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Which of the Following Aqueous Solutions Has the Lowest Freezing Point?
Introduction:
When a solute is dissolved in a solvent, it affects the properties of the resulting solution. One such property is the freezing point. The freezing point of a solution is the temperature at which it changes from a liquid to a solid state. The presence of a solute in the solvent lowers the freezing point, a phenomenon known as freezing point depression. In this article, we will explore which of the following aqueous solutions has the lowest freezing point and explain the concept of freezing point depression in detail.
Aqueous Solutions and Freezing Point Depression:
An aqueous solution is a solution in which water is the solvent. When a solute is dissolved in water, it dissociates into its constituent ions. The presence of these ions affects the freezing point of the solution. According to Raoult’s Law, the lowering of the freezing point is directly proportional to the molality of the solute. Molality is defined as the moles of solute per kilogram of solvent.
To determine which of the following aqueous solutions has the lowest freezing point, we need to consider the nature of the solute and its concentration. The following solutions will be examined:
1. Sodium chloride (NaCl) solution
2. Sucrose (C12H22O11) solution
3. Ethanol (C2H5OH) solution
Factors Affecting Freezing Point Depression:
The freezing point depression depends on several factors. Firstly, the nature of the solute plays a significant role. In general, ionic solutes like NaCl dissociate completely into ions when dissolved in water, resulting in a greater decrease in freezing point compared to non-ionic solutes like sucrose.
Secondly, the concentration of the solute influences the freezing point depression. Higher concentrations of solute result in a larger decrease in the freezing point. This is because more solute particles are available to disrupt the formation of solid crystals.
Lastly, the Van’t Hoff factor, denoted by “i,” also affects the freezing point depression. The Van’t Hoff factor represents the number of particles formed in a solution from one solute molecule. For example, NaCl dissociates into two ions (Na+ and Cl-) in water, so its Van’t Hoff factor is 2. Sucrose, being a non-ionic solute, does not dissociate, so its Van’t Hoff factor is 1.
Analysis of Aqueous Solutions:
1. Sodium chloride (NaCl) solution:
NaCl dissociates into Na+ and Cl- ions in water. This ionic nature of NaCl results in a high degree of freezing point depression. Additionally, NaCl is a highly soluble salt, meaning it can reach high concentrations in water. Therefore, a sodium chloride solution would have the lowest freezing point among the given options.
2. Sucrose (C12H22O11) solution:
Sucrose does not dissociate into ions in water. Therefore, it does not have as significant an effect on the freezing point depression as an ionic solute. However, sucrose is a polar molecule and can form hydrogen bonds with water molecules, which can still lower the freezing point to some extent.
3. Ethanol (C2H5OH) solution:
Ethanol is a non-ionic solute and does not dissociate in water. However, it is miscible with water, meaning it forms a homogeneous mixture with water. Ethanol molecules can also form hydrogen bonds with water molecules, leading to some freezing point depression. However, its effect would be less compared to ionic solutes.
FAQs:
1. How does freezing point depression occur?
Freezing point depression occurs due to the presence of a solute in a solvent. The solute particles disrupt the formation of solid crystals by occupying the spaces between solvent molecules, resulting in a lower freezing point.
2. Can the concentration of the solute affect freezing point depression?
Yes, the concentration of the solute directly affects freezing point depression. Higher concentrations of solute lead to greater freezing point depression.
3. Why do ionic solutes have a larger effect on freezing point depression compared to non-ionic solutes?
Ionic solutes dissociate into ions in water, resulting in more solute particles present in the solution. These ions disrupt the formation of solid crystals more effectively, leading to a larger decrease in the freezing point compared to non-ionic solutes.
4. What is the Van’t Hoff factor, and how does it affect freezing point depression?
The Van’t Hoff factor represents the number of particles formed in a solution from one solute molecule. It affects freezing point depression as more particles in a solution result in a larger decrease in the freezing point.
Conclusion:
In summary, the presence of a solute in an aqueous solution lowers its freezing point, a phenomenon known as freezing point depression. Among the given options, a sodium chloride solution would have the lowest freezing point due to its ionic nature and high solubility. Sucrose and ethanol solutions, being non-ionic solutes, would still cause some freezing point depression, but to a lesser extent. Understanding the factors affecting freezing point depression can help predict the behavior of different solutions and their freezing points.
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