F.6/7 Chemistry Practical: The Analysis of Aspirin Tablets
Objective:
To carry out a consumer survey, that is to analyze the active ingredient in aspirin tablets of different
brands so that we can have the best buy.
Group size: Individual
Introduction
In all pharmaceutical preparations, the manufacturer is required by law to state on the
packaging the maximum amount of each active ingredient present. In many preparations the
active ingredient will only form a small percentage of the pill or tablet as a whole. For example,
in the case of many tablets, the tablet would simply disintegrate into a powder unless additives
were put in to assist in making the ingredients cohere into tablet form.
In this experiment students will have the opportunity to carry out a consumer survey on the
aspirin content of a number of commercial preparations, to see whether the manufacturers claims
are justified.
Aspirin is the commercial name (refer to the active ingredient) of acetylsalicyclic acid. This
acid can be readily hydrolyzed by sodium hydroxide into the sodium salts of two weak acids,
acetic acid [its IUPAC name is ethanoic acid] and salicyclic acid [IUPAC name,
hydroxybenzenecarboxylic acid]. The equation for the hydrolysis reaction is:
----------------------------------------------------------------------------------------------------------------------Theory: Give principle/reason to explain how do you compare two brands of aspirin. The
following questions should be useful to you.
1. What is meant by the term ‘active ingredient’ in a medicine tablet?
2. Which is the active ingredient in aspirin tablet?
3. Give the method to analyse the active ingredient in an aspirin tablet.
4. Calculate the molar mass of the aspirin.
5. How many mole of sodium hydroxide is required to react with 1 mole of aspirin?
6. To react with 0.50 g of aspirin how many moles of sodium hydroxide should be used?
7. Suppose molarity of sodium hydroxide solution and sulphuric acid are M1 and M2 , respectively.
V1 and V2 are volume of sodium hydroxide solution and sulphuric acid. Using these symbols,
express
(a) number of mole of sulphuric(VI) acid used;
(b) number of mole of excess sodium hydroxide;
(c) number of mole of sodium hydroxide reacted with aspirin;
(d) mass of aspirin in the tablet.
--------------------------------------------------------------------------------------------------------------------To facilitate the comparison of content of aspirin in different brands of the medicine, the cost
(HK$) per gram of aspirin should be calculated and you can determine which one is the best buy.
Chemicals:
Aspirin tablet of mass about 1.0 g, 250 cm3 of standardized sodium hydroxide solution (about 1 M),
250 cm3 of standardized sulphuric acid (about 0.05 M), phenol red indicator,
Additional apparatus:
A set of burner, tripod and heat shield, accessible to a balance readable 0.01 g
Procedure
Distilled water may be replaced by de-ionized water. Wear goggle in the course of the practical
Record your results immediately after you get the readings.
1. Weigh accurately a definite number of aspirin tablets (two or three tablets weighing no more
than 1.5 g) by using a weighing bottle or a piece of clean paper.
VA05_aspirin/p.1
2.
Totally transfer the tablet(s) into a 250 cm3 conical flask.
3.
Initiate the hydrolysis of the aspirin by adding 25.0 cm3 of the standardized sodium hydroxide
by pipette, diluting with approximately the same volume of distilled water.
Warm the flask over a tripod and gauze for ten minutes to complete the hydrolysis. [Caution:
Don't boil the solution.]
Cool the reaction mixture and transfer with washings to a 250 cm3 volumetric flask. [Note:
The conical flask must be rinsed for at least two times.]
Dilute to the graduation mark with distilled water and then ensure that the content of the flask
is well mixed by repeated shakings.
Titrate 25.0 cm3 portions of the diluted reaction mixture with the standard 0.05 M sulphuric(VI)
4.
5.
6.
7.
acid provided, using phenol red indicator. Record your data. Try to get two concordant
readings.
8.
Repeat the above steps for aspirin of another brand. Put all your data into the Data section.
Data and Results
Concentration of sodium hydroxide solution: ________________
Concentration of sulphuric(VI) acid: ______________
Weighing data
Brand of the aspirin:_____________ Cost: ________
Mass of aspirin tablet + paper =
Mass of paper
=
Mass of aspirin
=
Colour change of the indicator: _____________________________
Run
1
2
3
Final burette reading/cm
Initial burette reading/cm3
Volume of HCl used/cm3
Average titrant:
Brand of the aspirin:____________ Cost: ________
Mass of aspirin tablet + paper =
Mass of paper
=
Mass of aspirin
=
Titration Data:
Run
1
2
3
Final burette reading/cm
Initial burette reading/cm3
Volume of HCl used/cm3
Average titrant:
3
3
Calculation:
Calculate mass of aspirin in each tablet, then calculate for the cost (HK$) per gramme of aspirin.
Discussion:
1. Give error sources and estimate percentage error for the percentage of active ingredient in the
tablets.
2. Other pH indicator may be suitable for this experiment. Give one example.
3. Give safety precautions for this experiment.
Conclusion: Determine which one is the best buy. Hand in your report to Mr. Lam before 4:30 p.m.
VA05_aspirin/p.2