6 - Spectrophotometric Analysis of a Commercial Aspirin Tablet

Spectrophotometric Analysis of a
Commercial Aspirin Tablet

Experiment ( 6 )

Name:
Student no.
Section no.

Exp no. 6

Exp title:

Determination of the molecular mass of metal carbonate by back titration.

Aim:

To determine the % active ingredient chemical of a commercial Aspirin.

Introduction: (Page 34)

Acetyl salicylic acid (ASA) is one of the oldest synthetic drugs. First synthesized in
Germany by the Bayer company and marketed under the name “Aspirin” it has
remained one of the most popular “over the counter” drugs of all time. Its main effect is
as a pain killer and fever depressant, but in addition there is strong evidence that in low
daily dosages it lowers the incidence of heart attacks. In the last few decades other
drugs such as acetaminophen (commercial trade name Panadol, also Tylenol) and
ibuprofen (trade name Advil) have taken much of the market for ASA, but ASA remains
an important and widely used medicine.

Drugs, in addition to their active compound, often contain other inactive ingredients
(called excipients in the pharmaceutical industry) such as binders, fillers, dyes, drying
agents, etc. The content of active ingredient in a tablet will always be stated on the
package. In this experiment we will determine the percent active compound in a
commercial aspirin tablet. Aspirin is the trade name for acetylsalicylic acid (ASA). The
ASA in the tablet will be reacted with Fe3+, forming an intensely violet coloured
complex. The concentration of the complex will be determined by means of
spectrophotometry, using a UV/VIS spectrophotometer. Finally, we will be able to
calculate the weight and the weight% of ASA in the commercial tablet.

Producer: Lab manual page 35.

Data & Results: Absorbance Concentration, M
0.129 nm 0.72×10-4 M
Solution 0.261 nm 2.54×10-4 M
SA1 0.554 nm 4.71×10-4 M
SA2 0.970 nm 6.52×10-4 M
SA3
SA4

Absorbance Absorbance Vs. Concentration

1.00 7
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00

0123456
Concentration ×10-4 (M)

Calculation:

1. Mass of aspirin tablet = 0.13 g
2. Absorbance of “ASA unknown” = 0.258

3. Concentration of ASA UNKNOWN as a determined from the

calibration curve:

CASA UNKNOWN = 2.2×10-4 mol/L
4. Concentration of “stock ASA unknown”,

CSTOCK ASA UNKNOWN = (50.0/2.00) × CASA UNKNOWN =
= (50.0/2.00) × 2.2×10-4 = 5.5×10-3 mol/L

5. Moles of ASA in 100mL solution

= Concentration of “stock ASA unknown” = 5.5×10−3 = 5.5×10-4 mol

10 10

6. Mass of ASA:

= mol × MM = 5.5×10-4 × 180 = 0.099 g

7. % of ASA in aspirin :

= Mass of ASA ×100 = 0.099 ×100 = 76.15 %
Mass of aspirin tablet 0.13

Discussion:

In part one of this experiment, we measured four different volumes of salicylic acid
solution into four test tubes, then we filled them up to 10mL using FeCl3. We had
different colors of the solutions. We found the concentration of the unknown by the
calibration curve which was 2.2×10-4 mol/L.

In the second part, we weighted the aspirin tablet, 0.13g then we added NaOH, and
dissolved it on a hot plate. We decanted the liquid to a 100 mL volumetric flask, after
that we filled the flask with FeCl3. The presence of binders and filters in the tablet made
the solution cloudy but that dissapered when we added the Fe+3 solution. The
absorbance of the solution was 0.258, and the concentration is 5.5×10-3.

There was some expected errors in this experiment such as:

- Error in weighting the amount of the chemicals.
- Error in the measurement.
- The aspirin tablet was not dissolved correctly.
- We had undissolved material in the solution.
- We might had some errors in diluting the stock ASA solution because the amount

of water we added was above the line.

Conclusion:

In this experiment, we determined the % of active ingredient chemical of commercial
Aspirin, and it was 76.15 %.