R
Name:
Lab 3: Synthesizing and Testing the Purity of Aspirin
Question:
Are brand name commercial prescription drugs better than generic or homemade prescription drugs?
Background:
In October 2012, an outbreak of fungal meningitis was reported in the United States. Federal health officials
expanded the recall list of potentially contaminated injectable medications suspected in a multi-state meningitis
outbreak and the death of five people; 47 people contracted meningitis in seven states. The Food and Drug
Administration released a list of 34 different potentially contaminated drugs that included steroids, epidural anesthetics
used to block pain during childbirth, and surgery and saline solutions that are compounded to make different
medications. All of the products on the recall list were made by the New England Compound Center (NECC) in
Massachusetts, and are administered by injection into the spine.
The recalled drugs were contaminated by a fungus, linking to the meningitis outbreak observed among patients
who received injections of a steroid that is injected into the spinal cord. Patients showed symptoms like worsening
headaches, fever, stiff necks, trouble walking, and progressing back pain, all symptoms representative of meningitis. FDA
inspectors found the fungus in a sealed vial of the steroid at the NECC when numerous cases of meningitis in multiple
states sparked health alerts and recalls. The NECC voluntarily shut down operations in response.
Seven states have reported meningitis cases related to the contaminated steroid, including Tennessee,
Maryland, Virginia, North Carolina, Florida, and Indiana, and Michigan. In Tennessee, the state hardest hit with the
meningitis outbreak, 29 people have been diagnosed with meningitis, and three people have died. State health officials
are working with clinics to contact other patients who might have been exposed to the fungus. Tennessee Health
Commissioner Dr. John Dreyzehner said “Evidence indicates these clinics and clinicians had no way of knowing about the
contamination at the time of the procedure. The evidence indicates this is a product issue.” Members the U.S. House of
Representatives and the U. S. Senate requested federal health officials provide them with briefings on the outbreak as a
first step toward possible legislative action to strengthen federal drug safety regulations, thus focusing on drug purity in
order to ensure patient safety including everything from over the counter drugs to prescription drugs. Drug purity is the
measurement of extra matter in a drug that may or may not be harmful to the recipient of the drug.
Aspirin is the most widely used over-the-counter drug in the world. Aspirin originally was derived by boiling the
bark of the white willow tree, and it is used to relieve pain, reduce inflammation, and lower fever. Felix Hoffman and
Arthur Eichengrün first synthesized the active ingredient in aspirin, acetylsalicylic acid, in 1893.The average tablet
contains about 325 milligrams of acetylsalicylic acid.
You can determine the quality of aspirin by adding iron III chloride – Fe(III)Cl – to different aspirin samples, and
observe the color change that may occur. Pure aspirin would show no color, whereas impure aspirin would show a
purple color. Such impurities come from excess salicylic acid found in the aspirin.
Similar to the importance of drug purity is measured drug dosage. A drug dose is the specific amount of
medication to be taken at a given time. In your life, you have probably been warned about the dangers of dozens of
different substances, from pesticides to poisonous wild mushrooms. You know better than to drink your shampoo or rub
gasoline on your skin. But how is toxicity determined in the first place? And how is it that some things that are good for
you, like vitamin tablets, can be toxic or even lethal in higher doses?
One way to measure toxicity, other than assessing something’s purity, is to measure the lethal dose (LD50) of a
substance, the amount of substance that can cause death. The LD50 of a substance is the amount of substance that
causes the death of half of the animals exposed to it.
The following table provides the LD50’s for several common substances in grams, milligrams, or micrograms (mcg; onemillionth of a gram) of substance per kilogram of body mass.
