Aqueous Reactions and Solution Stoichiometry Honors Chemistry Mr. Kinton Enloe High School

Colligative Properties Properties of a solvent that depend on the total concentration of the solute particles present Vapor pressure, boiling-point elevation, freezing-point depression, and osmotic pressure

Vapor Pressure Pressure exerted by a vapor on a liquid in a closed container at equilibrium Nonvolatile: a substance with no measurable vapor pressure Volatile: substance with a measurable vapor pressure Vapor pressure will be lowered with the addition of a nonvolatile solute to a solvent

Boiling-Point Elevation When additional solute is added, the boiling point of a solution will increase Depending on the type of solute will determine how much the boiling point will increase Strong electrolytes increase boiling point more than a nonelectrolyte

Freezing-Point Depression When a solute is added to a solution that will cause the freezing point to decrease Just like with boiling-point elevation, the type of solute in the solvent influences how much freezing point changes

Osmotic Pressure The net movement of solvent molecules from the less concentrated solution to the more concentrated solution Osmotic pressure is the pressure exerted in a solution to prevent the movement of solvent

Net Ionic Equations Double replacement reactions occur in aqueous solution Molecular Equation: equation that shows the complete chemical formulas of the reactants and products without indicating ionic character Complete Ionic Equation: equation that shows all soluble strong electrolytes as ions Spectator Ions: Ions that appear in identical forms on the reactants and products side. These ions play no direct role in the reation

Net Ionic Equations Net Ionic Equations: Equation that omits the spectator ions leaving only the ions and molecules directly involved in the reaction If every ion in a complete ionic equation is a spectator, then no reaction occurs

Net Ionic Equations Procedure for writing net ionic equations: Write a balanced molecular equations for the reaction Rewrite the equation to show the ions that form in solution when each soluble strong electrolyte dissociates or ionizes into it ions Only strong electrolytes dissolved in aqueous solution are written in ionic form Identify and cancel spectator ions

Net Ionic Equation Pb(NO3)2(aq)+2KI(aq)PbI2(s)+2KNO3(aq) CaCl2(aq)+Na2CO3(aq)CaCO3(s)+2NaCl(aq) Ba(OH)2(aq)+HC2H3O2(aq)Ba(C2H3O2)2(aq)+H2O(l)

Autoionization of Water Process where one molecule of water donates a proton to another water molecule H2O(l) + H2O(l) H3O+(aq) + OH-(aq) H3O+: Hydronium ion This process happens rapidly and the molecules of water do not stay ionized for long This process occurs at equilibrium, which means the forward and reverse process occur at the same rate

Equilibrium Expression and the Ion Product Constant For any reaction at equilibrium, an equilibrium expression can be written to show which side of the reaction is favored For water, it has an ion product constant (Kw) that equals 1.0 × 10-14 at 25oC This means that the reactants in the autoionization of water are extremely favored Kw = [H3O+][OH-]

Equilibrium Expression and the Ion Product Constant The Kw for water can be used to describe any dilute aqueous solution This will allow us to calculate the [H+] or the [OH-] depending on what we know When [H+]=[OH-], the solution is neutral When [H+]>[OH-], the solution is acidic When [H+]<[OH-], the solution is basic

Solving Equilibrium Expressions Determine if the following solution is acidic, basic, or neutral and solve for the concentration of the missing ion: [H+] = 4 × 10-9 M [OH-] = 1 × 10-7 M [OH-] = 0.010 M

Characteristics of Acids and Bases Ionize in water to produce H+ (Arrhenius) Begin with H Sour taste Cause skin burns Turn litmus paper red and colorless in phenolphthalein Ionize in water to produce OH- (Arrhenius) Ends with OH Bitter taste Feel slippery or soapy Turn litmus paper blue and pink in phenolphthalein

pH Scale Since the concentration of H+ is usually very small we express that concentration using the pH scale pH = -log[H+] or –log[H3O+] pH = 7 is a neutral solution pH < 7 is an acidic solution pH > 7 is a basic solution A change in [H+] by a factor of 10 causes a change in pH of 1 [H+] = 10^-pH

pH Scale In a sample of lemon juice [H+] = 3.8 x 10-4 M. What is the pH? A sample of freshly pressed apple juice has a pH of 3.76. Calculate the [H+].

Other “p” Scales The concentration of hydroxide ion can be measured using pOH pOH = -log[OH-] and [OH-] = 10^-pOH pH + pOH = 14

Solution Stoichiometry Specific application of stoichiometry where concentration can be used as a conversion factor Solution stoichiometry is no different than regular stoichiometry Just remember our conversion factors

Solution Stoichiometry How many grams of Ca(OH)2 are needed to neutralize 25.0 mL of 0.100 M HNO3? How many liters of 0.500 M HCl are needed to react completely with 0.100 mol of Pb(NO3)2, forming a precipitate PbCl2?

Titrations Technique used to determine the concentration of a solute in solution This is done by using a solution with a known concentration (standard solution) Titrations can be used for acid-base reactions, precipitation reactions, and oxidation-reduction reactions

Titrations Equivalence point: the point at which stoichiometrically equivalent quantities are brought together Indicators: used to help chemists identify when the equivalence point has been reached When the indicator changes that signals the end point of the titration which is usually close to the equivalence point

Titrations How many grams of chloride ion are in a sample of the water if 20.2 mL of 0.100 M Ag+ is needed to react with all of the chloride in the sample? 45.7 mL of 0.500 M H2SO4 is required to neutralize a 20.0 mL sample of NaOH solution. What is the concentration of NaOH?