I don't really know what you're looking for here, but the best answer I can give you is: it melts.
It's
not clear how the salt is "in" the ice in your example. When water
freezes, it excludes almost all the salt, leaving behind either little
pockets of very salty brine or, at low enough temperature, little salt
crystals. Any salt on the ice will make it begin to melt at a somewhat
lower temperature than freshwater does. The initial melting temperature
will be -21 degrees C if there are some actual salt crystals around. If
your 20 ml of salt is on a smallish block of ice, the whole block will
melt at -21 C, before all the salt even dissolves. If you have a big
block of ice, the salt water will start to get diluted, more like pure
water. How warm it has to get before the last bit of ice melts depends
on how much ice there is, because that's what determines how dilute the
saltwater gets. If your 20 ml of salt is on a very big block of ice, it
won't finish melting until it's almost at the freezing point of pure
water, 0 degrees C. At any temperature in between, some of the water
will be in the salt solution and some in the frozen ice.
Perhaps
what you're planning is to compare what happens to the temperature of
the ice plus salt with what happens to the temperature of pure ice as
they're heated by the burner. What you may find is that when you heat
the pure ice, the temperature stays stuck near 0 deg C until all the
ice has melted, then starts to rise. For the salt plus ice, the
temperature may stay stuck around -21 deg C until all the salt is
dissolved, then rise slowly until all the ice is melted, then rise
quickly. Actual experimental results are likely to be a little less
clear, because parts of your material will be at different temperatures
than other parts and the salt solutions may not mix well, etc.
-Tamara and Mike W.
(published on 10/22/2007)
