Solubility There is a limit to the amount of solute that can be dissolved in a solvent. The point at which this limit is reached for any solute-solvent combination depends on the nature of the solute the amount of the solvent the temperature

Saturated Versus Unsaturated Solutions A solution that contains the maximum amount of dissolved solute is described as a saturated solution. If more solute is added to a saturated solution, it falls to the bottom of the container and does not dissolve. A solution that contains less solute than a saturated solution under the same conditions is an unsaturated solution.

Supersaturated Solutions Usually when a saturated solution is cooled, the excess solute usually comes out of solution, leaving the solution saturated at the lower temperature. But sometimes the excess solute does not separate and forms a supersaturated solution. solution that contains more dissolved solute than a saturated solution contains under the same conditions. application: rock candy

Supersaturated Solutions

Solubility Values The solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature. example: The solubility of sodium chloride is 36 g per 100 g of water at 20°C. Solubilities vary widely and are determined experimentally. They can be found in chemical handbooks and are usually given as grams of solute per 100 g of solvent at a given temperature.

Solubilities of Some Substances in Water at Various Temperatures (g solute / 100 g H2O) Formula 0°C 20°C 50°C 100°C lithium carbonate Li2CO3 1.5 1.3 1.1 0.70 potassium chloride KCl 27.6 34.0 42.6 57.6 sodium chloride NaCl 35.7 36.0 37.0 39.2 sodium nitrate NaNO3 74.0 88.0 114.0 182.0 silver nitrate AgNO3 122.0 222.0 455.0 733.0 sucrose C12H22O11 179.0 230.9 260.4 487.0

Factors Affecting Solubility Temperature Increasing the temperature usually increases solubility of solids in liquids. The effect of temperature on solubility for a given solute is difficult to predict. The solubilities of some solutes vary greatly over different temperatures, and those for other solutes hardly change at all. A few solid solutes are actually less soluble at higher temperatures. b) Increasing the temperature usually decreases the solubility of a gas in liquid.

Solubility curve – graph that represents the relationship between the solubility of a substance and its temperature.

Pressure Changes in pressure have little effect on the solubility of solids and liquids in liquid solvent, but pressure strongly influences the solubility of gases. Solubility of gas in liquid solvent increases as the pressure above the solution increases. Therefore, at a given temperature, the solubility of a gas is directly proportional to the pressure of the gas above the liquid This relationship is known as Henry’s law.

Application – carbonate beverages – solubility of CO2 increased by bottling solution at a pressure of 5-10 atm. When opened, the pressure is reduced and the solubility of the CO2 decreases. This rapid escape of the gas from the liquid solution is known as effervescence.

Liquid Solutes and Solvents Immiscible – liquids that are not soluble in each other Ex. – oil (nonpolar) and water (polar)– strong H- bonding between water molecules squeezes out oil droplets

Miscible – liquids that dissolve freely in each other in any proportion Nonpolar substances such as fats, oils, are generally quite soluble in nonpolar liquids, such as tetrachloride, toluene, and gasoline. These liquids are nonpolar and only have weak London dispersion forces. The IMFs are similar to those in a pure substance, so the molecules freely mix.

Enthalpies of Solution The formation of a solution is accompanied by an energy change. Ex – outside of beaker feels warm (exothermic) or cold (endothermic) Solvent is held together by IMFs (solvent-solvent attraction) Solute is held together by IMFs (solute-solute attraction)

Three Steps in Solution Formation Energy is required to separate solute molecules and solvent molecules from their neighbors. Three Steps in Solution Formation Solute particles being separated. (Endothermic) Solvent particles being moved apart to allow solute particles to enter. (Endothermic) Solvent particles being attracted to and solvating solute particles. (Exothermic)

Enthalpy of Solution ΔHsoln – the net amount of energy absorbed as heat by the solution when a specific amount of solute dissolves in a solvent. Negative (energy is released) - sum of attractions from steps 1 and 2 is less than step 3. Positive (energy is absorbed) – sum of attractions from steps 1 and 2 is greater than step 3.

Wrapping It Up Reflect on what you have learned concerning the today’s topic. Respond to the following… What is the most important thing you learned today? What is one question you would still like answered? What is the one way what you have learned connects with what you knew before?