Chapter 14: Solutions Concentration formulas Making a solution Freezing pt. depression Boiling pt. elevation Ch. 14 Concentration formulas Molarity Molality Equation M = mole of solute . m = mole of solute . Liter of solution kilogram of solvent Effects Depends on temp. Does not depend on temp. How do you make a solution? • Solvation: process of surrounding solute particles with solvent particles to form a solution • Heat of solution: overall energy change that occurs during the solution formation process Speed of dissolving • Solution formation depends on how much solute will dissolve in solvent. Affect on dissolving Stirring/ 1 agitation Stir/agitate Solute dissolves faster Increase temp Solute dissolves 2 Temperature faster Surface area 3 of solute Increase surface area Solute dissolves faster Surface area Solubility – amount of solute that dissolves in solvent at a given temp. and pressure Varying solubility of solution 1 Unsaturated solution Less solute than saturated solution 2 Saturated Solution Contains maximum amount of solute at given temp and pressure 3 Supersaturated solution Contains more solute than it can theoretically hold at given temp. and pressure Factors affecting solubility Simulation: Solubility and temp Factors affecting solubility •Increase temp • increase solubility of solids Temper1 ature •Allows supersaturated soln. to be made • decrease solubility of gases •Crystallization of supersaturated soln. initiated by •seed crystal •If container is scratched Factors affecting solubility Factors affecting solubility •Negligible for solubility of L and S 2 Pressure •Increase pressure gas increase solubility gas •(Henry’s Law) Section 2 Concentrations of Solutions Objective: Using Molarity (M) Change to moles!! 1. Mass of solute in grams 2. Amount of solute in mol 3. Volume of solute in L 4. Molar concentration, M 1. What is the molarity of a solution prepared by dissolving 37.94 g of potassium hydroxide in some water and then diluting the solution to a volume of 500.0 mL? Don’t Given: Unknown: forget to use moles! 2. Determine the molarity of a solution prepared by dissolving 141.6 g of citric acid, C3H5O(COOH)3 in water and then diluting the resulting solution to 3500.0 mL. Given: Unknown: 3. What is the molarity of a salt solution made by dissolving 280.0 mg of NaCl in 2.00 mL of water? Given: Unknown: mg… tricky? How do you get grams? Here’s a hint: 1g = 1000 mg 4. What is the molarity of a solution that contains 390.0 g of acetic acid, HC2H3O2, dissolved in enough acetone to make 1000.0 mL of solution? Given: Unknown: 5. An analytical chemist wants to make 750.0 mL of a 6.00 M solution of sodium hydroxide. What mass of NaOH will the chemist need to make this solution? Given: Unknown: 6. What mass of glucose, C6H12O6 would be required to prepare 5.000x103 L of a 0.215 M solution? Given: Unknown: Can you figure this out? 7. A solution has a volume of 2.0 L and contains 36.0 g of glucose (C6H12O6). If the molar mass of glucose is 180 g/mol. What is the molarity of the solution? Given: Unknown: 8. A solution has a volume of 250 mL and contains 0.70 mol NaCl. What is its molarity? Given: Unknown: This is CAKE ! Section 3: Colligative properties • Property that depends on amount of solute in solution, and not on identity of solution. Freezing point (FP) • Solute disrupts formation of orderly pattern; as a result, more kinetic energy must be withdrawn from a solution to cause solidification. * Solution that contains a solute has a lower Freezing point than the pure solvent Boiling point (BP) • Since adding a solute to a solvent decreases VP, additional kinetic energy must be added to raise VP and initiate boiling. * Solution that contains a solute has a higher boiling point than the pure solvent Factors affecting Colligative Properties 1. Increase amt. of solute, increase magnitude… a. VP lowering b. FP depression ~1 mol solute lowers FP by 1.86°C c. BP elevation ~ 1 mole solute increases BP by 0.512°C Factors affecting Colligative Properties 2. Solutes that dissociate have greater effects than nondissociating (nonpolar) solutes 3 particles Affect colligative property least 6 particles 9 particles Affect colligative property most Calculations with Colligative properties • Freezing pt. depression (FP dep) – difference in temperature between FP of solution and FP of pure solvent ΔTf = (Kf)(m) FP dep. example problems FP dep example 1: What is the freezing point depression (ΔTf) of a 0.100 m solution made with water? ΔTf = (Kf)(m) FP dep. Example 2: A solution made with ethanol is made to lower the freezing point by 6.10˚C. What is the molality of the solution? ΔTf = (Kf)(m) Calculations with Colligative properties • Boiling point elevation (BP elev.) – difference in temp between BP of a solution and BP of pure solvent ΔTb = (Kb)(m) BP dep. example problems BP elev. Example 1: What molality of NaCl solution would have to be used raise the boiling point of water by 2.00˚C? ΔTb = (Kb)(m) BP elev. Example 2: Determine BP elevation (ΔTb) of a 0.857 m CaCl2 solution? ΔTb = (Kb)(m)