absorbances of the solution as quickly as possible. Sunlight could have affected the variation of results we had obtained. 3 Not withdrawing aliquots of solution at regular intervals. This served to be a major problem for part 3 of the investigation as we were unable to collect results for the initial rate of the reaction. The graph shows that the reaction had completed by the first minute of the reaction had ended.