Properties of Solutions

A solution is a homogenous mixture of 2 or more substances. The solute is(are) the substance(s) present in the smaller amount(s). The solvent is the substance present in the larger amount.

An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity. A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity. nonelectrolyte weak electrolyte strong electrolyte

A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature. An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature. A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature. Sodium acetate crystals rapidly form when a seed crystal is added to a supersaturated solution of sodium acetate.

Concentration Units The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. Molarity (M) M = moles of solute liters of solution

The Energies of Solution Formation

Three types of interactions in the solution process: solute-solute interaction (separating the solute) solvent-solvent interaction (overcoming intermolecular forces) solvent-solute interaction

Steps 1 and 2 require energy, since forces must be overcome to expand the solute and solvent. Step 3 usually releases energy. Steps 1 and 2 are endothermic and step 3 is often exothermic. Enthalpy change: enthalpy (heat) of solution (∆Hsoln) is the sum of the ∆H values for the steps: ∆Hsoln = ∆H1 + ∆H2 + ∆H3

(a) ΔHsoln has a negative sign (exothermic) if step 3 releases more energy than that required by 1 and 2 (b) ΔHsoln has a positive sign (endothermic) if steps 1 and 2 require more energy than is released in 3

What factors affect solubility? “like dissolves like” Two substances with similar intermolecular forces are likely to be soluble in each other. non-polar molecules are soluble in non-polar solvents CCl4 in C6H6 polar molecules are soluble in polar solvents C2H5OH in H2O ionic compounds are more soluble in polar solvents NaCl in H2O or NH3 (l)

Factors Affecting Solubility Temperature Pressure

Temperature and Solubility Solid solubility and temperature – the solubility of most solids increases with temperature. solubility increases with increasing temperature solubility decreases with increasing temperature due to entropy (not covered yet)

Temperature and Solubility Gas solubility and temperature solubility usually decreases with increasing temperature (more energy to escape from solvent)

A suspension of tiny particles in some medium is called a colloidal dispersion, or a colloid. Colloids The Tyndall effect is used to distinguish between a suspension and a true solution. Light is scattered by the suspended particles in a colloid.  Dispersion Medium  Dispersed Phase  Type of colloid  Example  Gas  Liquid  Aerosol  Fog, mist  Solid  Smoke  Foam  Whipped cream  Emulsion  Mayonnaise, hair cream  Sol  Paints, cell fluids  Pumice, plastic foams  Gel  Jelly, cheese  Solid Sol  Ruby glass (glass with dispersed metal)