Why Does Salt Melt Ice?
- Chemistry 101

Why does salt melt ice? Well...let's explore some basic chemistry.
Water will freeze and transform into ice at exactly 0 Celcius (32 Fahrenheit). However, with the introduction of salt, water will freeze at a lower temperature.

For example:
With a salt solution of 10%, water will begin to freeze at -6 Celcius. When you double the salt solution to 20%, freezing only begins at -16 Celcius.

Salt spreading techniques vary. Local governments create their own policies on which salt spreading techniques to use. However it is the temperature which plays the biggest role in how you de-ice your roadways.

Generally salt is spread on pavement at temperatures of 0 to -15.When the temperature drops below -15, salt becomes much less effective is a de-icing agent.At these temperatures it become necessary to coat the ice with a salt-gravel mixture. A 80% - 20% salt-gravel mixture is commonly used. The gravel, acts as an abrasive and gives motorists traction on what would otherwise be an icy surface.

a rusted car due to all the salt used during winter
A Rusted Car due to all the salt used during winter

Salt - Antifreeze for the Road

Salt trucks will dump five million tonnes of salt on Canadian roads during a typical winter.These roads salts act as a de-icing agent, and this creates safer road conditions.

The existence of icy roads will vary based on your geographical location within Canada. In Montreal, (where I live) temperatures drop below the freezing point for at least 5months of the year.

This chart details the number of days in a given month where the temperature is at, or below, the freezing point.

JanFeb Mar Apr May June JulyAug Sept Oct Nov Dec
30 27 27 13 10 0 0 0 8 2029

With all this cold weather, it's not surprising that we dump a lot of salt on our roads.In a typical winter, Montreal roads are coated with over 120,000 tonnes of road salt.

The scenario goes like this. It snows. The city spreads salt. Ice pellets mixed with freezing rain - more salt.

In addition to the 120,000 tonnes of road salt, 13.000 tonnes of sand or gravel are dumped on Montreal streets. That would explain the photo of the rust bucket on the top of this page.

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