Chemistry: Atoms First Second Edition Julia Burdge & Jason Overby Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 13 Physical Properties of Solutions M. Stacey Thomson Pasco-Hernando State College

What happens when you mix substances together? If the substances are relatively stable, they will simply occupy the same container. Relative strengths of the attractions below will primarily determine whether a solution will form A Molecular View of the Solution Process Solvation involves specific types of interactions between substances. 1) Solute-solute interactions 2) Solvent-solvent interactions 3) Solute-solvent interactions 13.2

A Molecular View of the Solution Process SoluteSolvent Separated solute Separated solvent Solution Energy Step 2 ΔH 2 > 0 Step 1 ΔH 1 > 0 Step 3 ΔH 3 < 0 ΔH soln > 0 ΔH soln = ΔH 1 + ΔH 2 + ΔH 3

Depending on their intermolecular attractions, they may make a HOMOgeneous mixture or a HETEROgeneous mixture. Recall all of the intermolecular attractions we discussed in chapter 12. A Molecular View of the Solution Process

The Importance of Intermolecular Forces Components of a mixture can have different properties, there is a greater variety of intermolecular forces to consider.

“Like dissolves like” Two substances with similar type and magnitude of intermolecular forces are likely to be soluble in each other. The Importance of Intermolecular Forces Toluene, C 7 H 8 Octane, C 8 H 18 Both non-polar liquids, solution forms when mixed Two liquids are said to be miscible if they are completely soluble in each other in all proportions.

“Like dissolves like” Two substances with similar type and magnitude of intermolecular forces are likely to be soluble in each other. The Importance of Intermolecular Forces Polar and non-polar liquids, solution does not form when mixed Water, H 2 O Octane, C 8 H 18

“Like dissolves like” Two substances with similar type and magnitude of intermolecular forces are likely to be soluble in each other. Text Practice: The Importance of Intermolecular Forces Ethanol, C 2 H 6 O Both polar liquids, solution forms when mixed Water, H 2 O

Worked Example 13.1 Strategy Consider the structure of each solute to determine whether or not it is polar. For molecular solutes, start with a Lewis structure and apply the VSEPR theory. We expect polar solutes, including ionic compounds, to be more soluble in water. Nonpolar solutes will be more soluble in benzene. Determine for each solute whether the solubility will be greater in water, which is polar, or in benzene (C 6 H 6 ), which is nonpolar: (a) Br 2, (b) sodium iodide (NaI), (c) carbon tetrachloride, and (d) formaldehyde (CH 2 O).

Types of Solutions A solution is a homogeneous mixture of two or more substances. A solution consists of a solvent and one or more solutes. 13.1

Pressure greatly influences the solubility of a gas. Henry’s law states that the solubility of a gas in a liquid is proportional to the pressure of the gas over the solution. cmolar concentration (mol/L) P pressure (atm) kproportionality constant called Henry’s law constant Text Practice: Factors That Affect Solubility c = kP

Solution formation or Solvation Water is a good solvent for ionic compounds because it is a polar molecule. The polarity of water results from electron distributions within the molecule. The oxygen atom has an attraction for the hydrogen atoms’ electrons and is therefore partially negative compared to hydrogen.    –– The oxygen atom is partially negative The hydrogen atoms are partially positive   

Solution Formation Hydration occurs when water molecules remove the individual ions from an ionic solid surrounding them so the substances dissolves. ncord.org/public/student/solution/watershell.htmlhttp://mw.concord.org/modeler/showcase/simulation.html?s= ncord.org/public/student/solution/watershell.html

Factors That Affect Solubility Temperature affects the solubility of most substances. 13.4

Electrolytes and Nonelectrolytes An electrolyte is a substance that dissolves in water to yield a solution that conducts electricity. An electrolyte undergoes dissociation and breaks apart into its constituent ions. NaCl(s) Na + (aq) + Cl – (aq) H2OH2O 9.1

Electrolytes and Nonelectrolytes A nonelectrolyte is a substance that dissolves in water to yield a solution that does not conduct electricity. The sucrose molecules remain intact upon dissolving. /sugar-and-salt-solutionshttps://phet.colorado.edu/en/simulation /sugar-and-salt-solutions C 12 H 22 O 11 (s) C 12 H 22 O 11 (aq) H2OH2O

Electrolytes and Nonelectrolytes An electrolyte that dissociates completely is known as a strong electrolyte. Water soluble ionic compounds Strong Acids Strong Bases HCl(g) H + (aq) + Cl – (aq) H2OH2O NaOH(s)Na + (aq) + OH – (aq) H2OH2O NaCl(s) Na + (aq) + Cl – (aq) H2OH2O

