HASPI Medical Chemistry Lab Objectives 1. Calculate the number of moles of aspirin in each of the tablets 2. Calculate the number of moles of needed to titrate the aspirin 3. Calculate the volume of 0.10M required to titrate the aspirin 4. Complete titrations of each aspirin to find the experimental value 4. Compare the predicted amount with the amount used experimentally Scenario The active ingredient in aspirin is acetyl salicylic acid. Different strengths of aspirin are based on the amount of active ingredients that they contain. Titration is a way to determine how much acid is in a solution by adding just enough base, of a known concentration, to neutralize the acid. At the point of neutralization, the number of moles of acid (H+) is combined with an equal number of moles of base (OH-). You will perform a titration by dispensing a base of known volume and concentration into an acid solution of known volume but an unknown concentration. The aspirin will be titrated against a standard solution of base, 0.100 M. This base will be dispensed from a burette into a beaker containing the dissolved (in ethanol) acetyl salicylic acid and phenolphthalein indicator, which appears as a faint pink color in basic solutions In this lab you will be given three types of aspirin, baby aspirin containing 81mg of aspirin, regular strength aspirin containing 325mg of aspirin and extra strength aspirin containing 500.mg of aspirin. First you will calculate the amount of you will need in order to do the titration, then you will proceed with the titration and find your error. Materials 1 baby aspirin 1 regular strength aspirin 1 extra strength aspirin Mortar & Pestle 25mL or 50mL graduated cylinder Pipette 1 buret Ring stand and buret clamp 0.10M Phenylthalein 125mL Erlenmeyer flask DI water Ethanol Predictions We are going to begin by calculating the volume of which we expect to use. The way we predict the amount of reactants needed is through stoichiometry. First take a look at the reaction: HC 9 H 7 O 4 + NaC 9 H 7 O 4 + H 2 O This is considered a neutralization reaction, because an acid (aspirin) and a base () react to form a salt and water. If you look at the reaction you can see that this is balanced already with all coefficients of 1. Your goal is to calculate the number of moles of needed to neutralize each type of acid. Then you will determine how much of the 0.10M solution will be needed. *********, HASPI Medical Chemistry Lab ### 2
Calculate the molar mass of aspirin Work: Answer Prediction: Baby Aspirin Work Answer Number of mg in one tablet given 81mg moles of required to neutralize this If you have a 0.10M solution of what is the volume of you will need Prediction: Regular Strength Aspirin Work Answer Number of mg in one tablet given 325mg moles of required to neutralize this If you have a 0.10M solution of what is the volume of you will need Prediction: Extra Strength Aspirin Work Answer Number of mg in one tablet given 500.mg moles of required to neutralize this If you have a 0.10M solution of what is the volume of you will need Aspirin Titration HASPI Medical Chemistry Lab Draft 2/28/2014 3
Procedure/Directions Your lab team will be giving tasks, or directions, to perform on the left. Record your questions, observations, or required response to each task on the right. Task 1 Grind the children's aspirin into a fine powder using the mortar and pestle. (If you have already titrated the children's aspiring move on to the regular strength and extra-strength tablets) 2 Add 10mL of ethanol to your mortar and mix with your powdered aspirin 3 Use a pipette to transfer the ethanol-aspirin solution to your erlenmeyer flask 4 Add 25.0mL of DI water to the flask along with 2 drops of phenolphthalein indicator. Swirl to mix. 5 Clean your buret. First rinse the buret with DI water, then rinse with 0.1M. Discard the water and used for rinsing. Fill your buret with 0.100M, making sure to clear the tip of the buret. Record the initial volume of in the data table. 6 Begin titrating. Add in 1mL increments while constantly swirling. When the solution takes a longer time to turn clear, add drop by drop, and swirl well between drops. STOP titrating when the color change is permanent. The lighter the pink color the closer you are to the end point. 7 Record the final volume of reached during your titration on your data table 8 Clean out the Erlenmeyer flask and rinse with DI water. Repeat steps 1-7 for regular strength and extra strength aspirin samples. 9 When all three titrations are complete, discard any remaining and rinse your buret with DI water. Leave the buret clamped upside down with the tip open to dry. Response *Record data *Record data Data Trial 1: Baby Aspirin Trial 2: Regular Strength Aspirin Trial 3: Extra strength Aspirin used used used Aspirin Titration HASPI Medical Chemistry Lab Draft 2/28/2014 4
Data Analysis - Calculations Results: Baby Aspirin Work Answer Number of moles titrated. Remember it was 0.10M and amount of Calculate the grams of aspirin neutralized in this trial of the experiment Results: Regular Strength Aspirin Work Answer Number of moles titrated. Remember it was 0.10M and amount of Calculate the grams of aspirin neutralized in this trial of the experiment Results: Extra Strength Aspirin Work Answer Number of moles titrated. Remember it was 0.10M and amount of Calculate the grams of aspirin effectively neutralized. Aspirin Titration HASPI Medical Chemistry Lab Draft 2/28/2014 5
Conclusions 1. Compare your predicted volumes of with your found volumes of using the data table below. %error = theoretical - actual x 100 theoretical Baby Aspirin Regular Strength Aspirin Extra Strength Aspirin Predicted theoretical volume of needed Actual volume of needed Percent error (show your work) 2. Acetyl salicylic acid (HC 9 H 7 O 4 ) is a weak acid which means that hydrogen ions (H+) partially dissociate in solution. Nevertheless, the hydrogen ions that did dissociate were completely neutralized by the hydroxide ions (OH-). Describe how this can account for the percent error above. 3. Aspirin is an acid. As an acid it gives of hydrogens when put into solution. Study the reaction below and circle the hydrogen that is donated in this reaction. This is what we call the acidic hydrogen. 4. Using the following data table, calculate the cost effectiveness of each type of aspirin: Baby Aspirin Regular Strength Extra Strength Cost per bottle $11.98 $9.47 $9.29 Pills per bottle 300. 200. 100. Cost per pill Grams Effective *from your calculations Cost per pill = cost effectiveness grams effective Aspirin Titration HASPI Medical Chemistry Lab Draft 2/28/2014 6