Salt and Ice

[Target1911]

If your side walk is covered in ICE, you put rocksalt on it to melt the ice.....

HOWEVER.......

when making homemade icecream you must use rock salt on the ice to make it cold enough to make the ice cream and if your cooler is full of ice and cans of soda, you can put rock salt on the ice to keep them colder and may even freeze and bust the cans of soda.

Why is it that the same thing that is used to MELT ice also is used to make it colder?

[killerfly128]

If your side walk is covered in ICE, you put rocksalt on it to melt the ice.....

HOWEVER.......

when making homemade icecream you must use rock salt on the ice to make it cold enough to make the ice cream and if your cooler is full of ice and cans of soda, you can put rock salt on the ice to keep them colder and may even freeze and bust the cans of soda.

Why is it that the same thing that is used to MELT ice also is used to make it colder?

Rock salt only allows the water to be liquid at a lower temp than it would be able to by itself ... answer your question?

[Target1911]

That makes sence..... on the other end of the question, why does it make it so cold that it will freeze a can of soda to the point of busting?

[psijac]

Salt makes ice colder the same way salt makes a snail or slug colder. Putting salt in a cooler makes the ice turn to water but stay the same temp. it has more surface area to make contact with the soda cans and heat transference occurs more rapidly.

[The Annoyed Man]

Science!!

[Keith B]

That makes sence..... on the other end of the question, why does it make it so cold that it will freeze a can of soda to the point of busting?

As others have said, the salt in the water actually lowers the freezing point of water, normally 32º F (0º C). Depending on the ratio of salt to water, the freezing point will be much lower. A 10-percent salt solution freezes at 20º F (-6º C), and a 20-percent solution freezes at 2º F (-16º C). So, with the freezing point of soda being around 32º F, with the water temp being so much lower, the soda will freeze extremely solid to the point of busting. The same process is what makes ice cream in the home-made freezer freeze.

[The Annoyed Man]

This is also why ocean water must be cooled beyond what is necessary for fresh water before it will freeze.

[chabouk]

To elaborate on the ice cream maker: the ice you put in the tub isn't 32F, it's the temperature of whatever freezer it came out of. But, the water that forms as it melts will only be 32F or slightly warmer, and it's that water that serves to transfer heat out of the inner container so the liquid will freeze. By adding salt, the water can be almost as cold as the ice (as noted, 20F or lower). Without salt, the ice cream mix can't freeze (unless it's freezing point is 35F or higher).

[Target1911]

I knew i could count on this site once again for the answers I need .
Thanks

[killerfly128]

Science!!

[roberts]

Magic for sure. Think about the energy required for the solid-liquid phase transition.

[mctowalot]

Just a side note: do NOT eat the yellow slush!

[MoJo]

Just a side note: do NOT eat the yellow slush!

I don't know look at this - - - YELLOW SNOW

[Dan20703]

Okay people, time for a science lesson. The energy to transform water from a solid (32 degrees) to a liquid (32 degrees) or vice versa will require about 80 calories per gram of ice. The salt melts the ice by lowering the freezing point and draws the energy for liquification from anything touching it (ice, beer cans or ice cream unit). This is also known as the enthalpy of fusion. (God I can't believe I remember this from thermodynamics in college). In a closed system the temp will drop initially (ice cream maker) while an open system (sidewalk) the ice will just melt. Hope this confuses everyone.