Aspirin Titration

ABSTRACT Back titration is a type of titration method wherein the concentration of an analyte by reacting it with a known amount of excess reagent is determined. The left excess reagent is then titrated with a second reagent. Back titrations are used when: one of the reactants is volatile; an acid or a base is an insoluble salt; and the endpoint of hard to observe. The experiment aims to develop techniques on dilution of a solution in a specific volume and manage calculations involving back-titration. The preparation and standardization of 0.1 N HCl solution will be preceded and will be diluted with a standard NaOH used on from the previous experiment until a faint pink appeared after indicator on three trials. An analysis of aspirin will be executed. In relation with this, the hydrolyzed aspirin solution will be titrated with the use of standardized HCl solution and titrating it with 2-3 drops of phenolphthalein Keywords: Back titration, excess reagent, dilution, standardization, 0.1 N HCl, NaOH, faint pink, 2-3 drops phenolphthalein RESULTS Concentration of NaOH: 0.0927 N = 0.0927 M Table 1 Volume of HCl Trial 1 Trial 2 25 mL 25 mL

Trial 3 25 mL

*Table 1 shows the volume HCl that was titrated for the standardization of HCl

Table 2 Volume of NaOH used in HCl Volume of Trial 1 Trial 2 NaOH (in mL) (in mL) Initial 1.4 22.9 Final 22.9 46.2 Used 21.5 23.3

Trial 3 (in mL) 13.1 33.9 20.8

*Table 2 shows the volume of NaOH used to titrate 25 mL HCl

Mass of Aspirin: 0.1074 g Table 3 Aliquot of Aspirin Trial 1 Trial 2 50 mL 50 mL

Trial 3 50 mL

*Table 3 shows the aliquot volume of the ground aspirin to be titrated with the standardized HCl

Table 4 Volume of HCl used in Aspirin Volume of Trial 1 Trial 2 HCl (in mL) (in mL) Initial 13.1 15.5 Final 15.5 17.2 Used 2.4 1.7

Trial 3 (in mL) 17.2 20.4 3.2

*Table 4 shows the volume of HCl that was used in the titration of the ground aspirin

DISCUSSION Aspirin (HC9H7O4, 180.15742 g/mol ) also known as Acetylsalicylic acid, is a type of salicylate acid.It is a kind o drug wherein it reduces substances in the body that experience pain, soreness, and fever. Aspirin or ASA has been used for treatment of rheumatoid arthritis, rheumatic fever, and mild infection. At some instances, it used to cure and prevent heart attacks, strokes, and chest pains. It is commonly used for regulating cardiovascular conditions with the recommendation of a medical psychiatrist. It is composed of white, crystalline, weakly acidic substance. Correspondingly, it has a melting point of 137 ̊C. Moreover, Aspirin is similar to Acetic acid, HC2H3O2 (I) which reacts with strong bases such as Sodium Hydroxide. The experiment is divided into two parts: (a) preparation and standardization of 0.1N of HCl solution and (b) determination of Acetylsalicylic acid (ASA) in aspirin. In the preparation of the standardized 0.1N HCl, an 8.3 mL of 12 M HCl was mixed with water to have 100mL of 0.1 N HCl. It was then standardized with NaOH.Prior to the experiment, the NaOH solution was already standardized. Table 1 and Table 2 shows the volume of HCl and NaOH used. The standardized HCl was then used in the analysis of the aspirin. A 0.1074 gram of aspirin sample was pounded and a 20.00 mL of standardized NaOH was added to it. The mixture was then boiled for 10-15 minutes. It was done in order to hydrolyze the aspirin sample. The experiment involved three trials for the analysis of the aspirin. After the mixture has been cooled, it was then transferred to a 250 mL volumetric flask. It was then washed and diluted until it was filled to the mark. The hydrolyzed aspirin was then titrated with standardized HCl using a phenolphthalein indicator. Table 3 and 4 illustrate the aliquot of the aspirin and the HCl used. The calculations involved in the experiment were: number of moles of NaOH used; the mole of excess NaOH; and the concentration of Acetylsalicylic acid. The formula for calculating the moles of NaOH used was the molarity of NaOH was 0.0927 M and its volume for every trial as shown in Table 2.The computed moles per trial were 1.99 x 10-3 mol, 2.16 x 10-3 mol, and 1.93 x 10-3 mol of NaOH respectively. Furthermore, the mole of excess NaOH was computed by multiplying the molarity of HCl by the volume of HCl used. The molarity of HCl was given as 0.1 M and the volume for every trial was given in Table 4. The calculated results were 2.4 x 10-4 mol, 1.7 x 10-4 mol, and 3.2 x 10-4 mol for first, second and third trial respectively. Lastly, one of the main objectives of this experiment was to determine the concentration of the acetylsalicylic acid in the aspirin tablet. The computed number of moles of the acetyl salicylic acid in the aspirin was 8.92 x 10-4 mol. CONCLUSION The back titration process was properly executed and introduced. Moreover, the objectives of the experiment were successfully met. It was also observed that the volume of NaOH used to titrate HCl along with the volume of HCl used to titrate aspitin does not have a significant difference. The number of moles of Aspirin computed was 8.92 x 104 mol. References: http://www.ausetute.com.au/backtitration.html

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