Intro to Chemistry Chem1020 Lab
Preparation of Aspirin
Chemistry Department
Minneapolis Community & Technical College
1
Overview
• Part I
Introduction
• Part II
Synthesis of aspirin
• Part III
Separation of aspirin
• Part IV
Testing of aspirin
• Part V
Calculation
2
Part I. Introduction
• In this experiment you will learn how to use a chemical reaction to
make new substances such as aspirin:
Salicylic acid + Acetic anhydride
Aspirin + Acetic acid
• You will also learn how to separate the desired product from other
substances, which is as important as the synthesis itself.
• During the following week, you will evaluate the quantity and
purity of the aspirin product.
• Stoichiometric calculation, a topic
covered in Chapter 8.4 in the textbook, will be performed on this reaction.
3
Part II. Preparation
~ 1.5 g salicylic acid
~ 2 mL acetic anhydride
• Use the provided graduated
• Use the attached spatula for
cylinder to measure.
transferring.
• Weigh it on a diagonally-folded
and zeroed weighing paper.
• Record its exact mass.
An
Erlenmeyer
flask
4 drops phosphoric acid
• It serves as a catalyst, which
speeds up reaction without
changing its own
composition.
• Use the provided pipette
dropper.
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Part II. Precautions!
• For any chemicals, always put the cap back onto its container after
each use, even if someone will be using it right after you.
• Salicylic acid is a fluffy solid. Be careful not to make a mess at the
weighing station. In case of spilling, alert the instructor immediately.
• Both acetic anhydride and phosphoric acid are corrosive and reactive.
o Keep them inside the fume hood.
o Be careful not to get it onto your skin.
o In case of spilling, alert the instructor immediately.
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Part II. Preparation
(Heating is done in fume hood)
1. Clamp and tilt the
Erlenmeyer flask allowing
the solid to mix with the
liquid inside the flask.
2. Lower the flask into a waterbath which sits above a hot
plate. Insert a thermometer
into the water-bath (not the
flask) to monitor temperature.
Turn on the heating knob (the
right one) of the hot plate all the way to “high”.
Setup side view
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Part II. Preparation
3. When the temperature reaches 80 ºC, turn off the hot plate.
.
4. Swirl the flask gently to let all solids dissolve. If you have to
take the flask out of the water bath to shake, put it back as soon
as all solids dissolve. Keep it in the water bath for 5 minutes.
5. Take the flask out of the water bath and let it cool down
undisturbed (meaning no shaking or stirring). Eventually most
of the liquid will crystallize, generating a white, crystalline cake
at the bottom of the flask. That solid, should be mainly the
aspirin product.
6. Add enough ice-cold water into the flask and use a glass stirring
rod to break up the solid chunks.
Ice-cold distilled water
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Part III. Separation
Now the solid aspirin is mixed with other substances: unreacted reactants,
phosphoric acid catalyst, acetic acid – the other product. To separate
aspirin from them, vacuum filtration will be used.
Buchner funnel
Setup side view
Setup front view
filtration flask
electric pump
on/off switch
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Part III. Separation
1. Determine and record the total mass of
a watch glass and a filter paper. Write
your name on the edge of the paper.
3. Turn on the pump. Quickly swirl and
pour the reaction mixture into the
funnel. Use the ice-cold water to
rinse out all solid in the flask.
4. Squirt more ice-cold water onto the
crystals in the Buchner funnel to wash
away other impurities.
John D.
2. Put the filter paper into the Buchner funnel.
Wet it with ice-cold water so that it fits
nicely in the funnel.
5. Use a micro spatula to pick out the
filter paper with aspirin, and put them
on the watch glass for drying over
one week.
John D.
Ice-cold distilled water
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Part IV. Testing
• Quantity
(Done a Week Later)
Determine and record the total mass of watch glass, filter
paper, and aspirin product
• Quality
Determine the purity of your product:

Your instructor will demonstrate that pure salicylic
acid (one of the reactants) and pure commercial
aspirin show different colors when mixed with an
FeCl3 solution.

Use the provided semi-micro spatula to transfer a
small amount (match-head size) of your product into
the test tube, and add 2 drops of 1% FeCl3 solution.
Compare the resulting color to the instructor’s results.
Draw a conclusion about the purity of your product.
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Part V. Sample Calculation
Data:
a. Msalicylic acid
1.52 g
c. Mwatch glass + filter paper + aspirin
b. Mwatch glass + filter paper 19.18 g
20.98 g
Calculation:
a. Actual yield of aspirin = Mwatch glass + filter paper + aspirin - Mwatch glass + filter paper
= 20.98 – 19.18 = 1.80 g (2 decimal places)
b. Theoretical yield of aspirin
Salicylic acid + Acetic anhydride
Molecular formulas: C7H6O3
Molar masses:
1.52g S.A. 
138.12 g/mol
Aspirin + Acetic acid
C9H8O4
180.16 g/mol
1mol S.A. 1mol Aspirin 180.16g Aspirin


 1.98g Aspirin (3 sig. fig.)
138.12g S.A. 1mol S.A.
1mol Aspirin
c. Percent yield 
Actual yield
1.80g

 100%  90.9% (3 sig. fig.)
Theoretica l yield 1.98g
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