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The analysis of aspirin Essay

ANALYSIS OF ASPIRIN TABLETS
The aim of this investigation is to determine the percentage by mass of aspirin aspirin present in different commercial preparations and to find out, which the best value is, using a neutralization reaction followed by a direct titration with NaOH. Chemicals Used:

100 ml of distilled water in a wash bottle
50 ml of 0.100 M NaOH
40 mL of 96% ethanol
phenolphthalein as an indicator (3 drops per titration)
325 mg non buffered aspirin tablets

Materials Used:
One spatula
Two Erlenmeyer flasks, 250 ml
One weighing scale (with uncertainly +-0.005g)
1000 ml graduated cylinder
Buret
One metal stand
Buret clamp
50 cm3 conical flask
Procedure:
The metal stand was assembled with the buret. The latter one was filled with 0.100 M NaOH to just above the 0.00 mark. There was no bubbles apparent in the burette. One table of aspirin was grinded into a fine powder by using a mortar and pestle. A weighing boat was placed on the balance and tare. The powdered sample was carefully transfered to the weighing boat and the mass was determined. The result was recorded on the data table. The powdered sample was placed into a.Then a 10.0 mL portion of ethyl alcohol was added and swirled. At first it was difficult to dissolve the white powder, even after some period of swirling little amount of solid may be seen at the bottom of the flask. The solutions seemed to be not as transparent as expected. Three drops of the phenolphthalein indicator was put into the 50 cm3 conical flask and the solution was swirling constantly.

.
5. The burette is filled with 0.100M NaOH. Make sure there are no bubbles apparent in the burette. Record the initial volume of the base and the initial volume of the aspirin on the data table. Add 25.0mL of water to the flask.

The titration began after adding a first portion of NaOH in 1.0mL increments while constantly swirling, until the solution turns a very light pink. (The equivalence point is approximately when the solution turned pink from the phenolphthalein). The volume was recorded of the resulting aspirin solution and the volume of NaOH used in the data table.

Data Collection and processing
Direct titration of Aspirin Sample A
Number of trials
Mass, g
(+/-)0.01
Expected amount of aspirin
(g)
(+/-)0.01
Volume of ethanol
(cm3)
(+/-) 0.05
Concentration of NaOH
Volume of NaOH
(+/-)0.1

Trial 1
0.355
0.325
10.0
0.100
17.75
Trial 2
0.361
0.325
10.0
0.100
17.91
Trial 3
0.367
0.325
10.0
0.100
18.49

Direct titration of Aspirin Sample B (Cardio)
Number of trials
Mass, g
(+/-)0.01
Expected amount of aspirin
(g)
(+/-)0.01
Volume of ethanol
(cm3)
(+/-) 0.05
Concentration of NaOH
Volume of NaOH
(+/-)0.1

Trial 1
0.141
0.100
10.0
0.100
6.39
Trial 2
0.136
0.100
10.0
0.100
6.01
Trial 3
0.138
0.100
10.0
0.100
6.19

Qualitative data
The NaOH solution after being used was stored in a open beaker in a unventilated cupboard. During all three trials the flask has been swirling, that caused some minor splashing. Although the titration was conducted until the endpoint when the solution would no longer change color, the resulting color from this method (light pink) was slightly different in depth after the titration.

Calculations
Considering the sample A
Average NaOH used during direct titration of NaOH:

The uncertainty for the value of NaOH used:

Based on the given concentration of NaOH 0.10 mol/dm3 the number of moles is: 0.01805 dm3 × 0.10 mol/dm3 = 1.805×10-3 mole (+- 3.0 %)
The percent uncertainly for the volume of NaOH is determined to be:

Due to one-to-one ratio of the NaOH and aspirin, the amount of aspirin used is the same. Moles of aspirin at endpoint: 1.805×10-3 mole (+- 3.0 %)
The molar mass of aspirin is
M(C9H8O4) = 180.15 g/mole
The Experimental mass of aspirin:
1.805×10-3 mole ×180.15 = 0.325g (+- 3.0 %)
% aspirin in the tablet:

% purity = 0.325/0.355 = 91.55 %

Considering the sample B
Average NaOH used during direct titration of NaOH:

The uncertainty for the value of NaOH used:

Based on the given concentration of NaOH 0.10 mol/dm3 the number of moles is: 0.0062 dm3 × 0.10 mol/dm3 = 6.2×10-4 mole (+- 3.1 %)
The percent uncertainty for the volume of NaOH is determined to be:

Due to one-to-one ratio of the NaOH and aspirin, the amount of aspirin used is the same. Moles of aspirin at endpoint: 6.20×10-4 mole (+- 3.1 %)
The molar mass of aspirin is
M(C9H8O4) = 180.15 g/mole
The Experimental mass of aspirin:
6.20×10-4 mole ×180.15 = 0.112g (+- 3.1 %)
% aspirin in the tablet:

Expected purity, % = 0.112/0.355 = 91.55 %


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