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

## Question:

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}.