Why does salt lower ice melting point?

Answer 1

I'll give two explanations. The first explanation needs an understanding of thermodynamics, the second one is easier.

The addition of salt to water results in an increase in "entropy".

This results in a lowering of the freezing point. That means the melting point is lower too. Unfortunately, you need to go through some mathematics to understand this explanation properly.

So, you may prefer this explanation:

When water freezes it forms ice (pure water). The water molecules still in the liquid phase have salt ions mixed in, reducing the concentration of water molecules. So, there's a reduction in water molecules going from liquid phase to the solid at the surface between liquid and ice. That means its harder to form ice and the melting point is lower.

The lower melting point is simply because the concentration of water molecules

in a salt solution is lower than in pure water. It's not because the salt "blocks"

the path of water molecules or affects the chemical bonds. In fact, many different substances can lower the melting point.