| MadSci Network: Chemistry |
Ok Ill try and keep this simple. A solvent by definition is a
substance in which something can be dissolved. The thing that is dissolved
in the solvent is called the solute.
For example when you dissolve salt in a glass of water, the salt is the
solute and the water is the solvent.
Usually people think of solvents as things like nail polish remover, which
is the chemical acetone, or cleaners such as methylated spirits, which is
a mixture of methanol and ethanol. We commonly consider these chemicals as
"solvents" because they dissolve things that water usually doesn't,
just like acetone removes the paints off your nails but water won't.
The reason why these solvents remove the paints but water doesn't is
simply explained by a simple chemistry phrase, "like dissolves like".
Which means the paint on the nails , or the gluely mess on the back of
stickers that you can remove with methylated spirits, is chemically just
like the solvents themselves, and not like water, most of these solvents
are very non-polar, or uncharged. The best example of this is petrol, or
gasoline, it is very non-polar and totally unlike water, thats why it
doesnt mix with water at all, they are not "alike".
Chemically salt and water are similar too, they both are charged (think
can conduct electricity) thats why salt dissolves in water but not in nail
polish remover.
Ok so thats solvents, detergents are different because they are chemicals
have both a polar(or charged) section and a non-polar(or uncharged)
section. They are usually long thin molecules that have a charged end and
non charged tail, think of it like a matchstick, the head is charged and
likes to be in water, the end of the match is non-polar and wants to be in
a non-polar solvent like petrol or oil.
How detergents work to dissolve oil and grease for example when washing
dirty dishes is that the oily dirt is surrounded by the detergent, with
the non-polar end of the molecule surrounding the oily dirt. The other end
of the detergent points away from the oil and sits in the water where it
likes to be. So this clumps all the oilly dirt into "packets" called
micelles and they can be washed away.
A good picture of a micelle can be found at this web site
well I hope that helps
David Barker
Try the links in the MadSci Library for more information on Chemistry.