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Analysis of Aspirin Tablets Assessment: (A/I) Introduction: Aspirin is an analgesic and antipyretic drug. The main constituent of aspirin tablets is an organic acid. Objective: The object of this experiment is to determine the percentage of 2-ethanoylhydroxybenzoic acid (acetylsalicylic acid) in aspirin tablets. A known amount of standard sodium hydroxide solution is used in excess to hydrolyze a known mass of aspirin tablets. CH3COOC6H4COOH + 2NaOH
CH3COONa + HOC6H4COONa + H20
The unused sodium hydroxide which remains is then titrated with standard acid. The amount of alkali required for the hydrolysis can then be calculated, using the above equation. The amount in moles of the acid which has been hydrolyzed can be found. This method can be described as performing a "Back Titration." Materials and Apparatus 1.
Chemicals 1. 1 M sodium Hydroxide 2. 0.1 M Hydrochloric acid 3.
Phenolphthalein Indicator (dropper Bottles)
4. Aspirin Tablets 5. Distilled Water 6. Soap Solution.
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Procedure: 1. Finding the total amount of moles of NaOH 1. Standardize the approximately 1.0 M NaOH used for the hydrolysis as follows. a.
Using a pipette filler, pipette exactly 25cm3 of the approximately 1.0 M NaOH solution into a 250 cm 3 standard volumetric flask and make up to the mark with distill water.
b.
Pippette 25cm3 of this solution into a conical flask and put 2-3 drops of phenolphthalein indictator Now titrate it against 0.10 M hydrochloric acid . (See fig. 10a and 10b 11,12)
c.
Carry out one rough titration and two accurate titrations. Record your results. If the two accurate readings does not correspond by less than 0.5 cm3 then do another one until two consecutive results is abtained.
d. (The rough can be determined by pouring the HCl from the burette until the endpoint reaches). Then record at which reading it occurs. e.
Then for the accurate ones, pour some the HCl from the burette into the conical flask until there is a difference of about 5-6 cm 3 from the endpoint (base on the rough titration. Then to reach the end point pour drop wise.
f. Once the titrations are finished, discard the solution from the standard flask. Description Rough First Titration Second Titration Third Titration Average
Initial Reading
Final Reading
Volume of HCl
Table 1 2. Hydrolyze the aspirin as follows. a.
Weigh accurately between 1.3g and 1.7g of the Aspirin tablets into a dry and clean conical flask. Record the mass of aspirin tablets taken. (Remember to press the zero button on the scale so that the weigh of the conical flask is not taken.
b.
Using a safety filler and a pipette, pipette 25cm3 of the approximately 1.0 M NaOH on to the tablets, followed by about the same volume of distilled water.
c.
Simmer the mixture gently for 10 minutes to hydrolyze the acid. Take a typing sheet and fold it lenghtwise for about 4-5 foldings. heat over the flame but do not make
Analysis of Aspirin Tablet
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d.
the flame touches the bottom of the flask. DO NOT BOIL THE SOLUTION OR ELSE YOU NEED TO START OVER. ( See Figure 8b)
e.
Cool the mixture over the faucet and transfer all the solution from conical flask with washings to a 250 cm3 standard flask and make up to the mark with distilled water. [See fig 6 on the lab techniques.]
3. Finding the unused NaOH after the hydrolysis a.
Pipette 25cm3 of the hydrolyzed solution from the standard flask into a conical flask.
b.
Titrate this against 0.10 M hydrochloric acid using phenolphthalein indicator. Put 2-3 drops of Phenolphthalein indicator into the conical flask containing the hydrolyzed solution.
c.
Repeat the experiment for about three times until two consecutive readings is obtain. Record your titration results.
Description Rough First Titration Second Titration Third Titration Average
Initial Reading
Final Reading
Volume of HCl
Table 2 Calculations: 1. Calculate the accurate concentration of the base used. 2. Find the moles of NaOH used in the hydrolysis of the aspirin? 3. Find the moles of the acid hydrolyzed. 4.
Calculate the percentage by mass of the aspirin acid per tablet and your percentage error [325mg of acetylsalicylic acid is present in each tablet theoretically]
5.
Find what percentage of the aspirin tablets is the acid and compare it with the experimental value.
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Discussion: 1.
Why is the mixture simmered gently and carefully during hydrolysis.
2. Why is it not encouraged to boil it vigorously? 3.
Why should the washings be transferred carefully to the 250 cm3 standard flask.
4. Investigate the chemical and methodical principles behind this titration. 5. Identify the acid in question, accompanied by its structure. 6. What mass of the acid is normally found in aspirin tablets? 7. Compare with your results. 8. What may have been some limitations or sources of errors? 9. Discuss, briefly, the use of aspirin as an analgesic and an antipyretic drug. 10. What are the other component/s of aspirin?
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Analysis of Aspirin Tablets Assessment: (A/I) Mark Scheme General Analysis Brief Background Information (Include Definitions of relevant terms) [3] Calculations Accuracy in Calculations
[1]
Choice of Formula/ Relevant Quantities
[1]
Clear/Stepwise
[1]
Correct Units/Significant Figures
[2]
Limitations and Assumptions of Data Percentage Error/ Sources of Error
