Synthesis of Aspirin
CLAB 104 – Lab 9
Experiment IX: Synthesis of Aspirin
In today’s laboratory we will carry out the following
synthesis reaction:
Sulfuric
Acetic
Aspirin
Salicylic
Acetic
Acid

Acid
+ Anhydride Catalyst
+ Acid
(C2H4O2)
(C9H8O4)
(C7H6O3)
(C4H6O3)
+

+
This is a stoichiometrically-balanced equations:1 mole of each
reactant will produce 1 mole of each product.
Laboratory Procedure
1. In a weigh boat, accurately weigh out and record the mass
of around 5 g of salicylic acid. Add this plus 10.0 mL of
acetic anhydride, and 25 drops of concentrated sulfuric acid
into the same beaker. (Suppose for sample calculations that you
added 2.113 g of salicylic acid and 6.00 mL of acetic anhydride)
Sulfuric
Acid
Salicylic
Acid
Acetic
Anhydride
EVERYTHING NECESSARY TO CALCULATE THE THEORETICAL
YIELD OF ASPIRIN HAS NOW BEEN MEASURED.
Finding the Theoretical Yield of Aspirin
a. The molar mass of salicylic acid is 138.1 g/mole. Use this
to find the moles of salicylic acid used:
1mole
From sample
2.113 g 
 0.01530 mole
data:
138.1 g
b. Using the density of acetic anhydride of 1.081 g/mL,
calculate the mass of acetic acid added.
1.081 g
From sample
6.00 mL 
 6.49 g
data:
mL
c. The molar mass of acetic anhydride is 102.1 g/mole. Use
this to find the moles of acetic anhydride used:
From sample
data:
1mole
6.49 g 
 0.0636 mole
102.1 g
Laboratory Procedure
d. From the 1:1 stoichiometry of reactants, determine which
is the limiting reagent:
0.01530 moles salicylic
acid added
Limiting Reagent
0.0636 moles acetic
anhydride added
e. From the 1:1 stoichiometry of products to reactants,
calculate the number of moles of product theoretically formed:
1mole aspirin
0.01530 mole salicylic acid 
1 mole salicylic acid
 0.01530 mole aspirin
Laboratory Procedure
f. The molar mass of aspirin is 180.1 g/mole. Use this to find
the theoretical yield of aspirin in grams:
180.1 g
0.01530 mole 
 2.756 g
mole
Follow the procedure on page 97 to complete your
synthesis of aspirin.
50 mL
ice water
2. Swirl beaker to break up any
large chunks. Allow reaction
to proceed for 20 minutes. After
that time, add 50 mL of ice
water. Place the beaker into a container with ice in it to further
cool your sample. Aspirin should crystallize in the beaker.
Laboratory Procedure
Rinse crystals
and beaker
several times
Place filter
paper in
funnel
Attach hose
to faucet
3. Filter the crystals using a
Buchner funnel. Wash the filter

paper several times with distilled water.
side-arm
After filtration is complete, carefully
remove your filter paper from the funnel.
Place it in a weigh boat with your names on it so that it can
dry and be weighed during next week’s lab period.
4. Place a small chunk of your wet aspirin in a test tube. Add
about 10 mL of water to the test tube and dissolve the chunk.
Laboratory Procedure
5. Add 3 drops of yellow FeCl3 solution. Record your
observations. (A change of color to purple is a qualitative test
that shows the presence of salicylic acid. If your test tube
turns purple, has all your reactant been consumed?)
6. The following week, weigh and report the mass of your
dried sample of aspirin Calculate the %yield of aspirin in
your experiment: (Suppose your experimental yield is 1.884 g
from our practice problem where we determined a theoretical yield
of 2.756 g of aspirin)
experiment al yield
1.884 g
% yield 
100 
100  68.36%
theoretical yield
2.756 g