Why does ice melt?

During bad winters in the UK, we use nearly 2 million tonnes of salt to melt snow and ice. But how does salt melt ice?

Salt melts ice due to a process called freezing point depression. When a substance dissolves in water, it lowers the freezing point of the water. In other words, it requires lower temperatures for the water to freeze.

Pure water freezes at 0 degrees Celsius. When we add salt to the water, it dissociates into its ions. These ions disrupt the crystal structure of the ice, making it more difficult for the ice molecules to arrange themselves into a solid lattice and thus lowering the freezing point of the water.

As a result, the presence of salt in water causes the freezing point to drop below 0 degrees Celsius; This means that the ice will not remain solid at temperatures below 0 degrees Celsius when salt is present. Instead, the ice will start to melt, forming a brine solution of saltwater.

The process of using salt to melt ice is commonly used to de-ice roads and sidewalks during winter. The salt lowers the freezing point of the water on the surface, preventing it from solidifying into ice and helping to melt existing ice and snow.

Watch our video below, join Wilf Wonders as he explains the science behind melting ice and learn new fun facts that you can share with family and friends this Christmas!

Oh ho ho, and please do share your science highlights with us @IETeducation! #SantaLovesSTEM.