why does ice melt faster in water than salt water

Wow, where to start? First, I assume that by "water and ice" you meant "water and salt", otherwise it doesn't connect with the rest of your discussion. Let's start with the obvious parts based on familiar facts. If salt tended to stabilize ice more than water, by the fancy mechanism you describe, adding salt to ice would help keep it frozen. Somebody better tell the Highway Department, because they've been using salt to
ice all these years. Working our way toward slightly less familiar facts, the mechanism you describe would only work if the salt was actually in the ice, helping line up those water molecules. However, virtually none of the salt goes in to the ice. You can check this by partially freezing some salt water. You'll find that the non-frozen liquid is saltier than what you started with, because salt was from the ice.


I'm trying to see if there is any grain of truth in what you've written. It is true that dissolving table salt in water will lower the temperature of the water, because it takes energy (more precisely, enthalpy) to pull those ions apart. That could help freeze the water. However, that effect amounts to only about 0. 9 K cooling for 1 M salt concentration. (That cooling is temporary and has no effect on the freezing time for the salt water if you let it stand at room temperature before putting it in the freezer. ) The same 1M NaCl lowers the freezing point of water by about 3. 7 K, so it still needs to cool than plain water before it freezes, even if you didn't let it reach room temperature first.


So I have to conclude that everything you wrote about the science of water and salt is incorrect. Is it possible that your glass of salt water froze first? Maybe- freezers don't cool evenly, some spots already have frost, some are in good contact with metal, so it takes a lot of care to check whether the result depended on details of placement, etc. However if you got the water really salty, stirring in NaCl until no more would dissolve, the water wouldn't freeze until it was cooled to -21. 1 C. Ordinary home freezers don't usually get quite that cold, so unless you have a very good freezer on the coldest setting you would have seen it freeze. For anybody who wonders who is right: do the experiment yourself. Mike W. (published on 09/11/2009) Lara Baxley, Bakersfield College, California answered on December 8, 1999 An ice cube does melt much faster in tap water than in salt water.


The reason has to do with different rates of conduction of heat from the surrounding water to the ice cube. When an ordinary ice cube melts in a regular glass of water, you have to remember that cold water (like the water from the ice cube) is actually denser than warm water (like the surrounding water in the glass). This is because cold water molecules have less energy and are a tiny bit closer together than molecules in warmer water. So as the ice cube melts, the cold water coming from it sinks to the bottom of the glass and the warm water from the bottom comes up to take its place. The water in the glass is therefore constantly moving, warming the ice cube by something called 'convection currents. ' But salt water is much denser than tap water, warm or cold, because of the salt in it.


So when you put a freshwater ice cube into a glass of salt water, the cold water coming from the melting ice cube doesn't sink at all. Instead, the dense salt water stays at the bottom of the glass and the cold less-dense fresh water floats on top. Without any convection currents to carry the cold water away from the ice cube, the ice cube sits in relatively cold water and melts much more slowly. Add to or comment on this answer using the form below. Note: All submissions are moderated prior to posting. If you found this answer useful, please consider making a to science. ca.

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