DescriptionSolutions are homogeneous (evenly distributed) mixtures that form when a solute is dissolved or mixed with a solvent. To form a solution, solute particles must spread apart from one another, and solvent particles must spread apart from one another. Solute and solvent particles must then move together through an attractive intermolecular force. Solute and solvent particles must have similar structures and have intermolecular forces of similar strengths in order to form a homogeneous mixture. Ionic compounds are soluble in water because the high bond energy of ionic crystals is overcome by the hydration energy of the ion-dipole bond (attraction between an ion and a particle with partially charged ends) between ions and water. Colligative properties are a set of solution properties that are affected only by the concentration of the solution (number of particles present in the solution). Colligative properties include freezing point depression, boiling point elevation, vapor pressure reduction, and osmotic pressure. A mixture is a colloid if it is heterogeneous (unevenly distributed) with suspended particles that do not settled.
At A Glance
- Solutions are homogeneous mixtures of two or more substances that have an enthalpy change (heat absorbed or released) associated with their formation.
- Solutions will form only if solute and solvent particles have similar intermolecular forces.
- Ionic compounds dissolve in water if the energy released by hydration is similar in magnitude to the energy holding the ionic crystal together.
- Temperature changes affect the solubility of solids and gases differently. The solubility of solids increases with increasing temperature. Gas solubility decreases with increasing temperature.
- The total vapor pressure of a solution is the sum of the partial pressures of the individual gas components.
- Concentration reported as molality (moles of solute divided by the mass in kilograms of the solvent) and mole fraction (moles of solvent divided by moles of solution) is independent of the volume of the solvent.
- The vapor pressures and melting points of solutions are lower than those of the pure solvent. The boiling points are elevated.
- The increased mole number introduced by dissociated ions affects the colligative properties of a solution.
- The reduced vapor pressure in a solution is responsible for distillation (separation of liquids by boiling) and osmotic pressure (pressure needed to stop the flow of water through a semipermeable membrane).
- Colloids are heterogeneous (unevenly distributed) mixtures in which suspended particles do not settle.