Chapter 2: Physical Properties of Solutions
Introduction
In this Chapter, we will discuss how the addition of solute to a pure solvent creates a solution whose physical properties are innately different than each of it's respective components. While we will review the intermolecular forces that allow for solvents to dissolve certain solutes, the physical properties we will discuss such as solution boiling and freezing point, vapor pressure, and osmotic pressure, are - interestingly - only dependent on the quantity of solute in solution rather than the i dentity of the solute at low concentrations. These physical properties of solutions that are sensitive to only the concentration of solute are called colligative properties.
Arctic fish represent an elegant interplay between biology and chemistry. Species like the variegated snailfish ( Liparis gibbus ), have evolved extraordinary adaptations to survive in the frigid waters of polar regions, where temperatures often drop below the freezing point of freshwater. Their secret lies in the biochemistry of colligative properties, specifically freezing point depression, a phenomenon where the presence of solutes lowers the temperature at which a liquid turns solid.Antifreeze proteins (AFPs) are specialized biomolecules produced by these fish to prevent ice crystal formation in their bodily fluids.
Figure 2.1: Some fish (left) have evolved to withstand subzero temperatures in arctic climes. Their main protection against the cold is the development of antifreeze proteins like Choristoneura fumiferana(right) whose presence in the blood disrupt the mechanical process of freezing on a molecular level. (CC BY 4.0; 2015, Kuiper et. al. via eLife - The Journal)
While their antifreeze adaptations enable them to thrive in extreme environments, these mechanisms are not unlimited. If temperatures drop too low, even AFPs and solutes cannot prevent freezing. Conversely, as global warming alters polar environments, these fish may face challenges if their adaptations become mismatched to their changing habitats.This fascinating use of colligative properties in nature not only demonstrates the survival strategies of arctic life but also serves as a reminder of the interconnectedness of chemistry and biology in shaping life on Earth.
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- 2.1: Types of Solutions and Solubility
- Solutions are homogeneous mixtures of two or more substances whose components are uniformly distributed on a microscopic scale. The component present in the greatest amount is the solvent, and the components present in lesser amounts are the solute(s). The formation of a solution from a solute and a solvent is a physical process, not a chemical one. Substances that are miscible, such as gases, form a single phase in all proportions when mixed. Substances that form separate phases are immiscible.
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- 2.3: Colligative Properties
- Colligative properties of a solution depend on only the total number of dissolved particles in solution, not on their chemical identity. Colligative properties include vapor pressure, boiling point, freezing point, and osmotic pressure. The addition of a nonvolatile solute (one without a measurable vapor pressure) decreases the vapor pressure of the solvent. The vapor pressure of the solution is proportional to the mole fraction of solvent in the solution, a relationship known as Raoult’s law.