Should the Town Buy NaCl or CaCl2 for De-icing?”

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Discussion Overview

The discussion revolves around the decision of a town's highway department regarding the purchase of de-icing salt, specifically comparing the cost-effectiveness of sodium chloride (NaCl) versus calcium chloride (CaCl2). The focus includes calculations related to moles and molar mass, as well as the implications of the chemical properties of each compound for de-icing effectiveness.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant inquires about the maximum price the town should pay for CaCl2 to remain cost-effective compared to NaCl.
  • Another participant emphasizes the importance of understanding moles and molar mass in solving the problem.
  • A participant expresses uncertainty about the chemistry involved and requests assistance.
  • One participant calculates the number of moles in 1 kg of NaCl and CaCl2, reporting 0.05844 mol for NaCl and 0.11098 mol for CaCl2, seeking confirmation of their calculations.
  • A later reply corrects the molar mass values and provides a detailed breakdown of the moles produced by each compound, suggesting two different ratios for cost comparison based on the de-icing effect of chloride ions.
  • Concerns are raised about the practical implications of using CaCl2 due to its hygroscopic nature, although this is noted as potentially outside the scope of the introductory chemistry question.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and confidence in their calculations, with some providing corrections and alternative interpretations of the problem. There is no consensus on the maximum price for CaCl2 or the best approach to the problem, indicating ongoing disagreement and uncertainty.

Contextual Notes

Participants highlight the need for clarity on whether to consider the de-icing effect of the chloride ions in their calculations. The discussion also reflects uncertainty regarding the practical implications of using CaCl2 due to its hygroscopic properties.

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Homework Statement




"De-icing salt" is used to melt snow and ice on streets. the highway department of a small town is decideing whether to by NaCl or CaCl2 for the job. The town can obtain NaCl for $0.36/kg. What is the maximum the town should pay for CaCl2 to be cost effective? in kg



Homework Equations





The Attempt at a Solution




I am sure this is very simple but I am not sure what to do with it...
 
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Do you know about moles and molar mass of compounds?
Do you know how to work out how much NaCl there is in a kg?

You have posted 3 questions which are basically the same thing - they all need this step.
 
I am really not sure...i am pretty new to chemistry and not very good at it, can i get some help
 
Can you work out how many moles are in 1 kg of NaCl and CaCl2? What part are you confused on?
 
i worked out .05844 mol in 1 kg for NaCL
and .11098 mol in 1 kg of CaCl2

is this correct
 
No, molar mass of NaCl is 58.4g, CaCl2 is 111g
but for every mole of CaCl2 you get twice as much Cl as you do from NaCl

So 1kg of NaCl gets you 17.12moles of Na and Cl, 1kg of CaCl2 is 9.0 moles of Ca and 18.0moles of Cl

It isn't clear from the question if you supposed to take into account the de-icing effect of the Cl ion so the answer is either.
That you should pay 9/17.2 = 0.52 times as much for CaCl2
or if you are only concerned about Cl then you should pay 18/17.2 = 1.05 times as much for CaCl2


(Actually it's a very stupid example because CaCl2 is so hydroscopic it will almost certainly not be 111g/mole - but since this is an intro chemistry question you can ignore this)
 
Last edited:

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