Table 1. Lethal Doses
Lethal Dose
Common
Chemical Name
(LD50) per kg
Name
and Formula
body mass
Toxic Response
Acetylsalicylic
Confusion, upset stomach, psychosis, ringing ears,
Aspirin
acid, C9H8O4
200mg/kg
drowsiness, hyperventilation
Sodium chloride,
Table Salt
NaCl
12,357 mg/kg Eye irritation, elevated blood pressure
Vomiting, diarrhea, internal bleeding, kidney & liver
Castor Beans
Ricin
30 mg/kg
failure
Arsenic (III) oxide,
Irritates eyes & skin, nausea, internal bleeding,
Arsenic
As2O3
15 mg/kg
kidney damage
Depressed activity, stomach pains, heart disease,
Sugar
Glucose, C6H12O6
30mg/kg
blindness, kidney damage
Paralysis, suffocation, loss of consciousness,
Snake Venom
C338H529N97O105S11
25 mcg/kg
seizures, internal bleeding
Caffeine,
Coffee Beans
C8H10N4O2
167 mg/kg
Nausea, psychosis, increased pulse, convulsions
*A small LD indicates that it does not take very much of the substance to produce ill effects. Substances with small LD50’s
should be avoided.
You may be surprised to see lethal doses for substances like sugar and aspirin. These substances are usually considered
beneficial. However, everything is toxic in a large enough does, even life-sustaining substances like water and oxygen.
To take size into account, the LD50 is reported in milligrams per substance per kilogram of body weight.
LD50 = mg substance/kg body weight
Thus, the LD50 can be determined specifically for any human of any size.
Introduction:
Your introduction for this lab should include the following items:
- Purpose (WHAT are you trying to determine in this lab and HOW are you going to determine that)
- Background information (to support your WHAT and HOW aspects of your purpose)
- Explanation of why drug purity and drug dosage are important (how can each affect our lives?)
Hypothesis:
Form a hypothesis about the purities of homemade aspirin to different generic, manufactured aspirins. How
might they vary? Be sure to explain your reasoning.
Pre – Lab:
1. Based on the background reading, which of the following statements is true?
a. A high LD50 value means the more toxic a substance is
b. Neither a high or low LD50 values identify how toxic a substance is
c. A low LD50 value means the more toxic a substance is
d. A low LD50 value means the less toxic a substance is
C7H6O3(s) + C4H6O3(aq)  C9H8O4(s) + C2H4O2(aq)
(salicylic acid) (acetic anhydride) (aspirin)
(acetic acid)
2. Is the above reaction balanced? (Record the above reaction in your final lab report)
3. Is the above reaction a chemical or physical reaction? How do you know?
4. Determine the Molar Mass of each reactant and product shown in the reaction equation above. SHOW ALL
WORK.
5. What is the mass of 0.02 moles of C7H6O3?
Materials:
 Salicylic acid
 6 mL acetic anhydride*
 5-8 drops of sulfuric acid*
 50 mL water
*Use extreme caution when handling these chemicals.
Sulfuric acid and acetic anhydride can cause severe
burns.
Equipment:
 filter paper
 one glass beaker
 one 400 mL beakers
 two 125 mL Erlenmeyer flask
 100 mL graduated cylinders
 fume hood, hot plate, electronic balance
 pipette
 stirring rod with rubber-policeman
 ice bath
 wash bottle
 four test tubes with blue rack
Procedures: Record any observations, or errors made while performing the following lab. In this laboratory exercise, you
can prepare aspirin (acetylsalicylic acid) from salicylic acid and acetic anhydride using the following reaction:
Day 1 Procedures
1. Using a weigh boat, weigh out the mass of salicylic acid you determined in your pre-lab. Record how much salicylic
acid you actually measured. Don’t forget your units!
2. Transfer the solid to a dry 125mL Erlenmeyer flask.
3. Using a 100mL graduated cylinder, measure 6 mL of acetic anhydride in the hood.
4. Add the 6 mL of acetic anhydride to your 125 mL Erlenmeyer flask.
5. Using the provided glass beaker at your lab bench, fill the beaker up with about 100 mL of water, and place the
beaker on the hot plate.
6. Set the hot plate setting to a 3 to warm up the water. DO NOT boil the water, simply get it warm.
7. In the hood, use the provided dropper to add 5-8 drops of sulfuric acid to the flask.
8. Back at your lab bench, gently swirl the flask to mix the solution. Place the flask in the glass beaker of warm water
for about 15 minutes. DO NOT stray from your solution! Watch it to ensure that nothing goes wrong.
