Determine the percent aspirin in an aspirin tablet and to compare this with the amount specified on the label.
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Titrimetric Analysis of Aspirin Name: Andrew Holmes Student Number: 2103086 Course: BSc Forensic Science Year: 1 Unit: Introduction to Forensic Chemistry Date: 18/03/02 Summary The purpose of the experiment was to determine the percentage of acetyl salicylic acid in an aspirin tablet and to compare this with the amount specified on the label. The average weight of one tablet before titration was found to be 328 mg. The amount of aspirin calculated from the results obtained from titrimetric analysis to be 317 mg. The stated dose of the tablets was 300 mg The percent purity of an aspirin tablet to the amount specified on the label was then calculated to be 96.47 % pure. Aims and Objectives Objectives The objectives of this experiment are to determine the percent aspirin in an aspirin tablet and to compare this with the amount specified on the label. This is carried out using an acid - base titration. Aims The aims of the experiment were as follows: * Calculate the weight of one aspirin tablet. * Calculate the molarity of diluted and stock NaOH solutions. * Calculate the no. Of moles used in hydrolysis. * To determine the percent aspirin in an aspirin tablet and compare it with the amount specified on the label.
25 cm3 of the hydrolysed solution is pipetted into a clean conical flask. 15 drops of phenolphthalein was added to act as an indicator. The solution was then titrated with standard 0.1 mol dm-3 hydrochloric acid. The hydrochloric acid is then released from the burette slowly ensuring the hydrolysed solution is mixed constantly. The starting point of the hydrochloric acid in the burette must be recorded before the titration can begin. The end point is reached when the pink colouring of the indicator is reduced so it is a clear liquid. The titrations are repeated until the titration data is reproducible. The apparatus must be cleaned and dried after each titration to ensure accurate results are achieved. Serval safty precautions must also be practiced. A lab coat must be worn at all times during the lab and long hair tied back. Also safety goggles must be worn when heating the acetyl salicylic acid and the sodium hydroxide. Results 1. Standardisation of 25cm3 sodium hydroxide solution. Burette Readings Initial Reading (cm3) Final Reading (cm3) Volume Used (cm3) Titration 1 1.30 27.40 26.10 Titration 2 1.60 26.00 24.40 Titration 3 0.70 25.15 24.45 Average volume of 0.1 mol dm-3 hydrochloric acid used = 24.98 2 d.p 2. Label information for the aspirin.
* The number of moles of sodium hydroxide used in hydrolysis can be calculated by subtracting the number of moles of sodium hydroxide taken for hydrolysis by the number of moles of sodium hydroxide remaining after hydrolysis. * The weight of one aspirin tablet was calculated by working out the molecular weight of aspirin and multiplying it by the number of moles of aspirin used, to find the weight of the sample of aspirin used in the experiment; and then dividing it by the number of tablets in the sample. * In an acid-base titration, as a strong acid is gradually added to a strong base, it reacts with the base and the pH gradually falls. * Accuracy and precision of the measurements taken in the experiment can influence the data obtained. Experimental error in the results may have been due to the use of inaccurate glassware, human error, systematic error in the * Measurements that will influence the calculations made from the data obtained, glassware not properly rinsed and dried before use, dirt and air on the analytical balance, or the acetyl salicylic acid not fully hydrolysed. * The correct safety precautions were adhered to during experimentation. These included handling glassware in a careful and appropriate manner, wearing safety goggles during the heating stage of the experiment, and using tongs and a heatproof mat.
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