Coligative References

Colligative Properties


As always I say: “Chemistry surprises you with the simplest things that you used to do in life”.


   Now, I am going to ask you: Have you ever seen people adding salt to ice in an ice cream maker? Have you ever traveled to countries where the snow is falling and in the next day people sprinkle salt on icy roads?
     The reason that people do this is not an alien behavior; they do because salt lowers the temperature at which water freezes. So, the question is how chemistry explains this? The temperature enough to make water harden into ice is 32 degrees Fahrenheit or 0 degrees Celsius. But when you sprinkle salt on ice, salt which is a compound called sodium chloride, interrupts the freezing process of the water. Some of the ice will melt because the salt pulls some water away from its crystal form (ice) and also mixes with the thin layer of water on top of the ice. This creates more saltwater, which will melt more ice. The dissolved salt will also prevent the melted ice (now water) from refreezing. Molecularly, salt slows the action of water molecules trying to join together into crystals to form ice or snow. Now, the temperature to form ice again is about -10°C.
     For example: on a winter road, the salt allows the ice to melt when the ambient temperature is below freezing. In other words, for the mixture of salt and ice or salt and water, it has to be colder than 0° C or 32° F to freeze. The depression of freezing point of water by salt is an example of the colligative properties of solutions.

The colligative properties are: freezing point depression, boiling point elevation, osmotic pressure and vapor pressure lowering. To understand how these properties work I am going to explain briefly the concept of solution.
     In general, a solution is a homogeneous mixture composed of a solute and solvent. The solute is the minority component which in this case is the salt and the solvent is the majority component which in this case is the water. The colligative properties depend on the number of particles (solute) that were dissolved in solution (that contain solvent). Basically, the more salt (solute) is added to the same amount of water (solvent), the lower its freezing point will be.


Let’s use chemistry in our favor to can go out in winter without the snow covering us at all.


I want to know others chemistry tricks that you use to combat the snow?
Let me know which are yours and remember see the video and photo below. Also, if you want to read more about colligative properties go to the references.


Thanks,

-Stephanie

References

1) https://www.highlightskids.com/science-questions/how-does-salt-melt-ice-and-snow

2) Tro, N. J.; “Chemistry: A Molecular Approach”, 3rd ed., Pearson Prentice Hall: New Jersey, 2014.