# ANALYSIS OF ASPIRIN BY BACK TITRATION

Angela Cofre                                             Page              20/06/2007

### HNC APPLIED SCIENCE

ANGELA COFRE

14 DECEMBER 2006

Analysis of Aspirin by Back Titration

SUMMARY

The purpose of the experiment was to determine the amount of aspirin in a tablet and to compare this with the amount specified on the label.  The amount of aspirin calculated from the results obtained from titrimetric analysis to be 317 mg. The stated dose of the tablets on the manufactures label was 300 mg

KEY WORDS

Aspirin

Back Titration

Manufactures Labelling

AIMS AND OBJECTIVES

Objectives

The objectives of this experiment are to determine the amount aspirin in a tablet and to compare this with the amount specified on the label. This was carried out using back titration.

Aims

The aims of the experiment were as follows:

• Calculate the number of moles of HCL used in the reaction.
• To determine the amount aspirin in an aspirin tablet and compare it with the amount specified on the label.
• Calculate the number of moles of NaOH taken for hydrolysis.
• Calculate the number of moles of NaOH used in hydrolysis.
• Calculate the number of moles of aspirin.

INTRODUCTION

Aspirin is an acid and can be determined analytically by the method of back titration.

However aspirin is not soluble in water so cannot be titrated directly with an alkali.

So the aspirin is reacted with an excess of sodium hydroxide, which produces a water soluble salt of aspirin.

(The ester group also reacts, so two moles of sodium hydroxide are required to react with one mole of aspirin.)

The excess alkali (which was left over from the above reaction) may then be determined by titration

HCl        +          NaOH                          NaCl              H2O

The amount of alkali which is used up in the initial reaction with aspirin may be calculated, and this can be related to the quantity of aspirin.

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#### Here's what a teacher thought of this essay

Overall this is a four star piece of work. It has an excellent introduction and plan but they could be in a better order to make it easier to understand as back titration can be hard to explain. Good set of results but there was an error in the first calculation which got carried over. Otherwise it is a good piece of work which shows all steps of the calculations clearly. Good analysis of results and suggestions for error given. Improvements would be to include a prediction and some more safety precautions. Good understanding overall.