You may or may not have witnessed this on certain social media platforms, like Facebook or YouTube. Basically, this challenge requires 3 things: ice, salt and skin. The contestant pours some salt on the skin(most preferably the palm), puts the ice on top of the salt and then adds pressure, making sure little water is lost. The challenge is to withstand this for as long as possible
What really happens there?
To understand what happens in that, we need to talk just a little bit about water and watery solutions.
Water has a freezing point of 0 degrees centigrade, or 32 degrees Fahrenheit. From that moment on, water will solidify, turning into ice. The cooler the temperature, the faster the process.
Well, that happens when water is ‘pure’, that is, without any contaminants. When you add plain old table salt, things change. Salty water has a lower freezing point. That means that it will freeze below 0 degrees C (32 degrees F) .
But in order to obtain a watery solution of salt, salt must firstly dissolve in water. And this process requires energy in the form of heat. This is called an endergonic process. Typically, it could get it from the surrounding air. But, conveniently enough, someone left their palm there. So it will absorb the heat from there.
What does it lead to?
The net effect is that heat is being transferred from the skin to the solution. From the skin’s point of view, this is a net loss. Greater that it could replenish. So, believe it or not, this will lead to early-stage frostbite. And although many of the participants experience what may feel like a burning sensation, this actually comes from an inability of the brain to discern between very hot stimuli and very cold stimuli.
Although it may seem fun to see someone ‘scorch’ their hand, this experiment should not be performed unless it has to prove a purpose. And the purpose is the demonstration of basic physics, not fun.
Salt ice challenge
Confusing hot and cold