CM1191 Expt 5 Kinetcs Of Aspirin Hydrolysis
CM1191
Experiment 5 Kinetic Studies on the Decomposition of Aspirin
Aims
To investigate the molar absorptivity of salicylic acid
To determine the concentration of dissolved aspirin in heated water at various times
To determine the effective rate constant of the decomposition of aspirin in heated water at 85°C.
Results and Discussion The molar absorptivity of salicylic acid, ε, can be calculated from the equation, A = εcl. A more accurate value can be obtained by finding the gradient of a graph of absorbance of the iron complex, A, against varying values of c, concentration of salicylic acid. The value of ε is then taken up to be 1226 M-1cm-1. Calculated results and the graph are as shown below:
Table 1: Absorbance against the varying concentrations of Salicylic Acid
Standard Solution c, [salicylic acid] x 10-4/ M
A, Absorbance
1
0.733
0.088
2
1.47
0.180
3
2.20
0.277
4
2.93
0.355
Figure 1: Graph of Absorbance of the Iron Complex, A = εcl
However, there is a point in the graph that slightly deviates above the line of best fit. This may be because of some water leaving from the 3-neck round bottom flask as steam, when different volumes of salicylic acid solution were being pipetted out. This increased the concentration of salicylic acid in that flask, and the value of A obtained would thus be slightly higher than expected.
A possible remedy to this could be to pipette the solution quickly above the 5.0mL marking and stopper the flask immediately after. Next, carefully reduce the solution in the pipette to the 5.0mL marking. This minimizes the time spent needed to obtain exactly 5.0 mL of solution when the 3-neck round bottom flask is left open. Hence, the water loss by steam is further minimized.
By using the values of A measured at different time intervals from the decomposition of aspirin, the corresponding values of [salicylic acid] can be calculated from the equation. Consequently, the values of [aspirin] in the 3-neck round bottom flask and
Experiment 5 Kinetic Studies on the Decomposition of Aspirin
Aims
To investigate the molar absorptivity of salicylic acid
To determine the concentration of dissolved aspirin in heated water at various times
To determine the effective rate constant of the decomposition of aspirin in heated water at 85°C.
Results and Discussion The molar absorptivity of salicylic acid, ε, can be calculated from the equation, A = εcl. A more accurate value can be obtained by finding the gradient of a graph of absorbance of the iron complex, A, against varying values of c, concentration of salicylic acid. The value of ε is then taken up to be 1226 M-1cm-1. Calculated results and the graph are as shown below:
Table 1: Absorbance against the varying concentrations of Salicylic Acid
Standard Solution c, [salicylic acid] x 10-4/ M
A, Absorbance
1
0.733
0.088
2
1.47
0.180
3
2.20
0.277
4
2.93
0.355
Figure 1: Graph of Absorbance of the Iron Complex, A = εcl
However, there is a point in the graph that slightly deviates above the line of best fit. This may be because of some water leaving from the 3-neck round bottom flask as steam, when different volumes of salicylic acid solution were being pipetted out. This increased the concentration of salicylic acid in that flask, and the value of A obtained would thus be slightly higher than expected.
A possible remedy to this could be to pipette the solution quickly above the 5.0mL marking and stopper the flask immediately after. Next, carefully reduce the solution in the pipette to the 5.0mL marking. This minimizes the time spent needed to obtain exactly 5.0 mL of solution when the 3-neck round bottom flask is left open. Hence, the water loss by steam is further minimized.
By using the values of A measured at different time intervals from the decomposition of aspirin, the corresponding values of [salicylic acid] can be calculated from the equation. Consequently, the values of [aspirin] in the 3-neck round bottom flask and