2. 2
What is Soap?
• Soaps are sodium or potassium salts of long-chain fatty
acids. The general formula of a soap can be written as:
RCOO-
K+
or RCOO-
Na+
.
• Where R is alkyl group, can be saturated or unsaturated
which is consist of 12 to 18 carbons atom.
Example:
Sodium palmitate, CH3(CH2)14 COO-
Na+
Potassium stearate,CH3(CH2)16COO-
K+
Note: State several types of alkyl group
3. 3
Soap Preparation
Process
• Soap can be made from animal fats
and vegetable oils. They are prepared
by hydrolysing fats or oils under
alkaline condition. The reaction
is called saponification.
• Saponification process involves boiling fats or oils with
concentrated sodium hydroxide, NaOH solution to
produce gylcerol and soaps.
4. 4
General Equation
Oil/ fats + alkali Soaps + water + glycerol
• The three alkyl group can be the same or different groups.
• When concentrated potassium hydroxide, KOH solution is
used instead of concentration sodium hydroxide, NaOH
solution, a potassium soap, potassium palmitate,
CH3(CH2)14COO-
K+
is formed.
Note: Show the chemical reaction of making soap
Glycerol
Oil/fats
5. 5
What is Detergent
• Any cleaning agent that is
not a soap is a detergent.
• Detergent are usually made
from synthetic resources such
as petroleum fractions.
• Detergents are usually sodium salts of sulphonic
acid.
6. 6
Preparation of detergent
• During the preparation of detergents, long-chain
hydrocarbon obtained from petroleum fractions is
converted into an organic aid through a series of
steps.
• The organic acid is then neutralized with sodium
hydroxide, NaOH solution to produce a detergent.
• The summarizes steps involved in the preparation of
sodium alkyl sulphate and sodium alkylbenzene
sulphonate as follows:
10. 10
STEP 1
• When soap or detergent is
added to water, it reduces the
surface tension of water. This
increases the wetting ability of
water. Therefore, the surface of
the cloth is wetted thoroughly.
• The hydrophobic part of the
soap or detergent anion is
soluble in the grease. The
hydrophilic part is soluble in
water.
12. 12
STEP 3
• The droplets do not
coagulate and redeposit on
the surface of the cloth due
to the repulsion between
the negative charges on
their surface.
• These droplets are
suspended in water,
forming an emulsion.
Rinsing washers away
these droplets and leaves
the surface clean.
13. 13
How Water Hardness
Affects Cleaning Action
• Although soap is a good cleaning agent,
its effectiveness is reduced when used
in hard water. Hardness in water is
caused by the presence of mineral salts
- mostly those of calcium (Ca) and
magnesium (Mg), but sometimes also
iron (Fe) and manganese (Mn).
• The mineral salts react with soap to form
an insoluble precipitate known as scum.
• 2Na+
(R-COO)-
(aq) + Ca2+
(HCO3
-
)2(aq) →
2Na+
(HCO3)-
(aq) + Ca(R-COO)2(scum)
14. 14
Comparison between a soap and
detergent
Cleaning agent Soap Detergent
Effectiveness
Effective cleaners
in soft water
Effective cleaners in
both hard and soft
water
Formation of
Scum
Form scum in hard
water
Do not form scum in
hard water
Formation of
precipitate
Form precipitate in
acidic water
Do not form precipitate
in acidic water
Sources Natural resources Synthetic resources
Effect to
environment
Biodegradable Non- biodegradable
