Lab
Soaps and Detergents: Cleaning up with Chemistry
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University:
American Baptist College -
Course:
CIT370 | Database Design and Processing Academic year:
2019
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35
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CHEM 258
CHAPTER 4
Surfactants
Soaps and Detergents:Cleanning up with Chemistry Outline
Surface tension
How detergents affect surface tension and how they
clean clothes and other household goods?
Similarities and differences between soaps and
detergents.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
2 Surface Tension
•
Place a small object like a needle or a paper clip very gently on the
surface of a glass of water.
Instead of sinking, the metal seems to float.
Actually, it is resting on the water’s surface, supported by
phenomenon known as surface tension.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
a
3 Surface tension in action
Have you ever seen an insect skimming across the surface of a
puddle or pond?
Surface tension allows insects to walk over water and tacks to rest
on its surface.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
4 Density
•
Density: mass per unit of volume
•
Density of water: 1.0 g/ml
•
Anything that’s denser than water:Sinks
•
*metals and concrete
Anything that’s less dense than water:Floats
*fats and oils, boats float because the air trapped
inside their hulls gives them an avarage density less
than water.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
5 Surface tension
Metal tack is denser than water, no trapped air but the
tack is supported in a small dent on the water’s surface.
Same phenomenon supports an insect’s feet as it walks
across a pond.
http://www.youtube.com/watch?v=kx02qT2p5uk
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
6 Surface tensIon
Surface and Interfacial Tensions
In the liquid state, the cohesive forces between adjacent molecules are well
developed.
For the molecules in the bulk of a liquid
They are surrounded in all directions by other molecules for which they have
an equal attraction.
For the molecules at the surface (at the liquid/air interface)
Only attractive cohesive forces with other liquid molecules
which are situated below and adjacent to them.
The net effect is that the molecules at the surface of the
liquid experience an inward force towards the bulk of the
liquid and pull the molecules and contract the surface with
a force F .
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
7 Surface tensIion
To keep the equilibrium, an equal force must be applied to
oppose the inward tension in the surface.
Thus SURFACE TENSION [γ ] is the force per unit length
that must be applied parallel to the surface so as to
counterbalance the net inward pull and has the units of
dyne/cm
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
8 Under the surface,
intermolecular attractions pull on
individual molecules in all directions
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
= intermolecular
attractions
8/8/2022
9 At the surface,
pull on the molecules is laterally and downward;
there is negligible intermolecular attractions
above the molecules (from the medium above, such as
air).
SO, the net force on surface molecules is downward.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
= intermolecular
attractions
10 The result of this downward force is that
surface particles are pulled down until
counter-balanced by the compression
resistance of the liquid:
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
11 CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
12 CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
13 Surface molecules are compressed
more tightly together,
forming a sort of skin on the surface,
with less distance between them
compared to the molecules below.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
14 This explains the characteristic rounded
shape that liquids form when dropping
through the air: The molecules are all
being pulled toward the center.
15
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022 Soap and detergent:SURFACTANTS
SURFACTANTS: Surface-active agents
These agents accumulate at surfaces and change their properties
sharply by lowering the SURFACE TENSION.
All detergents are SURFACTANTS.
Detergent: to wipe out, to clean
Soap: a particular kind of detergent
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
16 Soap and detergent:SURFACTANTS
Even a small amount of a surface active agent can
produce dramatic effects.
At a concentration of 0.1%, for example, soap lower
water’s surface tension by almost 70%.
http://www.youtube.com/watch?v=ciqNNRlS2yA berkeley
http://www.youtube.com/watch?v=Pe12NedfYC0 cork
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
17 Soap
•
A soap is a salt of a compound known as a fatty acid.
•
A soap molecule consists of a long hydrocarbon chain
(composed of carbons and hydrogens) with a carboxylic acid
group on one end which is ionic bonded to a metal ion,
usually a sodium or potassium.
•
The hydrocarbon end is nonpolar and is soluble in nonpolar
substances (such as fats and oils), and the ionic end (the salt
of a carboxylic acid) is soluble in water. The structure of a
soap molecule is represented below:
Sodium salts of the fatty acids containing from 10 to 18 carbons
make the best soaps.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
18 CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
19 Soap making
Natural
soaps are prepared by boiling lard or
other animal fat with NaOH, in a reaction called
saponification (Latin, sapo, soap).
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
20 How soap cleans
Soap cleans by:
Decreasing water’s surface tension, making it better
wetting agent,
Converting greasy and oily dirt into MICELLES that
become dispersed in the soapy water, and
Keeping the grease micelles in suspension, thereby
preventing them from coalescing back to large globules
of grease that could be redeposited on a clean surface.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
21 A soap micelle
•
A soap micelle: nonpolar (hydrophobic) hydrocarbon chains cluster in
the inside and polar (hydrophilic) carboxylate groups lie on the surface.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
22 A soap micelle
•
Micelle: A spherical arrangement of organic molecules in
water clustered so that their hydrophobic parts are
buried inside the sphere and their hydrophilic parts are
on the surface of the sphere and in contact with water.
