ANALYSING ASPIRIN TABLETSAIM: To determine the percentage of 2-ethanolhydroxybenzoic acid (acetylsalicylic acid) in aspirin tablets.

BACKGROUND INFORMATION: Aspirin is an analgesic and antipyretic drug that is used to relieve pain and lower body temperature. The main constituent of aspirin tablet is 2-ethanolhydroxybenzoic acid. The alkaline juices in the intestines hydrolyze aspirin to ethanoate ions and 2-hydroxybenzoate ions.

CH3COOC6H4COOH + 2OH- CH3COO- + HOC6H4COO- + H2O

DATA COLLECTION:

Titration 1: NaOH vs. HCl

Trial 1 Trial 2 Trial 3Initial burette reading 0.0 0.0 0.0Final burette reading 35.0 35.3 34.6Volume of 0.1 mol/dm3 HCl added in cm3

35.0 35.3 34.6

Volume of NaOH 25.0 25.0 25.0

Titration 2: Hydrolyzed aspirin - NaOH solution vs. HCl

Trial 1 Trial 2 Trial 3Initial burette reading 0.0 0.0 0.0Final burette reading 13.5 14.0 12.8Volume of 0.1 mol/dm3 HCl added in cm3

13.5 14.0 12.8

Volume of hydrolyzed solution

25.0 25.0 25.0

Mass of aspirin tablets used to make the hydrolyzed solution = 1.63g

Indicator used for the titration was phenolphthalein.

DATA PROCESSING:

Titration 1: NaOH vs. HCl

Trial 1 Trial 2 Trial 3 Average valueInitial burette reading

0.0 0.0 0.0 0.0

Final burette reading

35.0 35.3 34.6 34.97

Volume of 0.1 mol/dm3 HCl added in cm3

35.0 35.3 34.6 34.97

Volume of NaOH 25.0 25.0 25.0 25.0

Titration 2: Hydrolyzed aspirin - NaOH solution vs. HCl

Trial 1 Trial 2 Trial 3 Average valueInitial burette reading

0.0 0.0 0.0 0.0

Final burette reading

13.5 14.0 12.8 13.43

Volume of 0.1 mol/dm3 HCl added in cm3

13.5 14.0 12.8 13.43

Volume of hydrolyzed solution

25.0 25.0 25.0 25.0

To determine the number of moles of NaOH added to flask before hydrolysis of the aspirin, the formula used is –

Number of moles = concentration x volume

Concentration of NaOH used = 1.0 mol/dm3

Volume of NaOH used = 25 cm3 or 0.025 dm3

Number of moles of NaOH = 0.025 moles.

To determine the number of moles of NaOH used in the hydrolyisis of aspirin the formula used is –

CH3COOC6H4COOH + 2NaOH CH3COONa + HOC6H4COONa + H2O

Mass of CH3COOC6H4COOH = 1.63g

Molar mass of CH3COOC6H4COOH = 180 g

Number of moles of CH3COOC6H4COOH = (Mass of CH3COOC6H4COOH)/( Molar mass of CH3COOC6H4COOH)= 1.63/180 = 0.0009 moles

For 1 mole of CH3COOC6H4COOH , 2 moles NaOH are needed

Therefore for 0.0009 mole of CH3COOC6H4COOH, 0.0018 mole of NaOH is needed.

To determine the number of moles of NaOH that remain after the hydrolysis of the aspirin, the formula used is –

Number of moles of NaOH added to flask before hydrolysis of the aspirin - number of moles of NaOH used in the hydrolysis of aspirin

Number of moles of NaOH added to flask before hydrolysis of the aspirin = 0.025 moles.

Number of moles of NaOH used in the hydrolysis of aspirin = 0.0018 mole

number of moles of NaOH that remain after the hydrolysis of the aspirin = 0.025 moles - 0.0018 mole = 0.0232 mole

It is already known, from the prior calculations that the number of moles acetylsalicylic acid used are = 0.0009 moles

To determine the percentage of acetylsalicylic acid in the aspirin tablet, the formula used is –

((Number of mole of acetylsalicylic acid) / (total number of moles))x 100

Number of moles acetylsalicylic acid used are = 0.0009 moles

Total number of moles = 0.0009 moles + 0.0018 mole = 0.0027 mole

Percentage of acetylsalicylic acid in the aspirin tablet = (0.0009/0.0027)x100=33.33%

CONCLUSION:

EVALUATION OF THE PROCEDURE:

There could be few errors because of the difference in the experimental value and the literature value of the percentage of acetylsalicylic acid present in aspirin.

Some of these could be –

The parallax errors that are caused by the error in reading.