NALY LYSI SIS S OF ACETYLSALICYLIC ACID QUANTITATIVE ANA T ABLETS BY B ACK -T -TITRATION
IN
ASPIRIN
S.A.P S.A.P.. S AAVEDRA M.C.Z. Z. PORTEZA3 AAVEDRA1, J . C . V ILLASIS2, J.T. LIM2 AND M.C. 1 NSTITUTE OF P HYSICS HYSICS , C OLLEGE OLLEGE OF S CIENCE CIENCE N ATIONAL I NSTITUTE 2 DEPARTMENT OF F OOD , C OLLEGE E CONOMICS OOD S CIENCE CIENCE AND N UTRITION UTRITION OLLEGE OF H OME OME E CONOMICS 3 INING , M ETALLURGICAL ETALLURGICAL AND M ATERIALS E NGINEERING NGINEERING , C OLLEGE OLLEGE OF E NGINEERING NGINEERING DEPARTMENT OF M INING NIVERSITY OF THE P HILIPPINES HILIPPINES ITY , P HILIPPINES HILIPPINES U NIVERSITY , DILIMAN , Q UEZON C ITY DATE PERFORMED : JUNE 22, 2016 INSTRUCTOR ’S NAME: GARRERO, M.J. M.J.
1. Discu Discuss ss the use use of a more more dilute dilute NaOH NaOH solu soluti tion on for for the the stan standa dard rdiz izat atio ion n of NaOH. NaOH solution is very much concentrated compared to the KHP standard. If the 1.0 M NaOH NaOH soluti solution on is used used for standa standardiz rdizati ation, on, very little volume of the solution will be used in the titrat titratio ion, n, making making the data data imprec imprecise ise.. Diluti Diluting ng NaOH NaOH will will increa increase se the volume volume of NaOH used for titration, titration, and thus increases increases 1 precision . 2. Exp Explain ain the the rati ation onal ale e beh behind the the dilution dilution and aliquoti aliquoting ng of the aspirin sample. Dilutio ilution n and and aliq aliquo uoti ting ng of the the aspir aspirin in sample sample is done so that lesser volume volume of excess excess NaOH aOH is need needed ed for for neut neutra rali liza zati tion on and and consequently, lesser volume of HCl for backtitra titratio tion. n. The The aliqu aliquot ot sample sampless are are used used for replicates and will serve as representative for the aspirin aspirin sample 2. 3. Discu Discuss ss the princ princip iples les behind behind the use of back back titr titrat atio ion n in the the anal analys ysis is of aspirin tablets.
Aspi Aspiri rin n is a weak weak acid acid that that unde underg rgoe oess hydr hydrol olys ysis is in a twotwo-st step ep reac reacti tion on:: a fast fast 3 reaction reaction then a slow one . The slow reaction makes it unfavorable for direct titration, thus, back-titra back-titration tion method method is used. Known amount of excess NaOH is added to the aspirin sample to overcome the slow rea reaction tion and the then hea heated ted to spe speed up hydrol hydrolysi ysis. s. Unreac Unreacted ted,, excess excess NaOH NaOH is then then determined through back-titration using HCl stand standar ard. d. Quan Quanti tity ty of NaOH aOH that that actu actual ally ly reacte reacted d with with aspiri aspirin n is now determ determine ined d as well well as amount amount of aspiri aspirin n sample sample,, throug through h stoichiome stoichiometric tric and volumetri volumetricc calculatio calculations. ns. 4. What What is the the impor importanc tance e of simmer simmering ing the tablet in the NaOH solution for 20 minutes. The aspirin, degraded into its component acids (acetic acid and salicylic acid), acid), is reacted to the excess excess NaOH NaOH soluti solution. on. Simme Simmerin ring g is done done to spee speed d up hydr hydrol olys ysis is of the the acid acidss formed. It also makes sure that all acids have been neutralized to completion.
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5. Discuss the possible sources of errors and their effect on calculated parameters The possible sources of error throughout the experiment and their effect on calculated parameters are discussed in Table 1 below. TABLE 1. Possible Sources of Errors and its Effect on Calculated Parameters Source of Error Errors in weighing, standardization
Parameter and Error
Having lower molarity during standardization will lead to higher %ASA. Errors in weighing aspirin sample resulting in lower mass will also result in higher %ASA. Incomplete Fewer acids will react with hydrolysis of NaOH, having more excess aspirin sample NaOH during back-titration. %ASA calculated will be less than the actual value of ASA present in aspirin sample. NonAliquot of the diluted homogeneity of aspirin sample must be aliquot sample homogenous in order to obtain accurate data 2 . Nonhomogeneity due to impurities will cause higher %ASA obtained than actual value. Over-titration Volume of HCl titrant added will be greater than actual volume needed. This will consequently lead to calculations of higher molar concentration for excess NaOH, leading to lower %ASA than actual value.
REFERENCES [1] Abrash, S. A. Chem 141 Titration Lab Lecture Notes. Dr. Samuel A. Abrash. https://facultystaff.richmond.edu/~sabra sh/141Lab/Chem_141_Titration_Lab_Lect ure_Notes_F10.pdf (accessed June 26, 2016). [2] Harris, D. C. Sample Preparation. In Quantitative Chemical Analysis, 7th ed.; W. H. Freeman and Company: New York, 2007; pp 8, 645. [3] Christian, G. D.; Dasgupta, P. K.; Schug, K. A. Experiment 9 Determination of Aspirin Using Back Titration. In Analytical Chemistry, 7th ed.; John Wiley : New Jersey, 2014; pp E16-E18.
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