I want to know what is the efect of salt (NaCl) in ice... I mean why in winter salt is used to melt the ice in roads... :)

If I tell you that salt-water has a lower freezing point than pure water (as low as -21 Celsius, depending on concentration), then can you use that to answer the second part of your question?

Thank you Capuchin... now I understand that... thank you very much you explained that very good...

**Added sentence -- Please check this site --

How does salt melt ice? (http://ask.yahoo.com/20030619.html)

The melting point of ice is 0 degrees Celsius. The effect of salt on ice is that salt changes the melting point of ice (to -4 degrees c) therefore, the ice will melt in a lower degree if salt added.

This is to WonderGirl's question also.

When a solid is dissolved in a liquid, three things happen (also happens when 2 liquids combine):

The freezing point goes down.
It is more difficult for the molecules of the liquid to nessle up next to each other when it gets cold, because the extra ions are getting into the matrix.
e.g.. Salt used to melt ice.
e.g.. Antifreeze in your car's radiator.

The boiling point goes up.
The dissolved ions add to the forces keeping the liquid - well liquid.
e.g.. Sugar dissolved in water to make candy is boiled until the sugar melts at 320F. The sugar increased the boiling point at least up to there, or the water would boil away before the sugar melts.
e.g.. Antifreeze in your car's radiator.

The density increases.
The dissolved ions can slid into places that remain "empty" with just the pure liquid.
In my Chem class we took 50 mL of water and 50 mL of alcohol and poured the together. We ended up with less than 95 mL combined.
e.g.. Antifreeze in your car's radiator.

I didn't post a question. That was a clickable link to answer her question.

Salt water can remain liquid down to -21°C (-6°F). Brine - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Brine)