Question

Common salt (NaCl) is spread on roads to prevent ice formation. The cost of the salt is $1.92 for 10 kg. A rich new source of CaCl2 was discovered and mined at $1.49 for 10 kg. Which salt is more cost-effective?

Answer 1

The salt lowers the freezing point of water , so that ice is unable to form.

The depression in freezing point is given as :

Delta Tf = i.kf.m

where i is vant hoffs factor , 2 for NaCl and 3 for CaCl2

m is the molality

molar massd of NaCl is 58.44 g/mol whereas that of CaCl2 is 111 g/mol

This means almost double number of moles of NaCl are present in 10 kg amount than that of CaCl2.

Since number of moles are double , its molality in fixed amount of water will be more, and so will be its freezing point depression by 10 kg salt , as compared to CaCl2.

So I believe NaCl salt is more cost effective.