Chemistry Outcomes Review: Chapter 2

Aqueous Solutions and Solubility

In this chapter, we developed a few simple rules that permit you to predict solubilities or relative solubilities of molecules and ionic solids in water. To explain these rules, we discussed the factors (energy and molecular reorganization) that control the solubility of solutes in water and found that there is a maximum solubility (saturation) for most solutes when the pure solute and dissolved solute are in equilibrium.

We examined two properties of solutions, electrical conductivity and pH, that provide evidence for molecular level representations of aqueous solutions as solutions of hydrated molecules and/or ions. We found that water is a reactant in many solutions, especially in acid-base systems, and that acid-base reactions can affect solubilities. We defined solution concentrations in terms of molarity, mole/liter, and applied mole concepts to solutions by analyzing the stoichiometry of precipitation and acid-base reactions.

Check your understanding of the ideas in the chapter by reviewing these expected outcomes of your study.

You should be able to:

  • Use an energy diagram to characterize the basic steps in the dissolving process and give a molecular level explanation for the direction of the individual and net energy changes [Section 2.1].
  • Use molecular models, Lewis structures, and other representations of molecules to show how the three major attractions between like and unlike molecules, hydrogen bonding, dipole-dipole attractions, and London dispersion forces, affect the solubility of a given molecular solute in water [Section 2.2].
  • Give a molecular level explanation for the favorable and unfavorable factors that determine the solubility of a given molecular solute [Section 2.2].
  • Predict the relative aqueous solubilities of a given set of molecular solutes [Section 2.2].
  • Show the direction of motion of the molecules and ions in a solution being tested with an electrical conductivity tester [Section 2.3].
  • Write the chemical formula of any ionic compound, given the charges on the cation and anion [Section 2.4].
  • Draw an energy diagram for the formation of an ionic crystalline compound from its elemental gas phase atoms and give a molecular level explanation for the direction of the energy changes of the individual steps [Section 2.4].
  • Make a drawing showing the process of dissolving a polar solute or an ionic compound that shows how water molecules hydrate the dissolved molecules or ions [Sections 2.3, 2.5].
  • Draw an energy diagram for the dissolution of an ionic crystalline compound in water and give a molecular level explanation for the direction of the energy changes of the individual steps [Section 2.5].
  • Use lattice and hydration energies to determine whether a given ionic compound will dissolve exothermically or endothermically in water [Section 2.5].
  • Give a molecular level explanation for the favorable and unfavorable factors that determine the solubility of a given ionic compound [Section 2.7].
  • Predict whether a precipitate will form when two ionic solutions are mixed [Sections 2.6, 2.7].
  • Carry out these interconversions: grams to moles of a compound, volume of a solution of known concentration to moles (grams) of solute in that volume, and moles (grams) of reactant to moles (grams) of product in a stoichiometric reaction [Sections 2.8, 2.9, 2.10, and 2.14].
  • Prepare (give step-by-step instructions for preparing) an aqueous solution of a specified molarity in some solute [Section 2.9].
  • Determine the limiting reactant in a reaction mixture (solution) and the concentrations of all species formed or remaining in the solution when the reaction is complete [Section 2.10].
  • Use conductivity and/or pH data to determine whether a solute undergoes an acid-base reaction with water and, if so, write the equation for the chemical reaction [Section 2.11].
  • Use the concentration of hydronium ion, hydroxide ion, or the pH to tell whether an aqueous solution is acidic or basic [Sections 2.12 and 2.14].
  • Write the equation for the reaction between Bronsted-Lowry acids and bases and identify the Bronsted-Lowry conjugate acid-base pairs in any acid-base reaction [Sections 2.12, 2.13].
  • Draw a molecular-level diagram and/or explain in words the reactions occurring in a reacting system (dissolution, precipitation, or acid-base) at equilibrium [Sections 2.6, 2.12, 2.13, and 2.15].
  • Identify examples in which acid-base and precipitation-solubility reactions affect one another and show how observed effects are explained by these interactions [Section 2.15].