Preparation of Soap





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Published on May 4, 2010

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Preparation of Soap.

1. Add about 150 mL water to a 400 mL beaker and heat the water with your burner to
about 85EC. You will need to mount a clamp above the beaker to hold the Erlenmeyer
flask (see below) upright in the water bath.
2. Add about 3 g (approx. a level, not heaping teaspoon) of shortening, coconut oil, or lard
to a small beaker and dissolve it in 25 mL of 95% ethanol. Do not use too much fat or
you will need more ethanol to dissolve it.
3. When the fat is completely dissolved, pour
the solution into a 125 mL Erlenmeyer flask
and add 15 mL of 30% NaOH solution. Swirl
the flask to mix the solution and add a few (3
to 5) boiling chips (Boilezer) to the flask.
4. Place the flask containing the fat solution in
the water bath and fasten it with a clamp to
hold it upright in the water bath. Place a
small watch glass over the mouth of the flask
to minimize evaporation of the alcohol. Place
an ice cube in the watch glass to more
effectively condense the alcohol.
5. Allow the the fat-alcoholic NaOH solution to boil for at least 30 min. [Note: do not boil
the water in the water bath]. If you observe undissolved fat in the flask, add a little
more ethanol to the flask and stir to dissolve the fat. Do not allow the hot water bath to
get too hot, keep it just hot enough to have controlled boiling of the fat solution.
6. While the saponification proceeds, prepare a salt solution by completely dissolving 20 g
NaCl in 100 mL deionized water in a 250 mL beaker. After the salt completely
dissolves, transfer about half of this salt solution to another beaker and place both
beakers of salt solution on ice to cool them.
7. After 30 min, test the fat solution to see if saponification is complete by placing a few
drops of the solution in a test tube of deionized water. If you see fat droplets float to the
top, the saponification is not complete and allow it to boil for an additional 10 min.
8. When saponification is complete, carefully pour the hot reaction mixture into one beaker
of salt solution and stir for a minute or two. Place the mixture on ice to cool it before
9. Set up a suction filtration apparatus with a Buchner funnel and filter paper (see Appendix
I for a diagram of the vacuum filtration apparatus). Filter the mixture from step 8, and
wash the soap (remaining in the Buchner funnel) twice with ice cold salt water (from the
second beaker). Draw air through the soap for a few minutes to remove most of the
10. Remove the soap cake from the Buchner funnel and save it for the following tests.

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