CHEMISTRY Matter and Change Chapter 18: Acids and Bases

Section 18.1 Introduction to Acids and Bases CHAPTER18 Table Of Contents Section 18.1 Introduction to Acids and Bases Section 18.2 Strengths of Acids and Bases Section 18.3 Hydrogen Ions and pH Section 18.4 Neutralization Click a hyperlink to view the corresponding slides. Exit

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases Identify the physical and chemical properties of acids and bases. Classify solutions as acidic, basic, or neutral. Compare the Arrhenius, Brønsted-Lowry, and Lewis models of acids and bases. Lewis structure: a model that uses electron-dot structures to show how electrons are arranged in molecules

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases acidic solution basic solution Arrhenius model Brønsted-Lowry model conjugate acid conjugate base conjugate acid-base pair amphoteric Lewis model Different models help describe the behavior of acids and bases.

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases Properties of Acids and Bases Acids taste sour. Bases taste bitter and feel slippery. Acids and bases are conductors of electricity. Acids and bases can be identified by their *

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases Properties of Acids and Bases (cont.) Acids turn blue litmus red. Bases turn red litmus blue. Magnesium and zinc react with acids to produce hydrogen gas. Geologists identify limestone because it produces bubbles of carbon dioxide when exposed to hydrochloric acid.

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases Properties of Acids and Bases (cont.) All water solutions contain hydrogen ions (H+) and hydroxide ions (OH–). An acidic solution contains more * A basic solution contains more *

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases Properties of Acids and Bases (cont.) The usual solvent for acids and bases is water—water produces equal numbers of hydrogen and hydroxide ions in a process called self-ionization. H2O(l) + H2O(l) H3O+(aq) + OH–(aq) The hydronium ion is H3O+.

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases The Arrhenius Model The Arrhenius model states that an acid is a substance that contains hydrogen and ionizes to produce hydrogen ions in aqueous solution, and a base is a substance that contains a hydroxide group and dissociates to produce a hydroxide ion in solution.

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases The Arrhenius Model (cont.) Arrhenius acids and bases HCl ionizes to produce H+ ions. HCl(g) → H+(aq) + Cl–(aq) NaOH dissociates to produce OH– ions. NaOH(s) → Na+(aq) + OH–(aq) Some solutions produce hydroxide ions even though they do not contain a hydroxide group.

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases The Brønsted-Lowry Model The Brønsted-Lowry Model of acids and bases states that * The Brønsted-Lowry Model is a more inclusive model of acids and bases.

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases The Brønsted-Lowry Model (cont.) A conjugate acid is the species produced when * A conjugate base is the species produced when * A conjugate acid-base pair consists of two substances related to each other by *

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases The Brønsted-Lowry Model (cont.) Hydrogen fluoride—a Brønsted-Lowry acid HF(aq) + H2O(l) ↔ H3O+(aq) + F–(aq) HF = acid, H2O = base, H3O+ = conjugate acid, F– = conjugate base

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases The Brønsted-Lowry Model (cont.) Ammonia— Brønsted-Lowry base NH3(aq) + H2O(l) ↔ NH4+(aq) + OH–(aq) NH3 = base, H2O(l) = acid, NH4+ = conjugate acid, OH– = conjugate base * are called amphoteric.

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases Monoprotic and Polyprotic Acids An acid that can donate only one hydrogen ion is a monoprotic acid. Only ionizable hydrogen atoms can be donated.

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases Monoprotic and Polyprotic Acids Acids that can donate more than one hydrogen ion are polyprotic acids.

Introduction to Acids and Bases SECTION18.1 Introduction to Acids and Bases The Lewis Model According to the Lewis model, a Lewis acid is * The Lewis model includes all the substances classified as Brønsted-Lowry acids and bases and many more.

Strengths of Acids and Bases SECTION18.2 Strengths of Acids and Bases Relate the strength of an acid or base to its degree of ionization. electrolyte: an ionic compound whose aqueous solution conducts an electric current Compare the strength of a weak acid with the strength of its conjugate base. Explain the relationship between the strengths of acids and bases and the values of their ionization constants.

