CHEM-1112
General Chemistry Laboratory II
Spring 2009
Experiment 9B: From Oil of Wintergreen to Salicylic Acid
EXPERIMENTAL
A. Preparation of reaction
1) Add 60 mL of distilled water to a 250-mL beaker. Mark the level of the water
with a Sharpie or wax pencil
2) Pour out the water and dry the beaker
B. Reaction
1) Pour 4.0 mL methyl salicylate in a 10-mL graduated cylinder
2) Measure the total mass on an electronic balance and record in oyur notebook
3) Pour as much as possible of the methyl salicylate in the dry 250 mL beaker.
4) Measure the mass of the graduated cylinder. Calculate the amount of methyl
salicylate that you used
5) Add 40 mL of 6 M NaOH (sodium hydroxide) from a graduated cylinder in the
beaker
6) Stir the mixture with a glass stirring rod. Leave the rod in the beaker!
7) Place the beaker on a ringstand with metal gauze and boil gently for 15 minutes.
Stir the solution regularly
8) Make sure the volume remains 60 mL (the mark on the beaker). Add distilled
water
9) After boiling let the beaker cool for a few minutes, then put in ice
10) Add 50 mL DI water to the beaker
11) Then cautiously add 50 mL 8 M H2SO4 (sulfuric acid) to the beaker while stirring
12) Cool the beaker in ice
13) Cool 50 mL of DI water in an Erlenmeyer flask in an ice bath
Simon van Dijk, PhD
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C. Filtration and Recrystallization
1) Pour the cold mixture on a paper filter in a Buchner filter
2) Filter the mixture by suction filtration over a Buchner filter
3) Wash the crude extract with cold water
4) Continue the suction for several minutes to dry the precipitate
5) Wash and dry the 250-mL beaker during this time
D. Recrystallization
1) Transfer the precipitate on the filter to the beaker using a metal spatula
2) Add 100 mL of distilled water from a graduated cylinder
3) Heat the beaker with the solution on a ringstand with a metal gauze using a
Bunsen burner to a gentle boil
4) Stir with a glass stirring rod
5) Boil until all of the precipitate has dissolved
6) Remove the flame and let the solution cool for about 5 minutes
7) Crystals of salicylic acid appear after a few minutes. Record their appeance
8) Cool the beaker on ice until it is cold.
9) At the same time cool 50 mL DI water in an Erlenmeyer flask in ice
10) Filter the cold mixture by suction filtration
11) Wash the crystals with ice-cold water
12) Continue suction for about 15 minutes
13) Wash and dry the 250-mL beaker during this time
E. Drying the crystals
1) Determine the mass of the dry 250-mL beaker on an electronic balance
2) Transfer the crystal to the beaker
3) Write your name on the beaker and cover the beaker with a watch glass
4) Let it air dry until the next lab period
5) Determine the mass at the beginning of the next lab period
Simon van Dijk, PhD
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Experimental Notes
F. Recrystallization
1) When a desired product is formed by crystallization from a reaction mixture containing
excess reactants and other products, the crystals are likely to be relatively impure. The
crystals can be separated from the impure solution (often called “mother liquor”) by
filtration or decantation. The mother liquor clinging to the crystals can be removed by
washing with an appropriate solvent. However, washing will not remove impurities
occluded in the crystals.
2) A standard method for purifying a crystalline product is recrystallization. For crystals
that are more soluble in hot solvent than in cold solvent, the recrystallization can be done
by dissolving the crystals in a minimum quantity of hot solvent and then cooling. The
purified crystals can then be “harvested” by filtration. Larger, purer crystals are obtained
if the hot solution is allowed to cool slowly without being moved or disturbed. A second
“crop” of crystals could be obtained from the filtrate by evaporating a fraction of the
solvent by heating followed by cooling the remaining solution. The second crop of
recrystallized product is generally less pure than the first.
3) The wet crystals dry very slowly. The purpose of the acetone is to wash the water off the
crystals. The acetone, which has a high vapor pressure, evaporates quickly leaving the
crystals dry.
4) The product will slowly decompose when exposed to light. Hence the crystals should be
stored in the dark.
G. Filtering by suction
1) Filter the crystals by vacuum or suction filtration using a Buchner funnel and clean filter
flask. Be sure to clamp the filter flasks when they are connected to the hose. If your crop
of crystals appears to be quite small, save the filtrate so that you can obtain a second crop
of crystals. Consult your instructor about the procedure.
2) Wash the crystals twice with ice water. Use less than 5 mL of ice water for each wash
and work quickly to avoid dissolving the product in the wash water. After the final wash
let the crystals air dry.
3) When the crystals are dry, determine their mass by weighing on a balance to the nearest
0.001 g (make sure you use weighing paper and are careful to avoid loss of crystals).
Simon van Dijk, PhD
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Chemicals
Methyl salicylate
Formula:
Mole mass
Melting point
Boiling point
Density
Solubility
Appearance
C8H8O3
152.1494
19.4 oC
220 – 224 oC
1.174 g/cm3
<0.1 g/100 mL at 19 C
Colorless, yellowish or reddish oily liquid
Sulfuric acid
Formula:
Mole mass
Melting point
Boiling point
Density
Solubility
Appearance
Comments
H2O4S
98.0734
3 oC
280 oC
1.84 g/cm3
Soluble. Miscible/Reactive
Colorless (pure) to dark brown, oily, dense liquid with sharp, acrid odor.
Corrosive material
Sodium hydroxide
Formula:
Mole mass
Melting point
Boiling point
Density
Solubility
Appearance
Comments
NaOH
39.99707
318 oC
1390 oC
2.13 g/cm3
50 g/100 mL. Highly soluble
Colorless, odorless solid.
Corrosive material
Salicylic acid
Formula:
Mole mass
Melting point
Boiling point
Density
Solubility
Appearance
Comments
C7H6O3
138.1226
159 oC
211 oC at 20 mm Hg
1.44 g/cm3
<0.1 g/100 mL at 19 C
Colorless, yellowish or reddish oily liquid
Moisture sensitive; light sensitive
Simon van Dijk, PhD
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