If cost per gram were not a concern, which of the following substances would be the most efficient per unit mass for melting snow from sidewalks and roads: glucose 1C6H12O62, LiCl, NaCl, or CaCl2? Explain.

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Identify the property of the substances that affects their efficiency in melting snow. This property is the 'freezing point depression' which is the ability of a substance to lower the freezing point of water when dissolved in it.

Understand that the effectiveness of a substance in melting snow is determined by the number of particles it releases into solution per unit mass. More particles result in a greater freezing point depression.

Analyze the substances given: glucose (C6H12O6) is a molecular compound that does not dissociate into ions in solution, thus contributing fewer particles per mole compared to ionic compounds.

Consider the ionic compounds: LiCl, NaCl, and CaCl2. These dissociate into ions when dissolved in water. LiCl dissociates into 2 ions per formula unit, NaCl also dissociates into 2 ions, but CaCl2 dissociates into 3 ions (1 Ca2+ and 2 Cl-).

Conclude that CaCl2 would be the most efficient per unit mass for melting snow, as it provides the highest number of particles per unit mass, leading to a greater freezing point depression compared to the other substances.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Colligative Properties

Colligative properties are properties of solutions that depend on the number of solute particles in a given amount of solvent, rather than the identity of the solute. These properties include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure. In the context of melting snow, the ability of a substance to lower the freezing point of water is crucial, as it determines how effectively the substance can melt ice.

Dissociation of Ionic Compounds

Ionic compounds, when dissolved in water, dissociate into their constituent ions. The extent of this dissociation affects the number of particles in solution, which in turn influences the colligative properties. For example, sodium chloride (NaCl) dissociates into two ions (Na+ and Cl-), while calcium chloride (CaCl2) dissociates into three ions (Ca2+ and 2Cl-), making it more effective at lowering the freezing point of water compared to NaCl.

Freezing Point Depression

Freezing point depression is a colligative property that describes the decrease in the freezing point of a solvent when a solute is added. The formula for calculating freezing point depression is ΔTf = i * Kf * m, where 'i' is the van 't Hoff factor (number of particles the solute dissociates into), 'Kf' is the freezing point depression constant, and 'm' is the molality of the solution. Substances that dissociate into more particles will have a greater effect on lowering the freezing point, making them more efficient for melting snow.