Elementary
Lesson for Making Soap
Developers:
David
Crotty
Franklin Elementary
Pennsauken, NJ
Mike
Gavaghan
Separations Technology
Rohm & Haas Company
Spring House, PA
Faith
Lipford
Separations Technology
Rohm & Haas Company
Spring House, PA
Grade
Level:
5
through 8
Discipline:
General
Science, Chemistry
Goals:
Upon
completion of this lesson, the student will:
1.
recognize and use chemical indicators in the lab.
2.
recognize the need for safety while doing chemical experiments.
3.
understand the need for following precise directions.
Objectives:
Upon
completion of this lesson, the student will be able
to:
1.
use pH paper to determine if soap is acidic or alkaline.
2.
define saponification and emulsion
3.
manufacture a soap sample.
4.
compare the relative strength of their sample against
commercial soap products
Background:
Evidence
of soap making dates back to the Egyptians and Babylonians.
However, due to the harshness of homemade soaps and
the expense of early commercial products, humans have
been using soaps to clean clothes and themselves for
a relatively short period of time.
Homemade
soaps were usually made from kitchen fats or lard. The
fats were
broken down using ash soaked in water. The soaking ash
produced the needed hydroxide.
The samples the students will manufacture will be made
from the same process.
Saponification
is a process in which a fat molecule is broken down
by sodium hydroxide (lye) into four smaller molecules;
three of the new molecules are soap and one is glycerol.
The glycerol molecule keeps the soap moist. Emulsion
is a temporary mixing of two insoluble liquids such
as oil and water.
Activity
1: Making Soap
Teacher
Preparation:
SAFETY
NOTE: Both ethyl and isopropyl alcohol are
flammable. Sodium hydroxide is caustic. Use care with
these chemicals. Students should be familiar with lab
safety procedures before beginning this experiment (see
page 4). Make sure there is no open flame in the
room. Use goggles, gloves, aprons, or lab coats.
For
the class: (the following will provide
enough solutions for 50 experiments)
1.
Prepare sodium hydroxide and alcohol solution. Place
120g of sodium hydroxide (sodium hydroxide is available
at hardware stores under the name Lye. Avoid using liquid
drain cleaners) in a glass container. Add enough
water to make 500 ml of solution. Stir to dissolve.
Add 500 ml of either ethyl or 70% isopropyl alcohol
(available at drug stores). (Wear safety glasses
when you prepare this solution. It can cause serious
damage to the eye.)
2.
Prepare fat: Solids such as Crisco work best. Melt
approximately 1 kg of Crisco or another vegetable shortening
into a container suitable for heating. Heat fat to 40
to 45 degrees C. The fat must stay in liquid form until
distributed to the students.
For
each group:
Container
with at least 100g of either table salt or kosher salt.
Balance scale.
Heating tray or electric burner.
20ml of sodium hydroxide/alcohol solution
20ml of melted fat or oil.
Soup can
Glass custard cup or container to fit into the mouth
of the soup can (see diagram 1).
Safety goggles and aprons.
Wooden stirrers.
Two aluminum pie plates, inverted and stapled (see diagram
2).
Cheese cloth.
Small cup (4 oz.) ice water.
Diagram
1 How to make a water bath
Diagram
2 Burner safety cover
Procedure:
1.
Divide class into groups of 4. Have students wear gloves
and goggles.
2.
Distribute sodium hydroxide/alcohol solution.
3.
Distribute melted fat.
4.
Add fat to custard cup. Place on water bath.
5.
Pour sodium hydroxide/alcohol solution into fat while
stirring with wooden stick.
6.
Continue heating and stirring until a small sample can
be completely dissolved in a test
tube filled half way with water.
7.
While stirring the solution have another student weigh
90g of salt into a container, using
a balance scale.
8.
Dissolve salt in 300ml of water.
9.
Pour the soap solution directly into the salt water.
The soap will separate and float.
10.
Using a rubber band place cheesecloth over another jar.
Pour the salt solution and soap through the cheesecloth.
Allow solution to drain. Pour 4 oz. of ice water on
soap
to remove the salt.
11.
Gently squeeze excess water from the cloth. Spread out
the cheese cloth to allow the soap to dry. Some soap
will dry faster than others, allow 1 to 3 days.
12.
Wash hands with soap and water. Avoid contact with eyes.
Activity
2: Testing the Soap
Materials:
1.
Homemade soap
2.
Various commercial soaps and detergents, i.e.. liquid
dish detergent, bar soap, soap flakes (Borax), powdered
laundry detergent, etc.
3.
Small clear containers to hold 50ml of sample.
4.
Test tubes (2 per test solution).
5.
pH paper and/or phenolphthalein (phenolphthalein
an acid/base indicator can be made from Ex-Lax tablets.
Grind one tablet and mix with one liter of luke-warm
water).
6.
Calcium chloride (available at supermarkets and
hardware stores as Driveway Heat or ice melt)
and Epsom salt (magnesium sulfate).
For
the class:
The
students will test their soap products using hard water.
( Hard water is that which contains Ca and Mg ions.)
To make water hard add � teaspoon of both calcium chloride
and epsom salt to two liters of water.
NOTE:
Since your water supply may be "hard", it
might be a good idea to use deionized water to make
all solutions for this activity. You can usually purchase
this inexpensively in a supermarket. Many people buy
deionized water for use in steam irons.
Procedure:
Dissolve
1g of test soap in 50 ml of luke-warm water.
Pour
10ml of each solution into either a test tube or a small
clear container. Into a similar container pour10ml of
plain water to act as a control.
3.
Test each sample with both pH paper and phenolphthalein.
4.
Add 5 drops of cooking oil to the test tube. Shake.
Record observation.
5.
In another test tube add 10ml of soap solution. Add
5ml of hard water. Shake.
Using a ruler measure the amount of foam created by
each sample.
Worksheet
Solution
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pH
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phenolphthalein
|
emulsion
|
foam
(cm)
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Teacher
notes:
- Enter
the solution number in column 1
- Using
pH paper will allow students to determine pH between
1 and 14
- Phenolphthalein
will turn the solution a shade of red if the pH is
above 8.5
- For
the emulsion column have students describe the conditions
within the test tube. For example, did the oil mix?
Has the solution become cloudy? Is there a layer of
foam? Is there a layer of scum on top of the water?
- Have
students measure the amount of foam above the water
line with a ruler.
Safety
Rules for the Home/School Chemistry Lab
- Work
with an adult.
- Wear
eye protection.
- Do
not touch your eyes or face while doing an experiment.
- When
something spills, clean it up immediately.
- Label
all containers with the name of the content.
- When
you have finished an experiment, put all equipment
away.
- Before
leaving your lab area, wash your hands.
This experiment is courtesy of 
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