How do soaps work

1. How Does Soap Work?
“Like dissolves like”

2. Polar Molecules
•Some Molecules, such a H
2
O, are
POLAR -meaning that they have a
(slightly) positive end and a (slightly)
negative end like a battery.
•Polarity is the result of unequal sharing
of electrons in a bond causing one atom
in the bond to be more negative than
the other.

3. Non-Polar Molecules
•Other Molecules, such as
hydrocarbons, or symmetrical
molecules (O
2
, N
2
, CO
2
) are non
-polar,meaning that their electrons are
shared more or less equally and there
is no positive end or negative end.

4. “Like dissolves Like”
•Polar things interact with Polar things,
and repel non polar things
–Ex: Water (polar) will dissolve salt (ionic),
but will not mix with oil (non polar).
•Non Polar things interact with non Polar
things and repel Polar things
–Ex: Kerosene (non polar) will mix with oil
(non polar) but not water (polar)

5. Hydrophilic and Hydrophobic
•“Hydro” – water
–“phobic” – doesn’t like! (non-polar)
–“philic” – does like (polar)
•Things that interact with polar water
molecules are water-loving or hydrophilic.
Hydrophilic substances include Salts,
alcohols, and anything with polarity.
•Things that don’t like water are water-hating
or hydrophobic. Hydrophobic substances are
oils, grease, and anything Non polar.

6. Long chain hydrocarbons
•Long chain hydrocarbons such as
alkanes and alkenes are NON-POLAR
Covalent molecules.

7. Alkanes – non-polar

8. Alkanes with stuff added on…
•Adding functional groups such as
alcohol (-OH) or Carboxyl (COOH),
causes one part of the molecule to
become Polar
–The rest of the molecule is still non-polar,
especially if it’s a really long chain

9. Saponification reaction
•Soap is made by reacting a fatty acid
with a base
•This breaks the Carboxyl bonds to form
a soap (with a polar end) and Glycerol

10. Soaps
•A soap molecule has a Polar
hydrophilic ‘head’ and a Non
polar hydrophobic ‘tail’
•The head will interact with
the polar water molecules
and the tail will interact with
the grease molecules.
•This means a soap can
interact with both oil and
water.

11. Soaps
•In this way, the soap molecules can
cause grease molecules to dissolve into
the water, by forming micelles which
allow small particles of grease to be
lifted up into the water.

12. Micelle

14. Soap dissolves grease
•The non-polar part of soap dissolves
the grease,
•The other end dissolves salts, polar
stuff and associates with water
•Voila! Clean dishes!

15. Words you should understand
•Polar / polarity
•Non-polar
•Hydrophilic
•Hydrophobic
•Micelle