Predict which of the following 0.1m solutions would have the lowest freezing point: Mg(Cl)2, catechin, or sucrose. Explain your reasoning.
The Correct Answer and Explanation is:
The 0.1 m MgCl₂ solution would have the lowest freezing point.
This prediction is based on the colligative property known as freezing point depression. A colligative property depends on the number of solute particles dissolved in a solvent, not on the identity or mass of those particles. When a solute is added to a solvent like water, it disrupts the formation of the solvent’s crystal lattice, which is necessary for freezing. This disruption requires a lower temperature to achieve freezing. Therefore, a higher concentration of dissolved particles leads to a greater depression of the freezing point and a lower final freezing temperature.
Let’s analyze each solution. Catechin and sucrose are both molecular compounds, meaning they are non-electrolytes. When they dissolve in water, they do not dissociate into smaller ions. Each molecule of sucrose or catechin remains as a single particle in the solution. Consequently, a 0.1 m solution of either sucrose or catechin will produce a total particle concentration of approximately 0.1 m.
In contrast, magnesium chloride (MgCl₂) is an ionic compound and a strong electrolyte. When it dissolves in water, it dissociates completely into its constituent ions. One formula unit of MgCl₂ breaks apart to form one magnesium ion (Mg²⁺) and two chloride ions (2Cl⁻). This means that for every one unit of MgCl₂ dissolved, three individual particles are released into the solution.
Therefore, a 0.1 m solution of MgCl₂ will have a total particle concentration that is ideally three times higher than that of the sucrose or catechin solutions. The effective particle concentration will be approximately 0.3 m (0.1 m Mg²⁺ + 0.2 m Cl⁻). Because the MgCl₂ solution contains the greatest number of solute particles, it will cause the most significant disruption to the freezing process, resulting in the largest freezing point depression and the lowest freezing point of the three options.thumb_upthumb_down
