# Salt and freezing point

1. Dec 16, 2004

### MercuryRising

im confused...
we add rock salt to ice cream to lower freezing point. but how dose that help in making ice cream?
and when we add salt to the snow on the streets in order to melt them, dosent that also lowers the freezing point? dosent that makes the snow harder to melt???
thanks

2. Dec 16, 2004

### cyby

Adding salt to the road does indeed lower the freezing point of water. Simpler explained, as a result, water would freeze say, at -1 or -2 C instead of 0 C, and some of the snow/ice would melt at the prevailing temperature.

So actually, it makes the snow easier to melt....

Although I do not know how salt makes ice cream easier to make...

3. Dec 16, 2004

### Cantari

Since adding salt to the water lowers its freezing point, it is easier to make ice cream like that since the water can get colder.

4. Dec 17, 2004

### chem_tr

Raoult's law deals with these properties; boiling point elevation and its reverse effect, i.e., melting point decrease can be calculated by applying some formulae.

5. Dec 28, 2004

### r3dxP

Since the road part was explained nicely, no comment on that.
For the addition of salt to ice cream, I have done an experiment myself in school and made some vanilla icecream . I am unclear on how your experiment was designed, but procedure I used at my school was to add a shlt of salt into a big ziplock bag of ice(thus causing the ice to melt, but maintaining the temperature below 0 due to the colligative properties), then add a bag of melted vanilla icecream inside the salted ice bag, and wait for the vanilla icecream material to freeze. This occurs because the salted ice water probably is -5 degrees celcius or below 0 degree celcius anyhow, and the vanilla incecream material probably has a freezing point around 0, and this will cause the vanilla icecream to freeze, (not completely rock solid but with an icecream texture). This shows you how effective colligative properties are and allows you to make icecream on your own, rather than using machines to maintain a constant temperature below 0.
If you are thinking.. "why not put the vanilla icecream mixture into the freezer and freeze it, because it will freeze the mixture like a rock solid thing, which you do not want and will not have the rich texture of good icecream.

6. Dec 28, 2004

### GCT

If the freezing point of the substance is decreased the solid, willl now melt at the same temperature in which the non-mixture did not.