Aspirin Titration Lab

ACADEMIC CHEMISTRY NAME: PERIOD DATE: ASPIRIN TITRATION LAB

PRELAB Read the entire lab and answer the following questions. You may need to consult the internet to answer some of the following questions.

1. What is the name of the acid included in aspirin? 2. What is the formula of aspirin? 3. What is aspirin’s theoretical molar mass? 4. Draw a structural formula for acetylsalicylic acid and label the carboxyl group and the acidic hydrogen.

PURPOSE 1. conduct an acid base titration to determine the molar mass of aspirin 2. measure the volume of a known concentration of basic solution using proper titration techniques and equipment (buret) 3. calculate the number of moles of base needed to reach the endpoint and compare to the number of moles of acid

BACKGROUND Aspirin is slightly acidic and reacts with bases in neutralization reactions. If the reaction is followed with an indicator, a color change will occur when the acid is completely neutralized and one drop of excess base has been added. The number of moles of base consumed and the number of moles of acid in the sample can be calculated form the volume of the base needed to obtain the color change. The relationship between these two mole values is determined form the balanced chemical equation for the reaction. In this experiment, you will titrate an aspirin tablet with a known concentration of sodium hydroxide solution. The end point will be determined with phenolphthalein or thymol blue indicator. The following simplified equation describes the neutralization reaction that will be observed in this experiment.

H-Asp (aq) + NaOH (aq)  Na-Asp (aq) + H2O (l)

Because the mole ratio is 1:1, the number of moles of the base will equal the number of moles of acid at the equivalence point of the titration. The molar mass of the solid aspirin can be approximated by dividing the mass of the aspirin in the tablet by the moles of aspirin present. The mass of the aspirin inside the tablet is usually near 325 mg. Inactive ingredients, such as binders, are added to the aspirin during the manufacturing process. Therefore, the actual mass of the tablet exceeds 325 mg because it is not 100% pure aspirin.

MATERIALS 100 ml of distilled water in a wash bottle 50 ml of 0.100 M NaOH 40 mL of 95% ethanol phenolphthalein or thymol blue indicator (3 drops per titration) 325 mg non buffered aspirin tablets 1000 ml graduated cylinder 250 ml Erlenmeyer flasks, 2 ACADEMIC CHEMISTRY NAME: PERIOD DATE: buret buret clamp and ring stand funnel

PROCEDURE Please wear goggles throughout the lab. Thoroughly wash away any solutions that you may get on your skin.

PARTNER A 1. Assemble the ring stand, buret clamp, and buret. 2. Clean the buret according to the procedure outline in class. 3. Rinse the buret with 3 mL of 0.100 M NaOH solution. 4. Fill the buret with 0.100 M NaOH to just above the 0.00 mark. Allow some of the solution to drain through the tip and record the initial volume of NaOH to 2 decimal places.

PARTNER B 1. Weigh an empty Erlenmeyer flask. Add an aspirin table to the flask and weigh again. Add about 20 ml of distilled H2O. Wait 20-30 seconds. The tablet will break apart as it absorbs water and swells. Then add about 20 ml of ethyl alcohol to help dissolve the aspirin. 2. Add 3-4 drops of phenolphthalein indicator and swirl the flask.

TOGETHER 1. Titrate to the endpoint with 0.100 M NaOH. Record in the data table the volume of base that was required. 2. Repeat the procedure with a second aspirin tablet. IF time permits, you may perform a 3 rd titration. 3. Wash all equipment when finished. Be sure to rinse the buret with distilled water and leave it to dry by inverting it in the buret clamp. ACADEMIC CHEMISTRY NAME: PERIOD DATE: DATA TRIAL Mass of NaOH NaOH final Volume of Volume Concentration of NaOH asprin initial volume NaOH of NaOH tablet volume reading delivered delivered reading (L) U nits: 1

TRIAL Moles of Moles of (experimental (theoretical) % error NaOH at aspirin at ) Molar mass Molar mass endpoint endpoint of aspirin of aspirin Units:

CALCULATIONS

1. Volume of NaOH delivered

2. Volume of NaOH delivered (L)

3. Moles of NaOH at endpoint ACADEMIC CHEMISTRY NAME: PERIOD DATE:

4. Moles of aspirin at endpoint

5. Experimental molar mass of aspirin

6. % aspirin in the tablet

7. Average molar mass of aspirin

8. Average deviation of the three trials (experimental molar masses)

9. Average % error

POST LAB 1. If there was another additive to the aspirin tablet, say vitamin C, how would this affect the results for the titration of the aspirin? 2. If titrated properly, the neutralized aspirin solution color will fade over time. Why might this be? (hint: relates to CO2 in the air). 3. An impure sample of ascorbic acid, with a mass of 2.06 grams is dissolved in water. It is titrated with 0.200 M sodium hydroxide. The sample required 46.0 ml to reach an endpoint using phenolphthalein as the indicator. a. Calculate the number of moles of ascorbic acid in the sample. b. Calculate the mass of ascorbic acid in the sample (hint: you need the molar mass of ascorbic acid) c. Calculate the % purity or the sample (mass of ascorbic acid/ mass of sample X 100) 4. Calculate the concentration of acetic acid, if an average of 67.0 ml of .468 M magnesium hydroxide is required to titrate 50.0 ml of the acid in order to reach the endpoint. a. Write the balanced neutralization reaction that occurs. ACADEMIC CHEMISTRY NAME: PERIOD DATE: b. Calculate the concentration of acetic acid. 5. Calculate the concentration of KOH if 65.0 ml of the base are used to titrate a 15.0ml sample of 1.0M H2SO4. a. Write a balanced neutralization reaction.