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Lab 8 Report.docx - Lab Report 8 Spectrophotometric...

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Lab Report 8 Spectrophotometric Analysis of Commercial Aspirin Purpose In this experiment, we will use visible spectrophotometer to determine the amount of Acetyl Salicylic Acid (ASA) in mass percentage that is contained in the commercial aspirin tablets. Theory The concentration of ASA can be determined by obtaining the percent transmittance of the ASA solution using a visible spectrophotometer. After the % transmittance is obtained, the absorbance of the analyte in solution may be calculated using the following formula: A = 2 log ( %T ) We will also use the Beer’s Law equation: A = ε ×b× [ c ] In this formula, ε = molar absorptivity of the particular absorbing species in 1/(M.cm), b = path-length of the light through the solution, and [c] = concentration of the absorbing species in moles/L. We will prepare the known and unknown ASA solutions by hydrolyzing the samples in NaOH solution and Fe 3+ ions from the FeCl 3 solution, which will help to bring out the color. We will prepare a series of known concentrations of ASA and read the percent transmission of each standard solution. We will then create a graph of absorbance vs. concentration to obtain a straight line Beer’s Law Plot and the slope (k) of the plot. Considering that k = ε ×b , and c k = A / ¿ ], the concentration of the unknown ASA solution can be calculated using the absorbance of the unknown solution and the slope (k) obtained in the previous step.
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