Investigation: Making a Soap
Name:
Soap has been made for thousands of years, although the regular use of it in
the western world is far more recent. For some interesting history, search the
internet for information on the “soap tax” – fascinating story!
Preparation:
1. Read carefully through the instructions below. On the back of this
sheet, convert the written steps into a flow chart you can follow next
lesson when you make the soap.
2. Stop and review the safety for this experiment. Write a list of the
safety precautions you think are necessary. Your teacher will review
these before starting.
3. What does “decant” mean? Describe in words how to do it.
Aim:
To hydrolyse a vegetable fat to make soap.
2 x 250ml beakers, 1 x larger plastic container Bunsen etc, glass stirring rod,
vegetable fat (solid e.g. copha), NaOH (6M), saturated NaCl solution, 10ml measuring cylinder,
metal teaspoon.
Materials & Apparatus:
Warning: the NaOH is very caustic – it burns skin. Handle with care and observe safety
instructions given by your teacher.
Method:
1.
2.
3.
4.
Review safety precautions.
Add a teaspoonful of dripping to the beaker. Heat gently until it melts.
Add 10ml of NaOH, while stirring (wash out the cylinder thoroughly).
Boil gently for about 15 minutes, constantly stirring. Check the mixture, if it is starting to
turn into a solid, reduce the heat and keep stirring. When it turns to a gluggy solid, stop
heating.
5. Add 10ml of NaCl solution. Stir to dissolve. Boil gently for 5 minutes.
6. Allow to cool, stirring.
7. Wash the soap several times, decanting the excess liquid. Filtering will not work – takes
ages.
8. Shape into a bar of soap.
9. Wash the soap by running under water – to remove excess base.
10. When set, test to see if it lathers.