Introduction:

Aspirin is an analgesic and antipyretic drug. Analgesics are drugs which relieve pain. Antipyretics are drugs which lower body temperature.

The main constituent of aspirin tablets is 2-ethanoyloxybenzoic acid. Aspirin passes unchanged through the acidic condition and the stomach but is hydrolysed to ethanoate ions and 2-hydroxybenzoate ions by the alkaline juices in the intestines.

CH3COOC6H4COOH   +   2OHֿ   →   CH3COOֿ   +   HOC6H4COOֿ   +     H2O

Salicylates lower body temperature rapidly and effectively in feverish patients, but have little effect if the temperature is normal. They are also mild analgesics, relieving certain type of pains, such as headaches and rheumatism.

Although the toxic dose from salicylates is relatively large, their uncontrolled use could be dangerous. Single dose of 5 to 10 grams of salicylates have caused death in adults, and 12 grams taken over a period of twenty-four hours produces symptoms of poisoning.


Principle:
The object of this experiment is to determine the percentage of 2-ethanoyloxybenzoic acid in aspirin tablets. A known amount of standard sodium hydroxide solution is used in excess to hydrolyze known mass of aspirin tablets.

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CH3COOC6H4COOH   +   2NaOH   →   CH3COONa   +   HOC6H4COONa   +     H2O

The unused sodium hydroxide which remains is then titrated with standard acid. The amount of alkaline required for the hydrolysis can now be calculated and from the above equation, the number of moles of acetylsalicylic acid which have been hydrolyzed can be found.

Requirements:

Aspirin tablets (about 3), 25cm³ pipette, pipette filler

Burette and stand, small beaker

250 cm³ volumetric flask, 250 cm³ conical flask

Filter funnel, Bunsen burner

Tripod and gauze

Procedure:

Part 1 : Standardize the approximately 1M ...

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