Transcript PPT-14-Making-soap - Papanui High School

Making soap
Soap is made by reacting a fat with sodium hydroxide.
Traditionally sheep fat (tallow) was used, but modern
toilet soaps are often made using vegetable oils such
as palm or olive oil (to make Palmolive).
To prove that any fat will do, in this demonstration we
use butter.
Put about 5 g of
butter in one test
tube, and an equal
volume of alcoholic
sodium hydroxide
solution in another
test tube.
Using alcohol as
well as water to
dissolve the NaOH
stops the butter
floating on top
instead of
reacting.
Heat the two tubes
together in a water
bath until the
butter is melted.
Then pour the
warm sodium
hydroxide solution
into the butter
and stir with a
stirring rod while
still heating.
The mixture will thicken
and become quite
viscous.
Use the stirring rod to
withdraw a little of the
jelly-like substance and
mix it with warm water
in a separate test tube.
Bubbles will form: we
have made soap.
This soap works best
in warm water.
When sodium hydroxide reacts with fat, the ester
links break to form the sodium salt of the fatty
acids contained in the fat (which is soap), and
glycerol (propan-1, 2, 3, triol).
We can separate out the soap from the glycerol by
adding saturated sodium chloride solution. The
solid soap rises to the top and can be skimmed off.
Soap.