Chemistry - Titration of Aspirin Tablets

Question # 00801096 Posted By: dr.tony Updated on: 04/06/2021 04:15 AM Due on: 04/06/2021
Subject Education Topic General Education Tutorials:
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Titration of Aspirin Tablets

In this lab, you will determine the amount of acetylsalicylic acid (2-ethanoyloxybenzene carboxylic acid) in a batch of aspirin tablets through a titration simulation. You will do a simulation that guides you through the process step by step learning a variety of techniques. This is a common practice in industries to test the purity of the samples and to see if the amount of acetylsalicylic acid matches the amount on the box. This is called Quality Assurance, random samples from each batch of tablets are tested in a variety of ways to see if they fall within the conditions for use and sale.

To find the amount of acetylsalicylic acid (2-ethanoyloxybenzene carboxylic acid) in the tablets you will be preforming a virtual acid base titration. In general, an acid and a base react to produce a salt and water by transferring a proton (H+).

HA(aq) + NaOH(aq) ?H2O(l) + NaA(aq)

Acid Base Salt With that being said this is the reaction that will be occurring in your titration:

Aspirin (C9H8O4) + Hydroxide


-The circled hydrogen is the proton that is transferred to the hydroxide creating water.

-Aspirin is a weak acid. What does that tell you about how aspirin dissociates and ionizes?

An aspirin tablet may also include inactive ingredients that help produce a consistent product for consumers. Think of the purpose these ingredients serve when considering the amount of acetylsalicylic acid (2-ethanoyloxybenzene carboxylic acid) in the sample you analyze, the possible presence of impurities and the overall size of the tablets.

Before you begin the simulation, we will go through some basics about titrations and the technique. Not all these techniques will be used during the simulation, but are important for you to know for future lab courses and lab work.

What is a titration?


Titrant (in buret)

A titration is a procedure for determining the concentration of a solution (the analyte) by allowing a carefully measured volume of this solution to react with another solution whose concentration is known (the titrant). The point in the titration where enough of the titrant has been added to react exactly with the analyte is called the equivalence point, and occurs when moles of titrant equals moles of analyte according to the balanced equation. For example, if a monoprotic acid (the analyte) is titrated with a strong base like sodium hydroxide (the titrant), the equivalence point occurs when

number of moles of OH- = number of moles of HA.

The equivalence point is often marked by an indicator, a substance that changes color at (or very near) the equivalence point. The equivalence point can also be found with a titration curve. Titration curves are made by putting a pH probe in the analyte and running the reaction until the curve flattens out. Titration curves are plotted on a graph of pH versus the volume of titrant and have a unique s-shape that you can find the equivalence point from. For example see the titration curve of sodium hydroxide and hydrochloric acid.

1) Shows the initial contents of the analyte. In this case water, hydrochloric acid, and the small amount of salt that has begun to form from adding the titrant (NaOH)

2) THIS IS THE EQUIVALENCE POINT. The whole middle is range you would use to find an indicator.

3) Shows the contents of the analyte once you past the equivalence point. The sodium hydroxide is in excess and the hydrochloric acid has dissociated to make sodium chloride.

When the indicator changes color it is called the endpoint, we will normally assume that the endpoint is equal to the equivalence point. There are a variety of different indicators that have different endpoints and we want to choose ones that the range of pHs that it changes color in is around the equivalence point.

There are many types of titrations. In this lab you will be performing an acid base titration.

Laboratory Technique for Burets

Burets are used to deliver a recorded amount of liquid or solution to another container. A buret is marked in milliliters like a graduated cylinder, but buret markings show 0 mL at the top, and the numbers increase as you go down the buret. The stopcock controls the liquid flow. It is open when parallel to the length of the buret and closed when perpendicular to the length of the buret.

· Washing and rinsing the buret: To clean a buret, wash its interior with soap and tap water. Next, rinse the buret with 5-10 mL portions of DI water. With the buret over the sink and the stopcock open, pour the water into the buret and let it drain out the tip. Use a beaker to pour solutions into the buret—most breakage occurs during washing, and burets do NOT fit under the faucet.

· Conditioning the buret: After the buret is well-drained, close the stopcock and add about 5 mL of the titrant (the solution to be used into the buret). Tilt the buret sideways and roll the barrel to completely rinse the inner walls of the buret. Drain the solution through the buret tip to insure the tip is also conditioned. Repeat this step at least twice to be sure all interior surfaces are rinsed with titrant.

· Filling the buret: Close the stopcock. Use a clean funnel to fill the buret with titrant just above the “0” mark. Place a container under the buret tip, and open the stopcock briefly to fill the buret tip with solution, leaving no air bubbles, and to get the level of meniscus to fall within the markings of the buret. If the tip does not fill with solution when the stopcock is in the open position, there may be an air bubble in the stopcock. Consult your instructor.

Note: The initial level of titrant need not be exactly at 0.00 mL as the initial level of liquid will be recorded and subtracted from the final volume to determine the volume delivered.


· Reading the buret: Always remove the funnel used to fill the buret before taking any measurements. Record the volume of titrant by noting the bottom of the meniscus. On the buret shown below, numbers marked for every 1 mL, and the ten lines between each number represent every 0.1 mL. Thus, the level of titrant in the buret can be estimated to one more decimal place than the markings or to the nearest 0.01 mL.


