How Salt Melts Ice

Materials & Equipment:

Water, salt, 2 pie pans, a freezer

Procedure:

Setup

Setup

Fill each pan with water to about 2/3’s capacity. Place the pans on your freezer shelf, then wait for the water to freeze. After the water has turned to ice, set your pans side by side, and choose one to sprinkle with sea salt.

Results:

The salted ice will begin melting immediately. This is very similar to the way that our cities brine roads in anticipation of a snow or ice event. The science behind this method? Salt lowers the freezing (and also melting) point of water; therefore, the outside temperature must decrease significantly in order to maintain the salted ice.

Results - Salted Ice

Results – Salted Ice

Results - No Salt Added

Results – No Salt Added

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2 thoughts on “How Salt Melts Ice

  1. You didn’t say HOW salt melts ice…. This explanation is short and to the point:

    The primary difference between water and ice is the speed at which the molecules move. In water, the molecules move more rapidly than in ice. The temperature of the water is changed by adding or removing heat. As heat is removed, the water molecules slow down. At the freezing point, the motion of the molecules is slow enough that the water becomes ice.

    When salt is added to water, the salt and water molecules stick together, <ore heat then must be removed to slow down and separate the combined salt and water molecules. The removal of the additional heat is required to freeze the salt-water combination. This means that the temperature at which it freezes is below that of pure water.

    Antifreeze uses the same principle to keep the water in your car from freezing in the winter. Spreading salt over roads prevents melting snow from freezing into ice and causing hazardous road conditions.

    For similar reasons, the addition of salt to water increases the boiling point of the water: more heat must be added to make the larger combined salt plus water molecule move fast enough to boil than must be added to make plain water boil. The result is that the temperature of the boiling salted water is higher than that of plain water.

    Salt is not the only substance which lowers the freezing point of water. In fact, anything that can be dissolved in water will have the same effect.

    http://www.pa.msu.edu/sciencet/ask_st/030492.html

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