When a nonchemist thinks of salt, NaCl (sodium chloride) comes instantly to mind, but for a chemist, many other compounds also fit the bill, and CaCl2 is one of them. The CaCl2 compound name is calcium chloride. Like table salt, it's a white crystal at room temperature, but it has properties that clearly set it apart.
Calcium chloride can be obtained by refining soda ash, natural brine or limestone. It dissolves readily in water and will actually turn to liquid if left long enough in a humid environment. Common uses include deicing roads, accelerating the set time of concrete, controlling humidity and improving the taste of beer.
CaCl2 Common Uses on Roads and Highways
Like sodium chloride, calcium chloride lowers the melting point of ice, so one of its most common uses is for road deicing. It works at much lower temperatures — minus 20°F vs. 20°F for rock salt — because it actually releases heat in an exothermic reaction when it dissolves. It costs more per pound than rock salt, but you need less of it to do the same amount of deicing. Deicing products often contain both sodium chloride and calcium chloride.
Calcium chloride is hygroscopic, which means it attracts moisture from its environment. This quality makes it a good chemical to use for suppressing dust on gravel roads and other byways.
Calcium Chloride for Humidity Control
CaCl2 is more than just hygroscopic; it is deliquescent, which means it can absorb enough moisture to turn to liquid brine at room temperature. It's the most common ingredient in moisture absorbers available at big box stores for controlling humidity in drawers and closets. You often find it combined with baking soda, which is a deodorizer.
Dehumidifying with calcium chloride is not without its hazards. CaCl2 is corrosive and promotes rust, so it should not be used around metals. Moreover, prolonged exposure can cause respiratory issues and lung damage. Silica gel is a safer desiccant and is often used instead of calcium chloride.
Applications in the Food Industry
Calcium chloride is safe to consume and is a common food additive. It adds firmness to cheese, tofu and canned fruits and vegetables, and it provides a way to enhance the salty taste of pickles without adding extra sodium. Brewers add it to the water they use to make beer to lower the pH and add alkalinity, which improves the taste.
Calcium chloride is a common ingredient in sports drinks. When it dissolves in water, it splits into positive calcium ions and negative chlorine ones, and because the calcium chloride formula includes two chloride ions, it creates a more powerful electrolyte than sodium chloride, which has only one.
The ability of CaCl2 to completely dissociate into its component ions gives the compound a salty taste, and it could be a substitute for table salt were it not so hygroscopic. However, its propensity to absorb water causes intestinal problems and abdominal pain if you ingest it in large amounts.
Using Calcium Chloride in Construction
Because calcium chloride absorbs water so well, and it generates heat when doing so, cement workers add it to concrete to accelerate the cure rate at low temperatures. The addition of a 2 percent concentration creates the same cure rate at 50°F as plain concrete has at 70°F.
Kits for testing the moisture content of concrete slabs typically contain calcium chloride in a container. Because CaCl2 absorbs off-gassing water vapor from the slab, the test consists of weighing the container, leaving it on the slab for a prescribed period, weighing it again and recording the gain in weight.