Analysis of Commercial Aspirin Tablets

No.4 Analysis of Commercial Aspirin Tablets

Aims

To To determine the mass of acetylsalicylic acid per tablet in a given commercial sample of aspirn (Brand name).

Introduction

Aspirn, which is chemically named as acetylsalicylic acid, when is hydrolyzed by excess sodium hydroxide solution, produces acetic acid and salicylic acid. The amount of excess sodium hydroxide solution can be found by back titration.

Procedure

Standardisation of sodium hydroxide solution
25 cm3 ofApproximately 1M NaOH was pipetted into a 250 cm3 volumetric flask and made up to graduation mark with deionized water. 25 cm3 portion of this solution was titrated against standard 0.05M sulphuric acid with phenol red as indicator. The titration was repeated twice and the result was recorded in a table.

Hydrolysis of aspirn
An aspirn tablet was placed into a 250 cm3 conical flask. 25 cm3 of the standardized 1M NaOH was pipetted into the conical flask and about same volume of deionized water was added into it. Simmering for about 10 to 15 minutes to hydrolyse the aspirin. After the mixture was cooled, it was transferred with washings to a 250 cm3 volumetric flask and made up to the graduation mark.
Analysis of aspirin
25 cm3 portions of the solution obtained in procedure (2) was titrated using standard 0.05M sulphuric acid with phenol red as indicator. ...

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Hydrolysis of aspirn
An aspirn tablet was placed into a 250 cm3 conical flask. 25 cm3 of the standardized 1M NaOH was pipetted into the conical flask and about same volume of deionized water was added into it. Simmering for about 10 to 15 minutes to hydrolyse the aspirin. After the mixture was cooled, it was transferred with washings to a 250 cm3 volumetric flask and made up to the graduation mark.
Analysis of aspirin
25 cm3 portions of the solution obtained in procedure (2) was titrated using standard 0.05M sulphuric acid with phenol red as indicator. The titration was repeated twice and data obtained was drawn into a table.

Results

Calculation

The initial no. of moles of NaOH before hydrolysis = 1.00M*25cm3*1/1000
=0.025mol
The no. of moles of NaOH left after hydrolysis =0.05M*18.88 cm3*2*1/1000*10
=0.019mol
The no. of moles of NaOH used in hydrolysis =0.025mol – 0.019mol
=0.006mol
The no. of moles of acetylsalicylic acid =0.006mol*1/2
=0.003mol
The mass of acetylsalicylic acid =0.006mol*180g mol-1*1/2
=0.54g

Conclusion

The no of mole and mass of of acetylaslicylic acid present in one tablet of the commercial sample are 0.003mol and 0.54g respectively.

Discussion

Summary of Main Result
The no. of moles of NaOH before hydrolysis was found to be 0.025mol. The no. of moles of NaOH left after hydrolysis was found to be 0.019mol. By subtracting 0.019mol from 0.025mol, the no. of moles of NaOH used in hydrolysis was 0.006mol. Since the mole ratio of NaOH to acetylaslicylic acid is 2:1, so no. of moles of acetylaslicylic acid was 0.006mol*1/2= 0.003mol. Thus, the mass of acetylaslicylic acid was 0.003/180g mol-1 = 0.54g.

Errors
Human error
- Instruments have their width of markings. The reading observed by experimenters will be affected by the width of markings .
- When the reading level seems to be in the middle of two succesive markings, there is uncertainty that whether it should be read as the lower marking or the higher marking.
- Evaporation of water from solution in volumetric flask before stopper is put on.
Comparison between calculated values and literature values

Defects and Improvements
Defect 1:
-some of the aspirin didn’t ionize in solution, only the no. of moles of and the mass of those which were ionized and hydrolyzed can be found. So the calculated value of the no. of moles of and mass of aspirin was smaller than the actual ones.
Improvement:
Grand the aspirin tablet and dissolve it in a larger volume of solution.
Defect 2:
-The sample of aspirin may not contain acetylsalicylic acid only. Other impurities may react with NaOH. So the calculated value of the no. of mole of the acetylsalicylic acid will be larger than the actual value.
Improvement:
-Choose a brand of tablet which contains acetylsalicylic acid only.
Defect 3:
-There are many kinds of errors occuring in the experiment.
Improvement:
-Carrying out the experiment a few times so as to take the mean values(except the trial).
Further investigation
-Test for impurities in aspirin tablets through determining the melting points of aspirin tablets or thourgh chromatography.

Questions

Standard sodium hydroxide solution cannot be prepared by directly dissolving a known mass of sodium hydroxidee solid into water and making up to a certain volume. Why?
There may be water being locked in hydrated crystals of NaOH.
What was the purpose of simmering the reaction mixture during the hydrolysis of the aspirin tablets?
To provide a suitable temperature for the hydrolysis of aspirin to take place.
Suggest an alternative to aspirin which can work without simmering the reaction mixture.
Direct titration with alkali. As the solution of aspirin in flask is buried in ice for prevention of hydrolysis with alkali, simmering is surely not needed.
On what basis would you choose from a variety of brand names when you need this medicine.
The concentration of aspirin contained in the medicines. Whether any gas will be produced when aspirin undergoes reactions in our bodies. What are the side effects caused by these medicines.