Chemistry Textbook
- 1. Matter and MeasurementsToggle Dropdown
- 2. Atoms, Molecules and IonsToggle Dropdown
- 3. Composition of Substances and SolutionsToggle Dropdown
- 4. Stoichiometry of Chemical ReactionsToggle Dropdown
- 5. ThermochemistryToggle Dropdown
- 6. GasesToggle Dropdown
- 7. Chemical Bonding and Molecular GeometryToggle Dropdown
- 8. Liquids, Solids, and Modern MaterialsToggle Dropdown
- 9. Solutions and Colligative Properties
- 10. KineticsToggle Dropdown
- 11. Chemical Equilibria and ApplicationsToggle Dropdown
- 12. ThermodynamicsToggle Dropdown
- 13. ElectrochemistryToggle Dropdown
- 14. AppendicesToggle Dropdown
- Appendix A: Periodic Table of Elements
- Appendix B: Essential Mathematics
- Appendix C: Units and Conversion Factors
- Appendix D: Fundamental Physical Constants
- Appendix E: Water Properties
- Appendix F: Composition of Commercial Acids and Bases
- Appendix G: Standard Thermodynamic Properties for Selected Substances
- Appendix H: Ionization Constants of Weak Acids
- Appendix I: Ionization Constants of Weak Bases
- Appendix J: Solubility Products
- Appendix K: Formation Constants for Complex Ions
- Appendix L: Standard Electrode (Half-Cell) Potentials
Key Equations
- ΔTb = i Kbm
- ΔTf = i Kfm
- Π = iMRT
Summary
Dissolution Process
A solution forms when two or more substances combine physically to yield a mixture that is homogeneous at the molecular level. The solvent is the most concentrated component and determines the physical state of the solution. The solutes are the other components typically present at concentrations less than that of the solvent. Solutions may form endothermically or exothermically, depending upon the relative magnitudes of solute and solvent intermolecular attractive forces. Ideal solutions form with no appreciable change in energy.
Solubility
The extent to which one substance will dissolve in another is determined by several factors, including the types and relative strengths of intermolecular attractive forces that may exist between the substances’ atoms, ions, or molecules. This tendency to dissolve is quantified as a substance’s solubility, its maximum concentration in a solution at equilibrium under specified conditions. A saturated solution contains solute at a concentration equal to its solubility. A supersaturated solution is one in which a solute’s concentration exceeds its solubility—a nonequilibrium (unstable) condition that will result in solute precipitation when the solution is appropriately perturbed. Miscible liquids are soluble in all proportions, and immiscible liquids exhibit very low mutual solubility. Solubilities for gaseous solutes decrease with increasing temperature, while those for most, but not all, solid solutes increase with temperature. The concentration of a gaseous solute in a solution is proportional to the partial pressure of the gas to which the solution is exposed, a relation known as Henry’s law.
Colligative Properties
Properties of a solution that depend only on the concentration of solute particles are called colligative properties. They include changes in the vapor pressure, boiling point, and freezing point of the solvent in the solution. The magnitudes of these properties depend only on the total concentration of solute particles in solution, not on the type of particles. The total concentration of solute particles in a solution also determines its osmotic pressure. This is the pressure that must be applied to the solution to prevent diffusion of molecules of pure solvent through a semipermeable membrane into the solution. Ionic compounds may not completely dissociate in solution due to activity effects, in which case observed colligative effects may be less than predicted.