Experiment #8: Saponification
Chemistry 102
Materials:
250 mL beaker, hotplate/stirplate, 600 mL beaker, magnetic stir bar, filter flask, Buchner
funnel, vacuum tubing, filter paper, pH paper, test tube, test tube stopper, olive oil,
ethanol, 25% KOH solution, ice
Procedures:
1. Don’t get the equipment for the filtration at first; just get what you need to get
started. If you have other stuff out it will just get in your way and possibly get spilled
on and/or get wet or dirty from the lab bench.
2. Prepare water bath immediately (before getting other equipment), as it will take time
to warm up: fill a 600 mL beaker about one-quarter full and begin heating it on a
hotplate. Don’t crank up the heat, as the soap will turn out better if the temperature
stays between 75° and 85° C
3. Zero the balance with the 250 mL beaker on the pan. Remove the beaker from the
balance, but don’t move away. Add olive oil to the beaker until you have 20.0 g.
4. Add 20 mL of ethanol to the 250 mL beaker. Measure out 14.5 mL of 25% KOH
solution and add it to the 250 mL beaker. Place the magnetic stir bar in the beaker.
5. Heat the 250 mL beaker in the hot water bath while stirring with the magnetic stir
plate. For proper stirring, place the beaker in the center of the plate so that the bar spins
around in the center of the beaker. Heat/stir for around 30 minutes, or until the
solution becomes clear with no separation of layers. Add 5 mL portions of
ethanol/water (1:1) to maintain volume. If excessive foaming occurs reduce the heat.
When done, remove the flask from the heat. Set the flask aside to cool and pour out the
hot water from the 600 mL beaker. After it cools a bit, you may use the 600 mL beaker
for an ice bath to chill the soap mixture. The bath should be prepared by putting in a
layer of ice and adding enough water to reach near the top of the ice layer while the ice
is still resting on the bottom. When the 250 mL beaker has cooled significantly, chill it
in the ice-water bath. If it has not cooled significantly, it is likely to break from the
heat stress on the glass. Before chilling (but after cooling), you may put in any
fragrance you wish to add.
6. “Salt out” the soap by adding 25 mL of saturated NaCl solution while stirring
vigorously with a glass rod. The subsequent increase in density of the aqueous phase
causes the soap to float.
7. Collect the soap by vacuum filtration ( I will set up an apparatus as a sample). Rinse
with a two small portions (approximately 5 mL each) of ice-cold water (chill some
distilled water in an ice bath). Pull air through for about 10 minutes to dry the soap.
Disconnect the hose from the aspirator before turning off the water. Otherwise soap
may be blown off the filtering apparatus.
8. Test your soap for pH. Place a bit of the soap in a test tube and add about 1 mL of
distilled water. Dip your stir rod (clean it first) into your soap solution and then touch
it to the pH paper. Determine the pH. If it’s too high (over 10), the soap is too caustic to
use on your skin.
9. Test your soap for sudsing ability. Stopper the test tube from part 8 and shake for
about 10 seconds. The soap should make suds.
10. Test your soap for ability to dissolve oil. Add a couple of drops of oil to your test
tube (from parts 8 and 9), stopper and shake for about 10 seconds. The oil should
dissolve into the solution.
11. Place your soap into a clean pre-weighed vial, and record the mass of soap
obtained.
Pre-Lab:
Prepare your notebook as described in the lab notebook handout. Include: name, title
of experiment, date, purpose, structure of triolein (main component of olive oil),
procedures (bulleted list) and a table for data and observations.
Report:
1. Summarize your results in a table (if you have not already done so).
2. Write a brief discussion of the experiment. In this section you should summarize
your results (mass of soap obtained and quality of soap), note any interesting
observations and make any possible conclusions about the experiment (successful vs.
unsuccessful and reasons why).
Be sure to compare your results to the
expected/desired results.
3. Answer the following post-lab questions:
a) Write the chemical reaction for the hydrolysis of triolein with aqueous KOH.
b) What is the purpose of rinsing the soap with cold water during the filtration
process?
c) Why do you think a mixture of ethanol and water is used (instead of just water) for
saponification?
4. Photocopy (or carbon copy) your notebook pages, attach summary, discussion and
questions (if not in notebook) and turn it in.