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Explain whether sodium chloride or calcium chloride would be a more effective substance to melt...

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Explain whether sodium chloride or calcium chloride would be a more effective substance to melt the ice on a slick sidewalk.

Colligative Properties of Electrolyte Solutions:

One of the colligative properties is freezing-point depression, which states that the addition of solute lowers the freezing point of the solution relative to the freezing point of the pure solvent. For electrolyte solutes, the freezing-point depression {eq}ΔT_f{/eq} is given by:

{eq}ΔT_f = -iK_fm{/eq}, where:

  • {eq}K_f{/eq} is the cryoscopic constant, a property of the solvent
  • {eq}m{/eq} is the molality of solute (moles solute per kg solvent)
  • {eq}i{/eq} is the van't Hoff factor, a correction factor for electrolytes equal to the amount of ions dissolved per formula unit of solute.

For a general strong electrolyte {eq}M_aX_b{/eq}, the dissociation reaction in water (assuming 100% dissociation) is:

{eq}M_aX_b → aM^{b+} + bX^{a-}{/eq}

Because 1 mole of the solute yields {eq}a + b{/eq} moles of ions, the van't Hoff factor is {eq}i = a+ b{/eq}.

Answer and Explanation: 1

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Assume that {eq}NaCl{/eq} and {eq}CaCl_2{/eq} are both strong electrolytes that dissociate completely into ions in solution:

{eq}\begin{align*} NaCl...

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Colligative Properties and Raoult's Law

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Chapter 8 / Lesson 7
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Learn about colligative properties and their equations. See Raoult's law in vapor pressure, a colligative property, and osmotic pressure problem examples. Learn about freezing point depression and boiling point elevation.


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