Melting Salt-Ice
Most recent answer: 10/22/2007
Q:
what happens when ice containing 20ml of salt is melted with a bunsen burner?
- Anonymous (age 14)
- Anonymous (age 14)
A:
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.
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)