Science - Chemistry - Organic Chemistry - 8 Soaps
(P7173300)
8.1 Production of soap
Experiment by: Anouch
Printed: Feb 25, 2014 2:26:54 PM
interTESS (Version 13.12 B214, Export 2000)
Task
Task
How can soap be produced?
Prepare soap from fat or stearic acid.
Use the space below for your own notes.
Logged in as a teacher you will find a button below for additional information.
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Additional Information
Learning objectives
• Soaps can be produced from long-chain carboxylic acids or from fats by the
addition of alkali liquor.
• Soaps must therefore consist of alkali salts of fatty acids.
Notes on set-up and procedure
Preparation:
Prepare concentrated caustic soda and 25% caustic soda (34 g NaOH to 100 ml with
water) ready for use. Have the eyewash bottle at hand.
Margarine or hard vegetable fat are suitable fats.
Remarks on the students experiments:
Both stearic acid and the fat must only be heated in a way that they just melt. At
higher temperatures, the caustic soda tends to splash strongly.
Hazard and Precautionary statements
Sodium hydroxide:
H314:
P290:
P280:
Causes severe skin burns and eye damage.
May be corrosive to metals.
Wear protective gloves/ protective clothing/ eye protection/
face protection.
P305 + P351 + P338: IF IN EYES: Rinse cautiously with water for several minutes.
Remove contact lenses, if present and easy to do. Continue
rinsing.
P309 + P310:
IF exposed or if you feel unwell: Immediately call a POISON
CENTER or doctor/physician.
P301 + P330 + P331: IF SWALLOWED: rinse mouth. Do NOT induce vomiting.
P501:
Dispose of contents/ containers to be collected by a licensed
contractor in accordance with national and local regulations.
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Ethanol:
H225:
P210:
P233:
Highly flammable liquid and vapour.
Keep away from heat/sparks/open flames/hot surfaces. - No smoking.
Keep container tightly closed.
Hazards
• Sodium hydroxide is highly corrosive. Wear protective gloves!
• When caustic soda is added to the melt, splashing can occur. Wear protective
glasses!
• Denaturated alcohol is highly inflammable. When handling, extinguish all open
flames!
Notes
The "saponification" of fat which is carried out here corresponds to the classical
procedure for producing soap. According to old recipes it can also be carried out
using plant ashes (potash).
Remarks on the method
Sharing the work in groups can be particularly motivating here, as from different
starting materials the same final product is obtained. The final product exhibits very
different properties compared to those of the starting materials. The various
experimental procedures can be presented by the work groups and the fact that the
results are identical can be fruitfully discussed.
Waste disposal
• Transfer the contents of the test tubes to the beaker and filter them. Pour the
filtrate into the container for organic liquids.
• Put soap and fat residues in the normal waste.
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Material
Material
Material from "TESS advanced Chemistry Set Organic Chemistry, CH-4"
(Order number 15304-88)
Position No. Material
Order No. Quantity
1
Support base, variable
02001-00
1
2
Support rod, l = 370 mm, d = 10 mm
02059-00
1
3
Spoon spatula, special steel
33398-00
1
4
Glass beaker DURAN®, short, 250 ml
36013-00
1
5
Test tube brush w. wool tip, d = 25 mm
38762-00
1
6
Test tube holder, up to d = 22 mm
38823-00
1
7
Wire gauze 160 mm x 160 mm, ceramic cen.
33287-01
1
8
Test tube, 180x18 mm
37658-10
(3)
9
Wash bottle, plastic, 250 ml
33930-00
1
10
Rubber stopper, d = 22/17 mm, without hole
39255-00
1
11
Glass rod, boro 3.3, l = 200 mm, d = 6 mm
40485-04
1
12
Rubber gloves, size 7
39325-00
1
13
Test tube rack for 12 tubes, holes d = 22 mm, wood
37686-10
1
14
Ring with boss head, i. d = 10 cm
37701-01
1
15
Graduated cylinder, 10 ml, plastic
36636-00
1
16
Protecting glasses, clear glass
39316-00
1
Chemicals, additional materials
Position No. Material
Order No. Quantity
Bunsen burner /DIN/, nat.g., w. cock
32168-05
1
Safety gas tubing, DVGW, sold per metre
39281-10
1
Sodium hydroxide, flakes, 1000 g
30157-70
Stearic acid, 250 g
30228-25
Denaturated alcohol (spirit for burning), 1000 ml
31150-70
Water, distilled, 5 l
31246-81
Fat
Material required for the experiment
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Setup
Setup
Hazards
• Sodium hydroxide is highly corrosive. Wear protective gloves!
