I know this question has been asked several times, but I have an additional question.
In the following link you (or a colleague) say that CaCl2, due to its 3 ions in solution, causes a low melting temperature. question 7454
If, for example, AlCl3 were to be used as road salt, then one would have 4 ions in solution. Does this mean that the melting temperature goes even lower?
Would it also be possible to use ternary salts, such as Fe2(SO4)3. This then has 5 ions => even lower melting temperature!!
Am I right, or am I getting my conclusions wrong?
Answer
You are 100% correct in your reasoning, the freezing point depression is a function of the number of particles you put into solution. The charge of the ions is also important, so CaCO3 is better than NaCl, but poorly soluble. Other arguments, such as that of the energy released during dissolution, are of minor importance, although they are of course interesting with regard to the kinetics of the event.
In terms of toxicity, CaCl2 is OK, because the Ca counteracts acidification, the Cl anion is rather neutral, and one of the less harmful anions, nitrate and sulfate, are less interesting.
An additional reason is of course the financial aspect. CaCl2 is an important by-product of the chemical industry, and it is interesting for a company like Solvay to valorise part of that product as road salt instead of having to have expensive processing carried out. Evil tongues claim that Solvay’s good connections with the government are the reason that road salt is used so lavishly in Belgium, and that much more is used than is actually necessary.
I hope this answers your question satisfactorily.
Koen Parmentier
Answered by
dr. Koen Parmentier
Chemical pollution of the marine environment Freshness parameters for marine fishery products Biochemical indicators of pollution Genetic authenticity and relationship analysis
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