# 25: Solutions II - Nonvolatile Solutes


• 25.1: Standard State of Nonvolatile Solutions
The standard state is a hypothetical solution of 1 mol/L in which the solute particles do not interact with each other.
• 25.2: The Activities of Nonvolatile Solutes
Electrolytic nonvolatile solutes have long-range ion-ion interactions, meaning they do not behave ideally even at low concentrations, and, unlike gases, liquids, and solids, there is not a simple substitution for the activity, $$a$$.
• 25.3: Colligative Properties Depend only on Number Density
Colligative properties are properties that depend on the number of particles rather than their total mass. This implies that these properties can be used to measure molar mass. Colligative properties include: melting point depression boiling point elevation osmotic pressure.
• 25.4: Osmotic Pressure can Determine Molecular Masses
Osmometry is still of some practical usefulness in polymer science as it is able to measure large molecules up to about 8000 daltons. Many polymers, however, are bigger than that and their mass distribution is usually determined by different means.
• 25.5: Electrolytes Solutions are Nonideal at Low Concentrations
A solution with a strong electrolyte produces multiple charged solutes in solution. We need to consider the dissociation process and stoichiometry of the salt, as well as the electrostatic interactions between the solutes. The result is that electrolytes behave nonideally even at low concentrations.
• 25.6: The Debye-Hückel Theory
Debye and Hückel came up with a theoretical expression that makes is possible to predict mean ionic activity coefficients as sufficiently dilute concentrations. The theory considers the vicinity of each ion as an atmosphere-like cloud of charges of opposite sign that cancels out the charge of the central ion.
• 25.7: Extending Debye-Hückel Theory to Higher Concentrations
The Debye–Hückel theory deviates from real systems at high concentrations because the model is simple and does not take into account effects such as ion association, incomplete dissociation, ion shape and size, polarizability of the ions, the role of the solvent. Several approaches have been proposed to extend the validity of the Debye–Hückel theory, including the Extended Debye-Hückel equation, the Davies equation, the Pitzer equations and specific ion interaction theory.
• 25.8: Homework Problems

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