Name(s):
Period:
Date:
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 NaOH needed to titrate the aspirin
3. Calculate the volume of 0.10M NaOH required to titrate the aspirin
4. Complete titrations of each aspirin to find the experimental value
4. Compare the predicted amount NaOH 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 NaOH. 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 NaOH you will need in order to do the titration, then you will
proceed with the titration and find your error.
Materials
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1 baby aspirin
1 regular strength aspirin
1 extra strength aspirin
Mortar & Pestle
25mL or 50mL graduated cylinder
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Pipette
1 buret
Ring stand and buret clamp
0.10M NaOH
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Phenylthalein
125mL Erlenmeyer flask
DI water
Ethanol
Predictions
We are going to begin by calculating the volume of NaOH which we expect to use. The way we
predict the amount of reactants needed is through
stoichiometry.
First take a look at the reaction:
HC9H7O4 + NaOH  NaC9H7O4 + H2O
This is considered a neutralization reaction, because an acid (aspirin) and a base (NaOH) 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 NaOH 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
Name(s):
Period:
Calculate the molar mass of aspirin
Work:
Date:
Answer
Prediction: Baby Aspirin
Number of mg in one tablet
Number of grams in one tablet
Work
given
Answer
81mg
Work
given
Answer
325mg
Work
given
Answer
500.mg
Convert the grams into moles of aspirin
using the molar mass
Using your mole ratio, determine the
moles of NaOH required to neutralize this
sample of aspirin
If you have a 0.10M solution of NaOH
what is the volume of NaOH you will need
in L and mL? (M=moles/L)
Prediction: Regular Strength Aspirin
Number of mg in one tablet
Number of grams in one tablet
Convert the grams into moles of aspirin
using the molar mass
Using your mole ratio, determine the
moles of NaOH required to neutralize this
sample of aspirin
If you have a 0.10M solution of NaOH
what is the volume of NaOH you will need
in L and mL? (M=moles/L)
Prediction: Extra Strength Aspirin
Number of mg in one tablet
Number of grams in one tablet
Convert the grams into moles of aspirin
using the molar mass
Using your mole ratio, determine the
moles of NaOH required to neutralize this
sample of aspirin
If you have a 0.10M solution of NaOH
what is the volume of NaOH you will need
in L and mL? (M=moles/L)
Aspirin Titration HASPI Medical Chemistry Lab
Draft 2/28/2014
3
Name(s):
Period:
Date:
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
2
3
4
5
6
7
8
9
Response
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)
Add 10mL of ethanol to your mortar and mix with your powdered aspirin
Use a pipette to transfer the ethanol-aspirin solution to your erlenmeyer
flask
Add 25.0mL of DI water to the flask along with 2 drops of
phenolphthalein indicator. Swirl to mix.
Clean your buret. First rinse the buret with DI water, then rinse with
0.1M NaOH. Discard the water and NaOH used for rinsing. Fill your
buret with 0.100M NaOH, making sure to clear the tip of the buret.
Record the initial volume of NaOH in the data table.
Begin titrating. Add NaOH in 1mL increments while constantly swirling.
When the solution takes a longer time to turn clear, add NaOH 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.
Record the final volume of NaOH reached during your titration on your
data table
Clean out the Erlenmeyer flask and rinse with DI water.
Repeat steps 1-7 for regular strength and extra strength aspirin samples.
When all three titrations are complete, discard any remaining NaOH and
rinse your buret with DI water. Leave the buret clamped upside down
with the tip open to dry.
*Record data
*Record data
Data
Trial 1: Baby Aspirin
Initial Volume
NaOH
Final Volume
NaOH
Volume of
NaOH used
Trial 2: Regular Strength Aspirin
Initial Volume
NaOH
Final Volume
NaOH
Volume of
NaOH used
Aspirin Titration HASPI Medical Chemistry Lab
Draft 2/28/2014
Trial 3: Extra strength Aspirin
Initial Volume
NaOH
Final Volume
NaOH
Volume of
NaOH used
4
Name(s):
Period:
Date:
Data Analysis - Calculations
Results: Baby Aspirin
Number of mL required to reach endpoint
Number of moles NaOH titrated.
Remember it was 0.10M NaOH and
M=mol/L
Using your mole ratio, determine the
moles of aspirin neutralized by this
amount of NaOH
Calculate the grams of aspirin neutralized
in this trial of the experiment
Calculate the mg of aspirin neutralized in
this trial of the experiment.
Work
from experiment
Answer
Results: Regular Strength Aspirin
Number of mL required to reach endpoint
Number of moles NaOH titrated.
Remember it was 0.10M NaOH and
M=mol/L
Using your mole ratio, determine the
moles of aspirin neutralized by this
amount of NaOH
Calculate the grams of aspirin neutralized
in this trial of the experiment
Calculate the mg of aspirin neutralized in
this trial of the experiment.
Work
from experiment
Answer
Results: Extra Strength Aspirin
Number of mL required to reach endpoint
Number of moles NaOH titrated.
Remember it was 0.10M NaOH and
M=mol/L
Using your mole ratio, determine the
moles of aspirin neutralized by this
amount of NaOH
Calculate the grams of aspirin effectively
neutralized.
Calculate the mg of aspirin neutralized in
this trial of the experiment.
Work
from experiment
Answer
Aspirin Titration HASPI Medical Chemistry Lab
Draft 2/28/2014
5
Name(s):
Period:
Date:
Conclusions
1. Compare your predicted volumes of NaOH with your found volumes of NaOH using
the data table below.
%error = theoretical - actual x 100
theoretical
Baby Aspirin
Regular Strength
Aspirin
Extra Strength
Aspirin
Predicted
theoretical volume
of NaOH needed
Actual volume of
NaOH needed
Percent error
(show your work)
2. Acetyl salicylic acid (HC9H7O4) 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
5.
Aspirin Titration HASPI Medical Chemistry Lab
Draft 2/28/2014
6