7.2 Solubility Mixing Solute and Solvent

Solutions I II III 7.2 Solubility Mixing solute and solvent “Like Dissolves Like” NONPOLAR POLAR NONPOLAR POLAR FACTORS THAT AFFECT RATE OF SOLUTION FORMATION Three factors that determine the rate a which a solute dissolves are stirring (agitation), temperature, and the particle size of the solute. STIRRING/AGITATION Stirring a solution speeds up the rate of dissolving because it disperses the solute and brings the solute in contact with all of the solvent particles. TEMPERATURE Increasing the temperature of the solution usually increases the rate at which a solid solute dissolves because the particles are moving faster. PARTICLE SIZE/SURFACE AREA Dissolving only occurs at the surface of a particle. The smaller the particles, the more surface area the solvent can dissolve. SOLUBILITY Solubility is the amount of solute that dissolves in a given quantity of solvent at a specific temperature. Solubility is often expressed in grams of solute per 100g of solvent. The stronger the attractions between the solute and solvent molecules, the greater the solubility. UNSATURATED An unsaturated solution contains less than the maximum amount of solute at a given temperature. If more solute is added, then it will dissolve. SATURATED A saturated solution contains the maximum amount of solute at a given temperature. If more solute is added, then it will settle at the bottom. SUPERSATURATED A supersaturated solution contains more than the maximum amount of solute at a given temperature. A supersaturate solution is extremely unstable. If more solute is added, then a fast recrystallization of the previously dissolved solute occurs. SUPERSATURATED Solubility of a solid solute tends to increase with temperature. A supersaturated solution is made by heating the solvent and adding the maximum amount of solute at the elevated temperature. If the solution is CAREFULLY cooled, then you can form a supersaturated solution. SOLUBILITY COMPARISON UNSATURATED SOLUTION more solute dissolves SATURATED SOLUTION no more solute dissolves concentration SUPERSATURATED SOLUTION becomes unstable, crystals form LIQUID SOLUTIONS Two liquids that will dissolve each other are miscible. Ex: vinegar and water Two liquids that will not dissolve one another are immiscible. Ex: oil and water FACTORS AFFECTING THE SOLUBILITY OF A GAS As temperature increases, the solubility of a gas tends to decrease. The gas particles need to be as slow as possible to force them into a liquid solvent. As pressure increases, the solubility of a gas tends to increase because we are forcing the particles into the liquid. FACTORS AFFECTION SOLUBILITY OF A SOLID As temperature increases, the solubility of a solid solute tends to increase. A change in pressure does not affect the solubility of a solid solute. C. SOLUBILITY Solubility Curve: shows the dependence of solubility on temperature 1)What is the solubility of sodium nitrate in at 30°C in: a. 100 g H2O __________________ b. 450 g H2O ___________________ c. 25 g H2O ____________ 2) How many grams of ammonium chloride will precipitate out of solution if it is cooled from 70°C t0 50°C in 100 g of H2O? 3) What is the solubility of potassium nitrate at 110 °C? What is the mass percent of this solution? If the density of aqueous potassium nitrate is 1.20 g/mL, what is the Molarity? 3)Which salt is least soluble at 20°C? ________ Which salt is most soluble at 20 °C? ________ 4) Which of the substances are gases? How do we know? 5) Which gas is most soluble at 50°C? ________ 6)Determine if the following solutions are saturated, unsaturated or supersaturated: a. 40 g of KCl in 100 g of water at 80°C_________ b. 120 g of KNO3 in 100 g of water at 60°C ______ c. 10 g of KClO3 in 100 g of water at 20°C ______ SECTION 7.2 1. What units are usually used to express the solubility of a solute? 2. What would you do to change a saturated solution to an unsaturated solution? Work on Practice: 7.2 Solubility Curves