Re: Why does an ice cube melt faster in freshwater than one does in saltwater?

An ice cube melts at 32 degrees F, which is the same as 0 degrees Celcius.
When you put that ice cube into water, it quickly cools the water around
it (which is why we put ice in soda in the first place).  Fresh water 
can only be cooled to 0 degrees, and since it can always find some heat
from someplace else (like sunlight, or someone's hand on a glass, or being
in a warm room), it never quite makes it to 0, so the ice melts.

Salt water, however, can be cooled much lower than 0 degrees.  Since it can
be colder, the ice cube does not melt as fast.