Strengths of Acids and Bases SECTION18.2 Strengths of Acids and Bases strong acid weak acid acid ionization constant strong base weak base base ionization constant In solution, strong acids and bases ionize completely, but weak acids and bases ionize only partially.

Strengths of Acids and Bases SECTION18.2 Strengths of Acids and Bases Strengths of Acids * are strong acids. Because they produce the maximum number of hydrogen ions, strong acids are good conductors of electricity.

Strengths of Acids and Bases SECTION18.2 Strengths of Acids and Bases Strengths of Acids (cont.) * are called weak acids.

Strengths of Acids and Bases SECTION18.2 Strengths of Acids and Bases Strengths of Acids (cont.) With a strong acid, the conjugate base is a weak base. Equilibrium lies almost completely to the right in the equation because the conjugate base has a weaker attraction for the H+ ion than does the base in the forward reaction. In a weak acid, the ionization equilibrium lies to the far left in the ionization equation because the conjugate base has a greater attraction for H+ ions than does the base in the forward reaction.

Strengths of Acids and Bases SECTION18.2 Strengths of Acids and Bases Strengths of Acids (cont.) The equilibrium constant, Keq, provides a quantitative measure of the degree of ionization of an acid. The acid ionization constant is * Ka indicates whether products or reactants are favored at equilibrium.

Strengths of Acids and Bases SECTION18.2 Strengths of Acids and Bases Strengths of Acids (cont.) For weak acids, the products tend to be smaller compared to the un-ionized molecules (reactant). Weaker acids have a smaller Ka.

Strengths of Acids and Bases SECTION18.2 Strengths of Acids and Bases Strengths of Bases *is known as a strong base. A weak base *

Strengths of Acids and Bases SECTION18.2 Strengths of Acids and Bases Strengths of Bases (cont.) The base ionization constant, Kb, is the value of the equilibrium constant expression for the ionization of a base.

Hydrogen Ions and pH Explain pH and pOH. SECTION18.3 Hydrogen Ions and pH Explain pH and pOH. Le Châtelier’s principle: states that if a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress Relate pH and pOH to the ion product constant for water. Calculate the pH and pOH of aqueous solutions. pH and pOH are logarithmic scales that express the concentrations of hydrogen ions and hydroxide ions in aqueous solutions. ion product constant for water pH pOH

Ion Product Constant for Water SECTION18.3 Hydrogen Ions and pH Ion Product Constant for Water Pure water contains equal concentrations of H+ and OH– ions. The ion product constant of water, Kw = [H+][OH–]. The ion product constant for water is the value of the equilibrium constant expression for the self-ionization of water.

Ion Product Constant for Water (cont.) SECTION18.3 Hydrogen Ions and pH Ion Product Constant for Water (cont.) With pure water at 298 K, both [H+] and [OH–] are equal to 1.0 × 10–7M. Kw at 298 K = 1.0 × 10–14 Kw and LeChâtelier’s Principle proves [H+] × [OH–] must equal 1.0 × 10–14 at 298 K, and as [H+] goes up, [OH–] must go down.

Hydrogen Ions and pH pH and pOH SECTION18.3 Hydrogen Ions and pH pH and pOH Concentrations of H+ ions are often small numbers expressed in scientific notation. pH is the * pH = –log [H+]

Hydrogen Ions and pH pH and pOH (cont.) pOH of a solution is * SECTION18.3 Hydrogen Ions and pH pH and pOH (cont.) pOH of a solution is * pOH = –log [OH–] The sum of pH and pOH equals 14.

Hydrogen Ions and pH pH and pOH (cont.) SECTION18.3 Hydrogen Ions and pH pH and pOH (cont.) For all strong monoprotic acids, the concentration of the acid is the concentration of H+ ions. For all strong bases, the concentration of the OH– ions available is the concentration of the base. Weak acids and weak bases only partially ionize and Ka and Kb values must be used.

Hydrogen Ions and pH pH and pOH (cont.) SECTION18.3 Hydrogen Ions and pH pH and pOH (cont.) Litmus paper and a pH meter with electrodes can determine the pH of a solution.

Neutralization Write chemical equations for neutralization reactions. SECTION18.4 Neutralization Write chemical equations for neutralization reactions. stoichiometry: the study of quantitative relationships between the amounts of reactants used and products formed by a chemical reaction; is based on the law of conservation of mass Explain how neutralization reactions are used in acid-base titrations. Compare the properties of buffered and unbuffered solutions.

