Re: Which boils water with coffee mix or water.Why?

First, let me point out something about how you've phrased the question,
and then I'll try to answer it.  It is better to think of the water not as
boiling 'faster or slower' but as boiling at a lower or higher temperature.
 If you take a liquid with a boiling point less than water, here's what
will happen.  When you put the container onto the heat source, heat energy
begins to flow into the container and liquid.  As both pick up more heat
energy, they begin to get warmer.  A certain amount of heat energy is being
added to the container and liquid in each time unit - if you leave a pot on
a burner, it gets warmer every second.  Different liquids need a different
amount of heat per unit time in order to heat enough to reach a boil.  So,
while you're right in your observation that it "takes longer" for salt
water to boil than water, it's better to think of the salt water as having
a higher boiling point.

Water is a strange liquid in a lot of ways.  If you've ever spilled rubbing
alcohol or nail polish remover (acetone) you probably noticed how fast it
evaporates, especially compared to water.  Water also has a stronger
surface tension than most liquids.  Both of these effects come from the
molecular properties of water.  You can picture a single molecule of water
as a boomerang, where the middle part has a slight + charge, and the ends
have a slight - charge.  You've probably also heard the term 'opposites
attract' - that's exactly what is happening in water.  If you could see
something as small as a molecule, you'd notice that the middle of the
'boomerangs' line up with the ends of other water molecules.  That slight
attraction keeps water molecules from flying off into the gas above it
(this is what evaporation and boiling are).

When you add salt to the water, it dissolves into a sodium atom with a
strong + charge and a chlorine atom with a strong - charge.  These can be
imaged as balls with a strong charge.  The ball shapes can get in between
the boomerangs, and because it has a strong charge it makes an even
stronger set of attractions to the water molecules.  This means it's even
harder for the water molecules to pop free into the gas above it, making
the boiling point higher.

You observed that coffee crystals added to water drops the boiling point. 
There are lots of different chemicals in coffee, with lots of different
properties.  That makes it hard for me to tell exactly what's happening at
the molecular level, but we can figure out something from your observation.
 With the logic we used above, we know that if the molecules strengthen the
links between water molecules the boiling point goes up.  So, the molecules
in the coffee crystals must be weakening the attractions between the water
molecules, dropping the boiling point (or in your words, making it boil
faster).

I hope this helps!
Kevin Davies