February 3rd 2016 Chapter 13 Chapter 11 12 HW due tonight Chapter 13 HW due Feb 13 Exam 1 Wednesday Non programmable calc Student ID Pencils Heat of Solution Ionic Solids in Water DHsoln DHsolute DHsolvent DHmix DHhydration always 0 M g or X g H2O DHsolute DHlattice always 0 MX s M g X g DHsoln DHlattice DHhydration M aq or X aq The Solution Process and the Change in Entropy The entropy S of a system is related to the number of ways a system can disperse its energy and therefore to the freedom of motion of the particles Sgas Sliquid Ssolid Change in entropy DS associated with a phase change DS Sf Si Example when liquid vaporizes to a gas DSvap Sgas Sliquid Sgas Sliquid so DSvap 0 A solution usually has higher entropy than the pure solute and pure solvent Ssoln Ssolute Ssolvent or DSsoln 0 An increase in entropy is favored in both physical and chemical processes 13 3 Solubility as an Equilibrium Process Solute undissolved D solute dissolved saturated solution contains the maximum amount of dissolved solute at a given temperature in the presence of undissolved solute unsaturated solution contains less than the equilibrium concentration of dissolved solute If more solute is added it will dissolve Figure 13 8 Sodium acetate crystallizing from a supersaturated solution supersaturated solution contains more than the equilibrium concentration of solute It is unstable and any disturbance will cause excess solute to crystallize immediately Factors that Effect Solubility Temperature Solids Most are more soluble at higher temperatures Gases Solubility of any gas in water decreases with rising temperature Exothermic Process Factors that Effect Solubility Pressure Gases Solubility of any gas in water increases at higher pressure Sgas kH Pgas Henry s Law The solubility of a gas Sgas is directly proportional to the partial pressure of the gas Pgas above the solution Sample Problem 13 2 Using Henry s Law to Calculate Gas Solubility The partial pressure of CO2 gas inside a bottle of cola is 4 atm at 25 oC What is the solubility of CO2 The Henry s law constant for CO2 dissolved in water is 3 3 x 10 2 mol L atm at 25 oC SOLUTION Sgas kH Pgas S 3 3 x 10 2 mol L atm 4 atm 0 1 mol L CO2 The solubility of of O2 in water at 25 C is 2 86 10 4 mol L What is the partial pressure of the gas kH at 25 C 1 3 10 3 mol L atm A 0 22 atm B 4 54 atm C 2 2 atm SO2 kH PO2 D 0 454 atm E 1 atm PO2 SO2 kH PO2 2 86 10 4 mol L 1 3 10 3 mol L atm PO2 0 22 atm 13 4 Concentration Terms Concentration Term amount mol of solute volume L of solution Molarity M amount mol of solute Molality m mass kg of solvent Parts by mass mass ppm Parts by volume volume Mole fraction X Ratio mass of solute mass of solution 100 volume of solute volume of solution 106 100 amount mol of solute amount mol of solute amount mol of solvent Sample Problem 13 4 Expressing Concentrations in Parts by Mass Parts by Volume and Mole Fraction a Find the concentration of calcium in ppm in a 3 50 g pill that contains 40 5 mg of Ca2 1g 2 40 5 mg Ca 103 mg 106 1 16 104 ppm Ca2 3 50 g b The label on a 0 750 L bottle of Italian chianti indicates 11 5 alcohol by volume How many liters of alcohol does the wine contain 0 750 L chianti 11 5 L alcohol 100 L chianti 0 0862 L alcohol Sample Problem 13 5 Interconverting Concentration Terms Hydrogen peroxide is a powerful oxidizing agent used in concentrated solution in rocket fuels and in dilute solution as a hair bleach An aqueous solution H2O2 is 30 0 by mass and has a density of 1 11 g mL Calculate its a Molality mol solute kg solvent 30 0 g H2O2 x 1 mol H2O2 34 02 g H2O2 0 882 mol H2O2 kg of H2O 100 g solution 30 0 g H2O2 70 0 g H2O 0 07 kg H2O molality 0 882 mol H2O2 12 6 m H2O2 0 07 kg mol solute c Molarity L solution volume of solution 100 0 g x molarity mol H2O2 L soln 1 mL 1 11 g 90 1 mL 0 0901 L 0 882 mol H2O2 0 0901 L 9 79 M H2O2