So THAT's Why Salt Gets Rid Of Ice

Parts of the UK are still facing yellow snow and ice warnings, which began last week. 

That means Scotland’s hilariously named gritters are out and about, and roads around the rest of Britain and Northern Ireland are similarly being salted.

I have a huge yellow grit container outside my flat which we’ve been sprinkling into the block’s parking lot for days now. Grit is usually rock salt ― but why does sodium get rid of ice to begin with?

After all, it’s not like it’s any warmer than the other ingredients in your cupboard.

Salt doesn’t technically ‘melt’ ice, but it does help water to do so

Encyclopedia Brittanica’s site says that the ice on your road isn’t usually completely solid as there’s often a thin layer of water on top.

The temperature would have to be very, very cold for it to be completely solid. 

Those water and ice layers are constantly interacting. The water melts the ice, the ice freezes the water back, and so on.

Ice wins more battles when it’s colder; but as it warms up, water becomes the victor. 

So where does salt come into this battle? Well, the Local Government Association says rock salt lowers the freezing temperature of the water, meaning it no longer becomes solid at 0°C. 

The ions in salt break apart in water, making it harder for H2O molecules to stick together (as is needed to form ice).

Some councils use calcium chloride rather than sodium chloride (table salt) to treat roads, which has three ions instead of cooking salt’s two, making it even more effective at breaking up ice. 

The less easy it is for ice to freeze the water back into a solid state, the sooner it’ll melt. 

Additionally, more water helps to melt more ice; it’s a surprisingly sophisticated double-pronged attack. 

Can it be too cold for salt to melt ice?

If all salt does is make water freeze at a lower temperature, wouldn’t reaching that level of chill keep ice intact?

Well, yes, the Local Government Association says. 

“Salt will work at temperatures down to minus 8-10°C,” it says. “Below that temperature, salted roads will still freeze.” 

Temperatures could hit -16°C in parts of Scotland today, for reference.

And the salt doesn’t do all that melting magic by itself either ― traffic helps to crush and spread the grit across the road.

That helps to break the ice down further and means more areas of the pathway are covered in salt, which is why the first drivers on a road are usually the ones most likely to slip.

The more you know, eh...