#### Transcript Chapter 11: Solutions and Their Properties

Chapter 11b: Solutions and Their Properties Introduction 1. A mixture is any intimate combination of two or more pure substances 2. Can be classified as heterogeneous or homogeneous Heterogeneous -The mixing of components is visually nonuniform and have regions of different composition Homogenous -Mixing is uniform, same composition throughout -Can be classified according to the size of their particles as either solutions or colloids What is a solution? Sugar + water Solution Formation Solute • Dissolved substance, or smaller quantity substance Solvent • Liquid dissolved in, larger quantity substance Saturated solution • Contains the maximum amount of solute that will dissolve in a given solvent. Solution Formation Unsaturated Contains less solute than a solvent has the capacity to dissolve. Supersaturated Contains more solute than would be present in a saturated solution. Crystallization The process in which dissolved solute comes out of the solution and forms crystals. Units of Concentration Molarity; Mole Fraction; Mass percentage; Molality. Units of Concentration Molarity (M) M = mole of solute / Liter of solution Molality (m) m = moles of solute/mass of solvent (kg) Mole Fraction (x) X = mole of component / total moles Units of Concentration Mass Percent (mass %) Mass % = (mass of component / total mass of sol’n) x 100% Parts per million, ppm = (mass of component / total mass of solution) x 106 Parts per billion, ppb = (mass of component / total mass of solution) x 109 Molarity (M) Advantage: amounts of solute can be measured by volume rather than by mass. Disadvantage: Exact concentration depends on temperature Because the volume of a solution expands or contracts as the temperature changes. • Mass percentage: Mass% = mass of component -----------------------x 100% total mass of solution What is the mass percentage of glucose in a solution prepared by dissolving 10g of glucose into 100g of water? 10 g Mass % glucose = -------------- x 100% = 9.09 mass% 10g + 100g For traces: Parts per million ppm mass of component ppm = ---------------------------total mass of solution 1 ppm = 1 mg/L x 106 Parts per billion ppb ppb = mass of component ---------------------------total mass of solution 1 ppb = 1 mg/L or 1 mg/1000L x 109 Molality (m) moles of solute m = ----------------------mass of solvent (kg) For a 1 m solution of KBr dissolve 1 mol KBr (119g) in 1 kg water. Advantage: Disadvantage: only masses, independent on temp. amounts must be measured by mass and not by volume What is the molality of a solution prepared by dissolving 0.385 g of cholesterol, C27H46O in 40.0 g of chloroform, CHCl3? Cholesterol = 386.7 amu ; chloroform = 119.4 amu What is the mole fraction of cholesterol in the solution? What is the molality of a solution prepared by dissolving 0.385 g of cholesterol, C27H46O in 40.0 g of chloroform, CHCl3? Cholesterol = 386.7 amu ; chloroform = 119.4 amu moles cholesterol 0.385g / 386.7 Molality = ---------------------------- = ----------------------- = 0.0249 mol/kg kg chloroform 0.04 kg What is the mole fraction of cholesterol in the solution? 0.385g / 386.7 Xchloroform = -------------------------------- = 2.96 x 10-3 0.385g/386.7 + 40/119.4 Assuming that seawater is an aqueous solution of NaCl what is its molarity? The density of seawater is 1.025 g/mL at 20C and the NaCl concentration is 3.50 mass % Assuming that seawater is an aqueous solution of NaCl what is its molarity? The density of seawater is 1.025 g/mL at 20C and the NaCl concentration is 3.50 mass % 3.5 mass% = 35 g NaCl in 1 kg solution 1 kg solution = m/d = 1000/1.025 = 975.6 mL 35 g / (23+35.5) 0.598 Molarity = --------------------- = ----------- = 0.61 mol/L = 0.61 M 0.9756 L 0.9756 Example 3 What is the mass % concentration of a saline sol’n prepared by dissolving 1.00 mol of NaCl in 1.00 L of water? DensityH2O=1.00 g/mL MMNaCl = 58.443 g/mol Ans: 5.52% Example 4 Assuming that seawater is an aqueous solution of NaCl what is its molarity? The density of seawater is 1.025 g/mL at 20C and the NaCl concentration is 3.50 mass % • Assume 1 L to make easier, 1000 mL • Ans: 0.615M Example 5 What is the molality of a solution prepared by dissolving 0.385 g of cholesterol, C27H46O in 40.0 g of chloroform, CHCl3? What is the mole fraction of cholesterol in the solution? • Ans: m = 0.0249m , X = 2.96 x 10-3 Example 6 What mass in grams of a 0.500 m solution of sodium acetate, CH3CO2Na, in water would you use to obtain 0.150 mol of sodium acetate? • Assume 1 kg Example 7 The density at 20°C of a 0.258 m solution of glucose in water is 1.0173 g/mL and the molar mass of glucose is 180.2 g/mol. What is the molarity of the solution? • Assume 1 kg Example 8 The density at 20°C of a 0.500 M solution of acetic acid in water is 1.0042 g/mL. What is the concentration of this solution in molality? The molar mass of acetic acid, CH3CO2H, is 60.05 g/mol. • Assume 1 L • 1.36 g of MgCl2 are dissolved in 47.46 g of water to give a solution with a final volume of 50.00 mL. Calculate the concentration of the solution in mass %, ppm, mole fraction, molarity, and molality. • Hydrochloric acid is sold as a concentrated aqueous solution. The concentration of commercial HCl is 11.7 M and its density is 1.18 g/mL. Calculate the mass percent of HCl in the solution. Calculate the molality of the solution. • Concentrated sulfuric acid has a density of 1.84 g/mL and is 18 M. What is the mass % H2SO4 in the solution? What is the molality of H2SO4 in the solution?