• When caustic soda is added to the melt, splashing can occur. Wear protective glasses!
• Denaturated alcohol is highly inflammable. When handling, extinguish all open flames!
Setup
Set up the stand as shown in Fig. 1 to 4. Fasten the support ring to the support rod and lay
the wire gauze on it. Adjust the height of the support ring, so that the flame of the Bunsen
burner just reaches the wire gauze.
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Put 3 spoonfuls of fat in the beaker. Put the beaker on the wire gauze (Fig. 5).
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Fig. 5
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Action
Action
Procedure
Heat the beaker carefully with a small flame so that the fat just melts. Add 10 drops
of denaturated alcohol (Fig. 6) and 5 ml of distilled water (Fig. 7). Add to this mixture, little
by little, 10 ml of 25 % caustic soda (Fig. 8) and heat under stirring with the glass rod for further
10 minutes (danger of splashing).
Fig. 6
Fig. 7
Fig. 8
During this time, replace evaporated water by the careful addition of distilled water. Allow the
beaker to cool (Fig. 9+10).
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Fig. 9
Fig. 10
Put a spoonful of stearic acid in a test tube (Fig. 11), add 3 ml of denaturated alcohol (Fig. 12)
and 5 ml of distilled water (Fig. 13).
Fig. 11
Fig. 12
Fig. 13
Warm the mixture briefly, then add 3 ml of concentrated caustic soda (Fig. 14+15). Be careful
since splashing may occur during the addition!
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Fig. 14
Fig. 15
Heat carefully, under slight shaking, for 3 minutes, without bringing the liquid to boiling. Put
the test tube in the test tube stand when it has cooled (Fig. 16).
Fig. 16
Pour about 1 ml of the upper phase into a second test tube (Fig. 17). Add distilled water up
to a height of about 5 cm. Stopper the test tube and shake it vigorously (Fig. 18).
Fig. 17
Fig. 18
Use the spoon to collect a little of the substance which has precipitated out in the beaker
(Fig. 19) and put it in another test tube (Fig. 20). Add distilled water as above, stopper the test
tube and shake it vigorously (Fig. 21).
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Fig. 19
Fig. 20
Fig. 21
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Results
Results
Note your observations.
Conversion of fat with caustic soda:
Conversion of stearic acid with caustic soda:
Effect of water on the reaction product:
Conversion of fat with caustic soda:
The fat melts on heating. On the addition of denaturated alcohol and caustic soda,
an emulsion is first formed and after some time the fat dissolves. On longer heating,
a whitish-coloured substance precipitates out in the top part, while a homogeneous
liquid is formed in the lower part.
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Conversion of stearic acid with caustic soda:
The stearic acid also melts on heating and here also an emulsion is first formed from
which a whitish-coloured substance separates. The emulsion changes in the course
of the reaction to a homogeneous liquid.
Effect of water on the reaction product:
When the white reaction products from the two parts of the experiment are shaken
with water, they each cause frothing; soap bubbles are formed.
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Evaluation
Evaluation
Question 1:
Draw conclusions from your observations.
Fats and stearic acid are only sparingly soluble in caustic soda. They form an emulsion
on the addition of denaturated alcohol. Stearic acid is neutralized by caustic soda.
Caustic soda reacts both with fats and with stearic acid to form soap.
Question 2:
Fats are glyceryl esters of long-chain carboxylic acids. Which reaction must have taken place
in the first part of the experiment?
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The ester was split by the caustic soda. An alcohol (glycerol) is re-formed, as well as
the sodium salt of the fatty acid.
Question 3:
Which information on the composition of soap can you draw from the experimental work?
As in a neutralization reaction, a salt (and water) is formed, soap must be a salt (alkali
salt) of a fatty acid, in this case of stearic acid. This corresponds also to the result of
ester splitting, as here also the sodium salt of the fatty acid contained in the fat is
formed.
Question 4:
Formulate the equations for both reactions.
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(C17H35COO)3C3H5 + 3 NaOH → 3 C17H35COONa + C3H5(OH)3
C17H35COOH + NaOH → C17H35COONa + H2O
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