"De-icing salt" is used to melt snow and ice on streets. The highway department of a small town is deciding whether to by NaCl or CaCl2 for the job. The town can obtain NaCl for $0.25/kg. What is the maximum the town should pay for CaCl2 to be cost effective?
2006-09-04 15:45:31 · 5 answers · asked by buttrefly007 1 in Science & Mathematics ➔ Chemistry
You need to know the specific heat of formation for salt and calcium chloride to compare them as this is the heat energy that they give off to melt the ice.
Once source lists Calcium Chloride at -1309 kJ /mol
I found numbers for salt at about -609 Kj /mol
The molecular weight for NaCl is 54.4 g, CaCl2(6H20) is 219.1 g
So a kg of salt provides 11,195 Kj, and a kg of CaCl2 4,668 Kj.
If my numbers are correct (you better check) You should not pay more than $0.104/kg for CaCL2.
2006-09-04 16:19:08 · answer #1 · answered by Computer Guy 7 · 0⤊ 0⤋
They are both salts. The maximum for the town to pay is $.38/kg.
The way de-icing salt works it that the salt breaks into its ions when it hits the water (the ice in this case). These ions break down the bonds in the ice and thus melt it. So...with NaCl, you get two ions, but with CaCl2, you get three ions. So one kg of CaCl2 does more than on kg of NaCl. So divide $0.25 by 2 to get the price per ion, which is $.125, and then multiply that by 3 to get what the price of CaCl2 should be since it has three ions.
2006-09-04 15:58:24 · answer #2 · answered by Anonymous · 1⤊ 0⤋
This problem relates to colligative properties. (see source)
The salt act as a substance that lowers the freezing point. If the freezing point is lower then the substance may not be cold enough to freeze.
Each formula unit of NaCl produces two particles in solution, one sodium ion and one chloride ion.
However each formula unit of CaCl2 produces three particles, one calcium ion and two chloride ions.
If the highway department buys Calcium chloride at the same price as sodium chloride, then they are getting one third extra ions for the same price.
If they have to pay more then $0.38 / kg then they will be paying more then they should.
so they should try to buy the calcium chloride for less than $0.38 / kg
2006-09-04 16:24:37 · answer #3 · answered by Roy G. Biv 3 · 0⤊ 0⤋
Hi. If the efficacy of calcium chloride is the same as sodium chloride the answer is %0.25 per Kilogram. But Andrew B's answer, assuming it's correct (and I do) points to a different answer.
2006-09-04 15:59:31 · answer #4 · answered by Cirric 7 · 0⤊ 0⤋
nothing use only salt
2006-09-04 15:47:28 · answer #5 · answered by rav 4 · 0⤊ 0⤋