The key difference between rock salt and calcium chloride is that as de-icing agents, calcium chloride is highly effective at lower temperatures than the effectiveness of rock salt at the same low temperature.
Both rock salt and calcium chloride are important mainly as de-icing agents. However, their effectiveness depends on the temperature at which we use it as the de-icing agent. Calcium chloride can prevent the formation of ice from water at very low temperatures, around −52 °C. But rock salt works better around 0 °C.
CONTENTS
1. Overview and Key Difference
2. What is Rock Salt
3. What is Calcium Chloride
4. Side by Side Comparison – Rock Salt vs Calcium Chloride in Tabular Form
5. Summary
What is Rock Salt?
Rock salt is a natural mineral that contains sodium chloride. Therefore, the chemical formula is NaCl. The mineralogical name of this mineral is halite. Rock salt is the common name. Typically, this mineral is colourless or white. But, sometimes, it may have a colour such as light blue, dark blue, purple, pink, red, orange, yellow or grey. Because, it is due to the presence of impurities along with sodium chloride.
Since the chemical formula of the repeating unit of halite is NaCl, the formula mass is 58.43 g/mol. It has a cubic crystal structure. The mineral is brittle, and the mineral streak is white. When considering the occurrence of this mineral, it exists in vast beds of sedimentary evaporites. These evaporites create due to drying of lakes, seas, etc.
Figure 01: Pink coloured Halite
The most important use of this salt is managing ice. Brine is a solution of water and salt. Since brine has a lower freezing point compared to pure water, we can put brine or the rock salt on ice (at 0 °C). This will cause the ice to melt. Hence, in cold climates, people use this salt to spread in their sidewalks and driveways to melt the ice.
What is Calcium Chloride?
Calcium chloride is an inorganic compound and a salt having the chemical formula CaCl2. It is colourless and crystalline that occurs in a solid state at room temperature. It mainly exists as a hydrated salt rather than the individual compound. Hence the precise chemical formula is CaCl2(H2O)x. Here, x can be 0, 1, 2, 4, or 6. This salt is hygroscopic. Thus, we can use it as a desiccant.
Figure 02: Calcium Chloride Appearance
The molar mass of the compound is 110.98 g/mol. It has an orthorhombic crystal structure in its anhydrous form and trigonal crystal structure in its hexahydrate form. When considering the occurrence of this compound, it rarely occurs in nature as the mineral sinjarite (dihydrate form) or antarcticite (hexahydrate form). Typically, for almost all the uses of this compound, we produce it from limestone. This forms as a byproduct of the Solvay process. Or else, we can obtain it from the purification of brine.
Here too, the major application of this compound is in de-icing. It can prevent ice formation by depressing the freezing point of water. Above all, this compound is much more effective at lower temperatures as a de-icing agent.
What is the Difference Between Rock Salt and Calcium Chloride?
Rock salt is a natural mineral that contains sodium chloride whereas calcium chloride is an inorganic compound and a salt having the chemical formula CaCl2. Chemically, this is difference between rock salt and calcium chloride. Since these two materials have a different chemical composition, the molar mass is different from each other as well: the formula mass of rock salt is 58.43 g/mol while the molar mass of calcium chloride is 110.98 g/mol. Hence, based on properties, this is a significant difference between rock salt and calcium chloride.
When considering the applications, both these compounds are important mainly in managing ice. Hence, the key difference between rock salt and calcium chloride is that, as de-icing agents, calcium chloride is highly effective at lower temperatures than the effectiveness of rock salt at the same low temperature.
The infographic below gives more details on the difference between rock salt and calcium chloride.
Summary – Rock Salt vs Calcium Chloride
Both rock salt and calcium chloride are important in managing ice formation. Yet their effectiveness differs from each other depending on the temperature. Therefore, the key difference between rock salt and calcium chloride is that as de-icing agents, calcium chloride is highly effective at lower temperatures than the effectiveness of rock salt at the same low temperature.
Reference:
1. “Halite.” Wikipedia, Wikimedia Foundation, 17 Oct. 2018. Available here
2. “Calcium Chloride.” Wikipedia, Wikimedia Foundation, 1 Oct. 2018. Available here
Image Courtesy:
1.”Halite-Nahcolite-60710″By Rob Lavinsky, (CC BY-SA 3.0) via Commons Wikimedia
2.”Calcium chloride CaCl2″By No machine-readable author provided. (CC BY-SA 3.0) via Commons Wikimedia