Solution Properties 11.1 Solution Composition 11.2 The Energies of Solution Formation 11.3 Factors Affecting Solubility 11.4 The Vapor Pressures of Solutions 11.5 Boiling-Point Elevation and Freezing-Point Depression 11.6 Osmotic Pressure 11.7 Colligative Properties of Electrolyte Solutions 11.8 Colloids

Various Types of Solutions Example State of Solution State of Solute State of Solvent Air, natural gas Gas Vodka, antifreeze Liquid Brass Solid Carbonated water (soda) Seawater, sugar solution Hydrogen in platinum

Solution Composition

Exercise #1 You have 1.00 mol of sugar in 125.0 mL of solution. Calculate the concentration in units of molarity. 8.00 M

Exercise #2 You have a 10.0 M sugar solution. What volume of this solution do you need to have 2.00 mol of sugar? 0.200 L

Exercise #3 Consider separate solutions of NaOH and KCl made by dissolving 100.0 g of each solute in 250.0 mL of solution. Calculate the concentration of each solution in units of molarity. 10.0 M NaOH 5.37 M KCl

Exercise #4 What is the percent-by-mass concentration of glucose in a solution made my dissolving 5.5 g of glucose in 78.2 g of water? 6.6%

Exercise #5 A solution of phosphoric acid was made by dissolving 8.00 g of H3PO4 in 100.0 mL of water. Calculate the mole fraction of H3PO4. (Assume water has a density of 1.00 g/mL.) 0.0145

Exercise #6 A solution of phosphoric acid was made by dissolving 8.00 g of H3PO4 in 100.0 mL of water. Calculate the molality of the solution. (Assume water has a density of 1.00 g/mL.) 0.816 m

Formation of a Liquid Solution Separating the solute into its individual components (expanding the solute). Overcoming intermolecular forces in the solvent to make room for the solute (expanding the solvent). Allowing the solute and solvent to interact to form the solution.

Steps in the Dissolving Process

Steps in the Dissolving Process Steps 1 and 2 require energy, since forces must be overcome to expand the solute and solvent. Step 3 usually releases energy. Steps 1 and 2 are endothermic, and step 3 is often exothermic.

Enthalpy (Heat) of Solution Enthalpy change associated with the formation of the solution is the sum of the ΔH values for the steps: ΔHsoln = ΔH1 + ΔH2 + ΔH3 ΔHsoln may have a positive sign (energy absorbed) or a negative sign (energy released).

Enthalpy (Heat) of Solution

Concept Check Explain why water and oil (a long chain hydrocarbon) do not mix. In your explanation, be sure to address how ΔH plays a role.

The Energy Terms for Various Types of Solutes and Solvents Hsoln Outcome Polar solute, polar solvent Large Large, negative Small Solution forms Nonpolar solute, polar solvent Large, positive No solution forms Nonpolar solute, nonpolar solvent Polar solute, nonpolar solvent

In General One factor that favors a process is an increase in probability of the state when the solute and solvent are mixed. Processes that require large amounts of energy tend not to occur. Overall, remember that “like dissolves like”.

Factors Affecting Solubility Structural Effects: Polarity – “like dissolves like” Pressure Effects: Henry’s law – for solubility of gases Temperature Effects: Affecting aqueous solutions

Pressure Effects Henry’s law: c = kP c = concentration of dissolved gas k = constant P = partial pressure of gas solute above the solution Amount of gas dissolved in a solution is directly proportional to the pressure of the gas above the solution.

A Gaseous Solute

Temperature Effects (for Aqueous Solutions) Although the solubility of most solids in water increases with temperature, the solubilities of some substances decrease with increasing temperature. Predicting temperature dependence of solubility is very difficult. Solubility of a gas in solvent typically decreases with increasing temperature.

The Solubilities of Several Solids as a Function of Temperature

The Solubilities of Several Gases in Water

Ideal Solution: One that obeys Raoult’s Law

Vapor Pressures of Solutions of Nonvolatile Solutes Nonvolatile solute lowers the vapor pressure of solvent. Raoult’s Law: Psoln = vapor pressure of solution solv = mole fraction of solvent = vapor pressure of pure solvent

Ideal Solutions Consisting of Two Volatile Liquids Two volatile Liquids form ideal solution if: they are structurally very similar, and molecular interactions between nonidentical molecules were relatively similar to identical molecules. The vapor of each liquid obeys Raoult’s Law: PA = XAPoA; PB = XBPoB PT = PA + PB = XAPoA + XBPoB (X : mole fraction; Po : vapor pressure of pure liquid)

Summary of the Behavior of Various Types of Solutions of Two Volatile Liquids Interactive Forces Between Solute (A) and Solvent (B) Particles Hsoln T for Solution Formation Deviation from Raoult’s Law Example A  A, B  B  A  B Zero None (ideal solution) Benzene-toluene A  A, B  B < A  B Negative (exothermic) Positive Negative Acetone-water A  A, B  B > A  B Positive (endothermic) Ethanol-hexane

Vapor Pressure for a Solution of Two Volatile Liquids

Laboratory Fractional Distillation Apparatus

Fractional Distillation Towers in Oil Refinaries

Refined Crude Oil Mixtures

Concept Check For each of the following solutions, would you expect it to be relatively ideal (with respect to Raoult’s Law), show a positive deviation, or show a negative deviation? Hexane (C6H14) and chloroform (CHCl3) Ethyl alcohol (C2H5OH) and water Hexane (C6H14) and octane (C8H18)

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Exercise #7 (a) The mole fractions of benzene and toluene; A solution of benzene (C6H6) and toluene (C7H8) contains 50.0% benzene by mass. The vapor pressures of benzene and pure toluene at 25oC are 94.2 torr and 28.4 torr, respectively. Assuming ideal behavior, calculate the following: (a) The mole fractions of benzene and toluene; (b) The vapor pressure of each component in the mixture, and the total vapor pressure above the solution. (c) The composition of the vapor in mole percent.

Exercise #8 A solution composed of 24.3 g acetone (CH3COCH3) and 39.5 g of carbon disilfide (CS2) has a measured vapor pressure of 645 torr at 35oC. (a) Is the solution ideal or nonideal? (b) If not, does it deviate positively or negatively from Raoult’s law? (c) What can you say about the relative strength of carbon disulfide-acetone interactions compared to the acetone-acetone and carbon disulfide-carbon disulfide interaction? (Vapor pressures at 35oC of pure acetone and pure carbon disulfide are 332 torr and 515 torr, respectively.)