9. Using a pipette, add 20 drops of cold water dropwise (drop-by-drop) to the warm solution to destroy the excess
acetic anhydride.
10. Use your 100mL graduated cylinder to measure out 20mL of water. Add those 20 mL of water to the flask. Set the
flask in an ice bath to cool the mixture and speed crystallization (the formation of crystals).
11. When the crystallization process appears complete, pour the mixture through the filter funnel.
12. After most of the water filters from the solid, wash the crystals with a few milliliters of ice cold water. Be sure the
water is near freezing to minimize loss of product.
13. Using a pencil to write your group names on a new, clean, dry filter paper. Weigh the filter paper and record its
mass.
14. Using the rubber-policeman, scrape the solid onto a dry filter paper.
15. Carefully walk your sample of aspirin to the heat lamp corner to help dry the aspirin.
Day 1 Data:
Mass of salicylic acid =
Mass of filter paper =
Day 2 Procedures
1. Collect your aspirin sample from the heat lamp corner. Weigh your sample and filter paper. Record the mass of
your aspirin and filter paper as well as any observations about your aspirin sample (color, shape, texture).
2. Label 4 test tubes numbers 1 – 4.
3. Using the rubber-policeman scrape some of your aspirin sample into test tube #1.
4. Collect small amounts of 3 brand name aspirins in the 3 remaining test tubes. Be sure to label which brand of
aspirin is in which number test tube.
5. Set all 4 test tubes in the blue test tube rack.
6. Using a pipette, add one drop of iron III chloride to each of the separate test tubes containing a few crystals of
each substance. Observe and record the color. Be very specific when describing the shade and intensity of the
color. (Pure aspirin would show no color, while salicylic acid or traces of it in impure aspirin will show a purple
color.)
Day 2 Data:
Mass of filter paper with aspirin =
Mass of aspirin =
Aspirin Brand
Color Observation
Assessment of Purity
Post-Lab Calculations: Don’t forget to label your units!
Percent yield = the amount of product obtained in a chemical reaction
Percent error = how accurate your measurements were
1. Theoretical Yield –
Using the mass of salicylic acid (C7H6O3) you used to synthesize aspirin, how many grams of aspirin (C9H8O4) did
you theoretically produced? Hint: use the mole hill!
2. Determine your percent yield using the following mathematical formula:
Percent yield = (actual yield ÷ theoretical yield) x 100%
Actual yield = mass of aspirin created
Theoretical yield = answer from question 2
3. Determine your percent error using the following mathematical formula:
Percent error = | actual yield – theoretical yield | x 100 %
theoretical yield
4. How much aspirin is considered the lethal dose for you? Use the following steps to determine the amount of
aspirin that would be considered the LD50 for you.
1. Convert your body weight from pounds to kilograms (kg) by multiplying your body weight by 1kg/2.2lbs.
2. Multiply your weight (in kg) by the lethal dosage for aspirin found in table 1.
3. Convert the number of milligrams determined in step 2 to grams by multiplying milligrams by
1g/1000mg.
5. LD50 Applications:
a) If a person weighs 166 pounds (lbs), how much aspirin is considered the LD50 for that individual? Hint: Use
the steps listed above.
b) Ethanol is a grain alcohol; the LD50 for ethanol is 7060 mg/kg. How many grams of ethanol would be lethal to
a 135 lb adult?
6. HONORS: You can compare the actual and theoretical yield of aspirin based on the initial quantity of salicylic
acid. If 6mL of acetic anhydride (C4H6O3) weighs 6.49g, which reactant was the limiting reagent in the synthesis,
salicylic acid (C7H6O3) or acetic anhydride?
Conclusion:
When writing your conclusion, consider RERUN. Be sure to answer the purpose to the lab, and discuss whether you
reject or accept your hypothesis. As always, use your data and observations to support your conclusion. Reference your
responses to both Pre-lab and Post-lab questions to strengthen your conclusion.