Properties of Solutions 13.1 The Solution Process Solution – homogeneous mixture Solute – present in smaller quantity Solvent – present in larger quantity Intermolecular forces are rearranged when a solute and solvent are mixed. Will a solution form? Solute-solvent interaction must be stronger or comparable to the separation of solute and solvent particles. Intermolecular forces play a key role. Entropy (disorder) is also a factor. Disorder is favorable. (2nd law of thermodynamics) Solution formation increases entropy. Entropy in Solution Formation Ionic compound very ordered As the ionic compound dissolves, it becomes more disordered. An ionic crystal dissolving in water Saturated Solutions and Solubility Saturated solution – solution is in equilibrium with undissolved solute. dissolution Solute + solvent ⇌ solution crystallization Unsaturated – less solute than saturated Supersaturated – more solute than saturated A Saturated Solution A dynamic equilibrium – ions continually exchange between the solid and solution form. Factors affecting the rate of dissolving Higher temperatures Agitation by mixing Most solids dissovle better at higher temperatures Brings fresh solvent into contact with undissolved solid Decreasing the size of the particles Increases the surface area Factors Affecting Solubility 1. Like dissolves like, i.e. same polarity. Polar solutes are soluble in polar solvents. Nonpolar solutes are soluble in nonpolar solvents. If two liquids: miscible or immiscible Examples: ✔ Soluble: water + alcohol, NaCl + water, hexane + ✘ pentane Insoluble: water + hexane, NaCl + benzene, oil + water Factors Affecting Solubility 2. Molecular size. Larger molecules are more difficult to surround with solvent molecules in order to solvate the substance. 13.3 Factors Affecting Solubility 3. Temperature Effects For solids: Solubility ↑ as temperature ↑ (usually). For gases: Solubility ↓ as temperature ↑ (always). Ionic compounds Gases (In liquids) 13.3 Factors Affecting Solubility 4. Pressure Liquids and solids exhibit practically no change of solubility with changes in pressure. Only effects gases dissolved in liquid solvents. If the pressure is increased, the gas molecules are "forced" into the solution since this will best relieve the pressure that has been applied.