Neutralization neutralization reaction salt titration titrant SECTION18.4 Neutralization neutralization reaction salt titration titrant equivalence point acid-base indicator end point salt hydrolysis buffer buffer capacity In a neutralization reaction, an acid reacts with a base to produce a salt and water.

Reactions Between Acids and Bases SECTION18.4 Neutralization Reactions Between Acids and Bases A neutralization reaction is a reaction in which an * A salt is an * Neutralization is a double-replacement reaction.

Reactions Between Acids and Bases (cont.) SECTION18.4 Neutralization Reactions Between Acids and Bases (cont.)

Reactions Between Acids and Bases (cont.) SECTION18.4 Neutralization Reactions Between Acids and Bases (cont.) Titration is a method for determining the concentration of a solution by *

Reactions Between Acids and Bases (cont.) SECTION18.4 Neutralization Reactions Between Acids and Bases (cont.) In a titration procedure, a measured volume of an acid or base of unknown concentration is placed in a beaker, and initial pH recorded. A buret is filled with the titrating solution of known concentration, called a titrant.

Reactions Between Acids and Bases (cont.) SECTION18.4 Neutralization Reactions Between Acids and Bases (cont.) Measured volumes of the standard solution are added slowly and mixed into the solution in the beaker, and the pH is read and recorded after each addition. The process continues until the reaction reaches the equivalence point, which is the point at which * An abrupt change in pH occurs at the equivalence point.

Reactions Between Acids and Bases (cont.) SECTION18.4 Neutralization Reactions Between Acids and Bases (cont.)

Reactions Between Acids and Bases (cont.) SECTION18.4 Neutralization Reactions Between Acids and Bases (cont.) Chemical dyes whose color are affected by acidic and basic solutions are called acid-base indicators.

Reactions Between Acids and Bases (cont.) SECTION18.4 Neutralization Reactions Between Acids and Bases (cont.) An end point is the point at which an indicator used in a titration changes color. An indicator will change color at the equivalence point.

Neutralization Salt Hydrolysis SECTION18.4 Neutralization Salt Hydrolysis In salt hydrolysis, the anions of the dissociated salt accept hydrogen ions from water or the cations of the dissociated salt donate hydrogen ions to water.

Salt Hydrolysis (cont.) SECTION18.4 Neutralization Salt Hydrolysis (cont.) Salts that produce basic solutions KF is the salt of a strong base (KOH) and a weak acid (HF). KF(s) → K+(aq) + F–(aq)

Salt Hydrolysis (cont.) SECTION18.4 Neutralization Salt Hydrolysis (cont.) Salts that produce acidic solutions NH4Cl is the salt of a weak base (NH3) and strong acid (HCl). When dissolved in water, the salt dissociates into ammonium ions and chloride ions. NH4Cl(s) → NH4+(aq) + Cl–(aq)

Salt Hydrolysis (cont.) SECTION18.4 Neutralization Salt Hydrolysis (cont.) Salts that produce neutral solutions NaNO3 is the salt of a strong acid (HNO3) and a strong base (NaOH). Little or no salt hydrolysis occurs because neither Na+ nor NO3– react with water.

Neutralization Buffered Solutions SECTION18.4 Neutralization Buffered Solutions The pH of blood must be kept in within a narrow range. Buffers are * A buffer is a solution made up of a weak species and its conjugate.

Buffered Solutions (cont.) SECTION18.4 Neutralization Buffered Solutions (cont.) Ions and molecules in a buffer solution resist changes in pH by reacting with any hydrogen ions or hydroxide ions added to the buffered solution. HF(aq) H+(aq) + F–(aq) When acid is added, the equilibrium shifts to the left.

Buffered Solutions (cont.) SECTION18.4 Neutralization Buffered Solutions (cont.) Additional H+ ions react with F– ions to form undissociated HF molecules but the pH changes little. * is called the buffer capacity.

Buffered Solutions (cont.) SECTION18.4 Neutralization Buffered Solutions (cont.) A buffer is most effective when the concentrations of the conjugate acid-base pair are equal or nearly equal.