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Name: Kiya
Status: student
Grade: 9-12
Country: Canada
Date: Winter 2009-2010

Why are airplane de-icers soluble in water?

Hi Kiya,

The short answer to your question is that any deicer has to be soluble in water to work. In a way, your question is rather like asking if it is possible to make coffee, if the coffee did not dissolve in water!

When a deicer such as ethylene glycol is sprayed on ice, the ice begins to "dissolve" into the deicer. As more and more ice dissolves in the deicer, the volume of the deicer-water mixture become larger, thus there is more and more liquid water and deicer mixture, and the dissolving of the remaining ice goes progressively faster. It is important to understand that the liquid mixture of water (from melted ice) and deicer, cannot freeze any more because the deicer dissolved or mixed with the water lowers the freezing point of the mixture (just as adding antifreeze to the water in a car's cooling system, lowers its freezing point, and keeps the mixture from freezing).

If deicer did not dissolve in water, none of the above would work. The deicer would just sit there and not interact with either ice or water. Any water that somehow was still liquid, would be just pure water (since the deicer would not mix with it), and would instantly freeze.

Bob Wilson

In order to "de-ice" the de-icer must be soluble in water. Otherwise it could not affect the equilibrium temperature of the solid water ice and the liquid water. To a first approximation, it is the number of particles (ions and/or non-ionic particles) that dissolves in the water that changes the efficiency of the de-icer. This is why de-icers tend to be mixtures of ionic compounds -- for example, Ca(Cl)2 + urea CO(NH2)2. The former produces three ions per mol; the latter produces only one particle per mol, but is very water soluble. This is a bit over-simplified because corrosion, and other factors must also be taken into account.

Vince Calder

Hi Kiya,

Aircraft deicers work on the same principle as the salt we put on our roads or walkways during winter or the antifreeze we put in car radiators. They salt used on roads is usually NaCl, CaCl2, or MgCl2. They work by slowly dissolving into the snow and ice and the combination of the heat of solution and freezing point depression helps melt the snow and keep it from refreezing. The antifreeze in cars is usually ethylene glycol and it works by lowering the freezing point of water so that it will remain liquid at lower temperatures. Aircraft deicers are usually formulations that include ethylene glycol or propylene glycol. Chloride salts are not allowed because they can speed up the corrosion of metals. In order for the deicer to work, it must dissolve into any water that is formed or present and lower the temperature of freezing for that solution - preventing it from forming ice once it has become a liquid solution. So, in answer to your question, the deicer must first dissolve into water before it can act to lower the freezing point and prevent ice reformation.

Look up "colligative properties" and "freezing point depression" in this site if you want to know more about the principles behind the lowering of the freezing point.

Greg (Roberto Gregorius)
Canisius College

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