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Treatment of Results

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Introduction

Treatment of Results Part 1 Obtaining a calibration plot Salicylic Acid Solution /cm3 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 ...read more.

Middle

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 . ...read more.

Conclusion

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. ...read more.

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