Thus, in the figure to the right, the meniscus is about halfway between 25.0 and 25.1 mL, so the level of titrant can be recorded as 25.04 mL, 25.05 mL, or 25.06 mL depending on whether the bottom of the meniscus appears to be just above, just at, or just below halfway, respectively.

· Cleaning the buret: Afterwards, empty the buret, disposing of the titrant according to the waste disposal instructions for each experiments. Wash the buret with soap and tap water, then rinse with several portions of tap water, allowing some tap water to run through the tip. Do a final rinse with small portions of DI water, allowing the DI water to run through the tip, then return the buret to the stockroom.



1. Follow the link to Royal Chemical Society Website:

2. Choose the Titration option. From there you will be prompted to either Login or ter. Choose “Login” and type the code from your aspirin synthesis. If you lost or forgot your code you can choose “ter” and type in your name. Write down the code on your report sheet.

3. Proceed to select “Level 2” watch the video and answer the questions you are given. Don’t fret about your score just try your best, you are being graded for actually doing the virtual lab, NOT from the score you receive on the simulation.

4. Remember from the last experiment simulation, this website uses the IUPAC names for the organic compounds not the common names. The one you will see the most often is for aspirin, what we have been referring to as acetylsalicylic acid. They use the name 2-ethanoyloxybenzene carboxylic acid.

5. Next you will prepare the tablets for the titration with their drag and drop lab equipment. This requires counting out ten tabs and using a mortar and pestle to crush them. Why are the tablets being crushed before the analyte is made?

6. From here you will mix the analyte with the crushed aspirin to be used during the titration. Follow the instructions to mix the sample. Remember to rinse the beaker, why is this important? Be aware that they are picky about where your meniscus is.

7. Then you will measure out and dispense the analyte for the titration curve. Before using the graduated pipet, you are prompted to rinse it with the analyte. Again why is this important?

8. Transfer the 25mL of analyte to the beaker with the graduated pipet.

9. Next you will prepare your buret as discussed above. It first needs to be rinsed with water and then the titrant (0.1M NaOH). Hint you want to put the eyes above the buret, even though in real life achieving this height, to see above the buret, is not easy.

10. After filling the buret with the titrant you will start the titration curve. Add the pH probe and start the titration, continue until the pH stabilizes.

11. Answer the questions about the titration curve, sketch the titration curve in your notebook indicating the equivalence point, and select the indicator(s) you think would work best.

12. Next you will titrate! Follow the instructions to complete the section. Note that they want to readings to end in either .00 or .05.

13. The titration ends up using phenolphthalein, which turns pink at the endpoint. Ideally you want a faint/light pink color to get the most accurate results, this is easily done in the simulation but is harder to achieve in reality. You have added too much titrant when you see a dark pink color. Write down ALL start, end, and total volume numbers for NaOH, you’ll need them for your post lab.

14. After doing the three titrations, continue and complete the calculation questions, pay attention these questions will be helpful for your post lab.

15. When you arrive at the “Review” section, fill it out as you see necessary. Before exiting the simulation, click on the orange book at the bottom center of the screen. Click on the “Download PDF of Lab Book”. You will turn this into Canvas for proof that you did the simulation.


Report Sheet Name_______________

Virtual Aspirin Titration

RSC tration Code__________________







Start (NaOH) (mL)





End (NaOH) (mL)





Total NaOH (mL)





Moles of total NaOH





Moles of Aspirin





Grams of Aspirin in tablet






Molar Mass of Aspirin (C9H8O4) ___________________________


Show the math for at least one of your trials.

1) Calculate the moles of NaOH used in each trial

2) Calculate the moles of Aspirin for each sample.

3) Calculate the grams of Aspirin in the tablet for each trial.

4) Using your two closest (within 0.05mL of each other) calculate the average amount Aspirin in the tablet samples.

5) In the simulation, the average amount of Aspirin in their tablets ranges from 310mg to 315mg, did your average fall within in that range? If not, what could of caused that?

a. Using 313mg for the average number found in the simulation’s tablets, calculate the % yield (AKA % purity) of your average aspirin mass.

b. Bayer Aspirin claims their tablets contain 325mg of aspirin, calculate the % yield (% purity) of your average aspirin mass compared to Bayer’s.


(Report the two trials you ended up using for the average)


Total NaOH (mL)

Moles of Aspirin

Grams of Aspirin

% yield (compared to simulation mass)











Explain any sources of error that could have come from the “lab” work you did in the simulation. What are some errors that would have likely come from working physically in a lab instead of doing the simulation?



1) Explain why between phenolphethalein and bromothymol blue, phenolphthalein was the better option for the titration. Use the data from titraton curve in your explanation.

2) Why is it important to rinse glassware with water than the solution before using it with the solution?



1) When mixed HCl an acid and NaOH a base will react with each other.

a. Write the balanced neutralization equation for this reaction

b. What volume of 0.812M HCl is required to titrate 1.33g of NaOH to the endpoint?


2) The titration curve below is for a strong acid HCl (analyte) and a strong base NaOH (titrant).

 a) What’s the pH at the equivalence point? (doesn’t have to be extremely exact)

b) What will you find in your analyte between the volume (NaOH) of 0.1mL and 2.5mL? How about 3mL to 5mL?























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  1. Tutorial # 00797392 Posted By: dr.tony Posted on: 04/06/2021 04:16 AM
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