Strong Electrolytes and Weak Electrolytes A weak electrolyte is a compound that produces ions upon dissolving but exists in solution predominantly as molecules that are not ionized. Weak Acids Weak Bases HC 2 H 3 O 2 (l) H + (aq) + C 2 H 3 O 2 (aq) – NH 4 (aq) + OH – (aq) NH 3 (g) + H 2 O(l) +

Strong Electrolytes and Weak Electrolytes The double arrow,, denotes a reaction that occurs in both directions. When both the forward and reverse reactions occur at the same rate, the reaction is in a state of dynamic chemical equilibrium. hill.com/sites/ /student_view0/chapter9/animations.html# hill.com/sites/ /student_view0/chapter9/animations.html#

Worked Example 9.1 Sports drinks typically contain sucrose (C 12 H 22 O 11 ), fructose (C 6 H 12 O 6 ), sodium citrate (Na 3 C 6 H 5 O 7 ), potassium citrate (K 3 C 6 H 5 O 7 ), and ascorbic acid (H 2 C 6 H 6 O 6 ), among other ingredients. Classify each of these ingredients as a nonelectrolyte, a weak electrolyte, or a strong electrolyte.

Solutions can be classified by the amount of solute dissolved. An unsaturated solution is one that contains less solute than the solvent has the capacity to dissolve at a specific temperature. Types of Solutions

Solutions can be classified by the amount of solute dissolved. A saturated solution is one that contains the maximum amount of solute that will dissolve in a solvent at a specific temperature. Types of Solutions

Supersaturated solutions are generally unstable. Types of Solutions

Precipitation Processes An insoluble product that separates from a solution is called a precipitate. 2NaI(aq) + Pb(NO 3 ) 2 (aq) PbI 2 (s) + 2NaNO 3 (aq) 9.2

Precipitation Reactions In a molecular equation compounds are represented by chemical formulas as though they exist in solution as molecules or formula units. Na 2 SO 4 (aq) + Ba(OH) 2 (aq) 2NaOH(aq) + BaSO 4 (s)

Precipitation Reactions In the reaction between aqueous Na 2 SO 4 and Ba(OH) 2 the aqueous species are represented as follows: In an ionic equation compounds that exist completely or predominately as ions in solution are represented as those ions. Na 2 SO 4 (aq) → 2Na + (aq) + SO 4 (aq) 2– Ba(OH) 2 (aq) → Ba 2+ (aq) + 2OH – (aq) NaOH(aq) → Na + (aq) + OH – (aq) 2Na + (aq) + SO 4 (aq) + Ba 2+ (aq) + 2OH – (aq) 2Na + (aq) + 2OH – (aq) + BaSO 4 (s) 2– Na 2 SO 4 (aq) + Ba(OH) 2 (aq) 2NaOH(aq) + BaSO 4 (s)

Study Guide for Sections 13.2, 13.1, 13.4, DAY 25, Terms to know: Sections 13.2, 13.1, 13.4, 9.1, 9.2 solution, solvent, solute, solvation, solute-solute interactions, solvent-solvent interactions, solvent-solute interactions, miscible, saturated solution, unsaturated solution, supersaturated solution, Henry’s Law, electrolyte, precipitate, molecular equation, ionic equation DAY 25, Specific outcomes and skills that may be tested on exam 4: Sections 13.2, 13.1, 13.4, 9.1, 9.2 In a given solution, be able to identify the solvent and the solute Be able to describe what interactions must be broken and formed to dissolve a substance and under what conditions that dissolving process will be endothermic versus exothermic Be able to explain WHY like dissolves like from the point of view of breaking and forming intermolecular attractions Given two substances, be able to predict whether they are likely to be miscible or not and explain WHY Be able to describe how to make a saturated, unsaturated, or supersaturated solution Be able to describe and explain how and why the solubility of a solid dissolved in a liquid changes (generally) upon increasing temperature Be able to describe and explain how and why the solubility of a gas dissolved in a liquid changes upon changing the temperature, volume of gas, or moles of gas Be able to identify a compound as a strong electrolyte, weak electrolyte, or nonelectrolyte and EXPLAIN your identification

Practice Problems for Sections 13.2, 13.1, 13.4, Complete these problems outside of class until you are confident you have learned the SKILLS in this section outlined on the study guide and we will review some of them next class period

Prep for Day 26 Must Watch videos: (energy, crash course chemistry) (exo vs endo, Tyler DeWitt) (calorimetry, crash course chemistry) (calorimetry, Tyler DeWitt) Other helpful videos: (Energy, UC-Berkeley, lessons 19, 20.1, 21.1, and 21.2) YhQrUhttps:// YhQrU (Energy, UC-Irvine) Read Sections