Winter is a fact of life and with it comes many considerations like "What shovel should I buy?" and "How long can I wait to put up Christmas lights?" Today though, I would like to address the other two considerations that nag us every year:
1. What sidewalk salt should I use?
2. What antifreeze should I use?
What's it made of?
Salts: So, we throw around the word "salt" a lot. Sea salt, table salt, salt of the earth, but really there are many types of salts. Salt is a word that describes an ionic compound. Now, this in itself may be another term, but ionic compound just stands for a thing that is made up of parts with charges. These can be atoms or molecules themselves. One of the parts has extra electrons and is negatively charged. This is the anion. The other is missing some electrons and is positively charged. This is called a cation.I have made a diagram to help YUMMY:
The key thing about a salt is that when put in water it will dissociate or separate into the two charged parts. Here is another description using dogs to demonstrate (super cute).
Table salt is made of sodium (Na) and chloride (Cl), but that is one of many salts. The salt used by the DOT is typically calcium chloride CaCl2. Since calcium has two positive charges it needs two negatively charged chloride ions to be neutral. Sea salt is just salts from the ocean. It has all kinds of cations and anions in it. Sometimes magnesium (Mg) as a cation and sometimes bromine (Br) as anions. A great deal of it is still sodium chloride, but it is not as pure as the table salt in your shaker.
Antifreeze: Now we will discuss why salt stops water from freezing or melts ice in a bit, but the term antifreeze has little to do with the process that the salts are doing. Antifreeze is really just a different molecule altogether that can be used to prevent water from freezing, but often is just used by itself to be a liquid that will not freeze at low temperature. The molecules most often employed are ethylene glycol and propylene glycol. Glycol is a term for molecules that have neighboring alcohol groups on them otherwise known as 1,2-diols (see below). The presence of these groups on small molecules (ethylene and propylene) mean that the freezing point is very low and the substance can dissolve in water very well.
How does it work?
Salt: Salts work to break up ice or prevent water from freezing by a process called Freezing Point Depression. That seems like a logical name. In essence, each ion dissolved in water helps to disrupt the ability of the water to freeze at its normal temperature. The more ions, the lower the freezing point. One sodium chloride provides two ions, a whole handful of sodium chloride provides many ions, and water no longer freezes at 32 degrees F, but rather closer to -6 degrees F (0 C -> -20 C). Calcium chloride, if you remember, has three ions and does an even better job. Here is a link to a bunch of other possible salts and their properties. One fun trick with kids is to make an ice cube stick to a string, or my favorite, Homemade Ice Cream!Antifreeze: The not-freezing ability of antifreeze is mostly due to its interactions between molecules. It is not water, so has fewer interactions and therefore takes longer to freeze. Pure ethylene glycol freezes at about 9 degrees F and propylene glycol at -54 degrees F. Both are lower than water, and therefore keep flowing even in relatively cold weather. (I should also note here that they boil at 387 F and 370 F respectively, way higher than water. Maybe I will revisit this next summer.)
So, Which should I Use?
Salt: Here's where it depends. You just need more ions, so technically you can pick any salt. You may need more sodium chloride than calcium chloride since there are fewer ions, but it also costs less. There are also "pet friendly" salts that use amine salts, but again, these are more expensive and often less effective because their ions are bigger and bigger. A 6.5 pound bottle of pet-friendly salt is about the same cost as a 20 pound bag of a "chloride" salt. Though typically prevent paws from drying and cracking, you could also just wipe down paws. The ASPCA has some tips.The one thing you might want to consider is vegetation and concrete. Some salts can take a toll on both. Here is a link that describes some considerations. Bigger ions are typically better, so Magnesium or Calcium chlorides are a little less corrosive to the driveway.
Antifreeze:
Well, both work relatively well. Most often you mix them with water, but the key factor to take into consideration is whether you have pets and kids around that might get into the pure antifreeze if unattended. Though both can be toxic, ethylene glycol should be avoided if you are not attentive to your children or pets. Ethylene glycol can be more dangerous to animals and kids because it has the added problem of tasting semi-sweet. Dogs that get into a pool of it have a tendency to drink it all up, exposing themselves to a larger dose. Propylene glycol is the safer alternative. As it turns out, that one extra carbon changes the biochemical pathway for degradation. Ethylene glycol is processed by the body to glyoxylic acid and oxalic acid, both of which can harm the kidneys and other organs.
Instead of making a molecule called oxalic acid, propylene glycol degrades into lactic acid and pyruvic acid. These two molecules are part of normal metabolism. As a result, unless consumed in really high doses, propylene glycol is only mildly toxic. Combining this with its good antifreeze properties, I think it might be a better choice for the money. Because of this lower toxicity, it is also a main component of aircraft deicers and is in the electronic cigarettes that help people quit smoking. Sometimes when deicing you might smell a sickly sweet smell in the cabin, that is a bit of the proplyene glycol getting pulled into the air handler. Nothing to worry about!