•
When soap is mixed with water-insoluble grease, oil,
and fats, the nonpolar parts of the soap micelles
“dissolve” these nonpolar dirt molecules and they are
carried away in the polar wash water.
http://www.youtube.com/watch?v=kpRbnLZX_dI (3
glasses)
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
23 A problem:hard water
Soaps, will react with metal ions in the water and can
form insoluble precipitates. The precipitates can be
seen in the soapy water and are referred to as “soap
scum”.
This soap scum can form deposits on clothes causing
them to be gray or yellow in color.
To eliminate the metal ions in water, washing aids such
as washing soda (sodium carbonate) and borax (sodium
tetraborate) are added to the wash water. These
compounds would precipitate the metal ions,
eliminating most of the soap scum.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
24 Soaps
form water-insoluble salts when used in
water containing Ca2+, Mg2+, and Fe3+ ions (hard
water).
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
25 Synthetic Detergents
With the discovery of synthetic detergents, much of the
need for washing aids was reduced. A detergent works
similar to a soap, but does not form precipitates with
metal ions, reducing the discoloration of clothes due to
the precipitated soap.
Modern laundry detergents are mixtures of detergent,
water softeners, optical brighteners, stain removers,
and enzymes.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
26 Synthetic Detergents
The design criteria for a good detergent are:
a long hydrocarbon tail of 12 to 20 carbons.
a polar head group that does not form insoluble salts with
Ca(II), Mg(II), or Fe(III) ions.
The most widely used synthetic detergents are the
linear alkylbenzenesulfonates (LAS).
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
27 Synthetic Detergents
Detergents are structurally similar to soaps, but differ in the watersoluble portion. Three examples of detergents are shown below.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
28 Surfactant (or detergent) classification
According to charges:
A. Ionic
o
Anionic surfactants: the surface active part is anion (negative
ion ) e.g. Soaps (sodium stearate), sodium lauryl
sulfate,(sodium lauryl Sulphate) CH3(CH2)11 OSO3-Na+
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
29 SURFACTANT CLASSIFICATION
Anionic surfactants
They are the metal salts of long chain fatty acids as lauric acid.(Soap)
Sodium dodecyl sulfate or Sodium Lauryl Sulfate is used in toothpaste
and ointments
Triethanolamine dodecyl sulfate is used in shampoos and other cosmetic
preparations.
Sodium dodecyl benzene sulfonate is a detergent and has germicidal
properties.
Sodium dialkvlsulfosuccinates are good wetting agents.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
30 SURFACTANT CLASSIFICATION
Cationic surfactants:
The surface active part is cation (positive ion) e.g. quaternary ammonium
salts ,hexadecyl trimethyl ammonium bromide (cetrimide).
These are chiefly quaternary ammonium compounds. They have bacteriostatic
activity probably because they combine with the carboxyl groups in the cell
walls and of microorganisms by cation exchange, causing lysis.
Among the most popular antiseptics in this category are benzalkonium
chloride, cetylpyridinium chloride and cetyltrimethylammonium bromide.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
31 SURFACTANT CLASSIFICATION
B. Nonionic –
polyethylene oxide
-Sorbitan mono-oleate (Span)
- (Polysorbate 80 = Tween 80)
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
32 Synthetic Detergents
Also
additives for detergent preparations are:
• foam stabilizers.
• bleaches.
• optical brighteners.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
33 How Detergents clean?
When a detergent is added to water, a polar solvent, the
molecules form clusters, known as micelles, in which the
polar ends of the molecules are on the outside of the cluster
and the non-polar ends are in the middle.
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
34 How Detergents clean?
•
The cleaning action of detergents results from their
ability to emulsify or disperse water-insoluble materials
(dirt, oil, grease, etc.) and hold them in suspension in
water.
•
This ability comes from the molecular structure
detergents. When a detergent is added to water that
contains oil or other water-insoluble materials, the
detergent molecules surround the oil droplets. The oil
or grease is “dissolved” in the alkyl groups of the
detergent molecules while the ionic end allows the
micelle to dissolve in water.
As a result, the oil droplets are dispersed throughout the
water (this is referred to as emulsification ) and can be
rinsed away.
http://www.youtube.com/watch?v=Nxkjn-XhgE0
http://www.youtube.com/watch?v=ZMhyD-wUPjo emulsion formation
CHEM 258, Assoc. Prof.Öznur DEMİR ORDU
8/8/2022
35
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