Physical Properties of Solutions Chapter 13

Factors Affecting Solubility Glucose (which has hydrogen bonding) is very soluble in water Cyclohexane (which only has dispersion forces) is not Fig Structure and solubility

Pressure Effect on Gases in Solution Solubility of liquids and solids does not change appreciably with pressure Solubility of a gas in a liquid is directly proportional to its pressure Fig Effect of pressure on gas solubility

Henry’s Law S g = kP g where S g ≡ solubility of the gas k ≡ the Henry’s Law constant for that gas in that solvent P g ≡ partial pressure of the gas above the liquid Fig Solubility decreases as pressure decreases

Temperature Effect on Solids and Liquids Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature Fig Solubilities of several ion compounds as a function of temperature

The opposite is true of gases: Carbonated soft drinks are more “bubbly” if stored in the refrigerator Warm lakes have less O 2 dissolved in them than cool lakes Temperature Effect on Gases Fig Variation of gas solubility with temperature

Concentration Units Mass percentage Mole fraction ppm and ppb Molarity Molality Concentration - amount of solute present in a given quantity of solvent or solution:

Concentration Units Mass percentage (w/w) % by mass = x 100% mass of solute mass of solute + mass of solvent = x 100% (w/w) mass of solute mass of solution Mole Fraction (X) X A = moles of A sum of moles of all components

(a)Calculate the mass percentage of NaCl in a solution containing 1.50 g of NaCl in 50.0 g of water. (b) A commercial bleaching solution contains 3.62 mass % sodium hypochlorite, NaOCl. What is the mass of NaOCl in a bottle containing 2.50 kg of bleaching solution? Answer: (a) 2.91% (b) 90.5 g of NaOCl Practice Exercise p 543

An aqueous solution of hydrochloric acid contains 36% HCl by mass. Calculate the mole fraction of HCl in the solution. Sample Exercise 13.6 Calculation of Mole Fraction Assume we have 100. g of solution:

Parts per million (ppm) Parts per billion (ppb) Concentration Units Continued

M = moles of solute liters of solution Molarity (M) Molality (m) m = moles of solute mass of solvent (kg)

What is the molality of a solution made by dissolving 36.5 g of naphthalene (C 10 H 8 ) in 425 g of toluene (C 7 H 8 )? Answer: m Practice Exercise p 544

Conversion of Concentration Units If we know the density of the solution, we can calculate the molality from the molarity and vice versa. Fig Calculating molality and molarity

What is the molality of a 5.86 M ethanol (C 2 H 5 OH) solution whose density is g/mL? m =m = moles of solute mass of solvent (kg) M = moles of solute liters of solution Assume 1 L of solution: 5.86 moles ethanol = 270 g ethanol 927 g of solution (1000 mL) (0.927 g/mL) mass of solvent = mass of solution – mass of solute = 927 g – 270 g = 657 g = kg m =m = moles of solute mass of solvent (kg) = 5.86 moles C 2 H 5 OH kg solvent = 8.92 m