Chapter Menu Acids and Bases Section 18.1Section 18.1Introduction to Acids and Bases Section 18.2Section 18.2 Strengths of Acids and Bases Section 18.3Section 18.3 Hydrogen Ions and pH Section 18.4Section 18.4 Neutralization Exit Click a hyperlink or folder tab to view the corresponding slides.

Section 18-1 Section 18.1 Introduction to Acids and Bases Identify the physical and chemical properties of acids and bases. Lewis structure: a model that uses electron-dot structures to show how electrons are arranged in molecules Classify solutions as acidic, basic, or neutral. Compare the Arrhenius, Brønsted-Lowry, and Lewis models of acids and bases.

Section 18-1 Section 18.1 Introduction to Acids and Bases (cont.) acidic solution basic solution Arrhenius model Brønsted-Lowry model conjugate acid Different models help describe the behavior of acids and bases. conjugate base conjugate acid-base pair amphoteric Lewis model

Section 18-1 Properties of Acids and Bases Acids taste sour. Acids and bases are both conductors of electricity. They are called electrolytes because they generate ions in solution. Acids turn blue litmus red. Bases taste bitter Bases feel slippery. Bases turn red litmus blue.

Section 18-1 Properties of Acids and Bases (cont.) Acids and bases can be identified by their reactions with some metals and metal carbonates. Magnesium and zinc react with acids to produce hydrogen gas. Geologists identify limestone (CaCO 3 ) because it produces bubbles of carbon dioxide when exposed to hydrochloric acid. Mg(s) + 2HCl(aq)  MgCl 2 (aq) + H 2 (g)

Section 18-1 Properties of Acids and Bases (cont.) All water solutions contain hydrogen ions (H + ) and hydroxide ions (OH – ). An acidic solution contains more hydrogen ions than hydroxide ions.acidic solution A basic solution contains more hydroxide ions than hydrogen ions.basic solution

Section 18-1 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. H 2 O(l) + H 2 O(l) ↔ H 3 O + (aq) + OH – (aq) The hydronium ion is H 3 O +. (same as H + )

Section 18-1 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.Arrhenius model ***Arrhenius model states an acid produces hydrogen ions (H + ) and a base produces a hydroxide ion (OH - )***

Section 18-1 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.

Section 18-1 The Brønsted-Lowry Model The Brønsted-Lowry Model of acids and bases states that an acid is a hydrogen ion donor, and a base is a hydrogen ion acceptor.Brønsted-Lowry Model The Brønsted-Lowry Model is a more inclusive model of acids and bases. You need to look at the equation to see what the substance does to decide if it acted as an acid or a base.

Section 18-1 The Brønsted-Lowry Model (cont.) A conjugate acid is the species produced when a base accepts a hydrogen ion.conjugate acid A conjugate base is the species produced when an acid donates a hydrogen ion.conjugate base A conjugate acid-base pair consists of two substances related to each other by donating and accepting a single hydrogen ion.conjugate acid-base pair

Section 18-1 The Brønsted-Lowry Model (cont.) Hydrogen fluoride—a Brønsted-Lowry acid HF(aq) + H 2 O(l) ↔ H 3 O + (aq) + F – (aq) AcidBaseConjugate acid Conjugate Base

Section 18-1 The Brønsted-Lowry Model (cont.) Ammonia— Brønsted-Lowry base NH 3 (aq) + H 2 O(l) ↔ NH 4 + (aq) + OH – (aq) Water and other substances that can act as acids or bases are called amphoteric.amphoteric BaseAcid Conjugate acid Conjugate base

Section 18-1 The Lewis Model According to the Lewis model, a Lewis acid is an electron-pair acceptor and a Lewis base is an electron pair donor.Lewis model The Lewis model includes all the substances classified as Brønsted-Lowry acids and bases and many more.

Section 18-1 Monoprotic and Polyprotic Acids An acid that can donate only one hydrogen ion is a monoprotic acid. Only ionizable hydrogen atoms can be donated.

Section 18-1 Monoprotic and Polyprotic Acids (cont.) Acids that can donate more than one hydrogen ion are polyprotic acids.

Anhydrides – oxides that will combine with water to form acids or bases. metal oxides will form bases nonmetal oxides will form acids CO 2 + H 2 O  H 2 CO 3 P 2 O H 2 O  2 H 3 PO 4 Li 2 O + H 2 O  2 LiOH CaO + H 2 O  Ca(OH) 2

Write the anhydride for each of these acids or bases. H 2 SO 4 HNO 3 NaOH Ba(OH) 2 SO 3 N2O5N2O5 Na 2 O BaO HNO 3 - H 2 O N2O5N2O5

A.A B.B C.C D.D Section 18-1 Section 18.1 Assessment A Lewis acid is a(n) ____. A.electron pair donor B.hydrogen ion donor C.electron pair acceptor D.substance that contains an hydroxide group

A.A B.B C.C D.D Section 18-1 Section 18.1 Assessment A conjugate acid is formed when: A.a base accepts a hydrogen ion B.an acid accepts a hydrogen ion C.an acid donates a hydrogen ion D.a base donates a hydrogen ion

End of Section 18-1

Section 18-2 Section 18.2 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.

Section 18-2 Section 18.2 Strengths of Acids and Bases (cont.) 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.

Section 18-2 Strengths of Acids Acids that ionize completely are strong acids.strong acids Because they produce the maximum number of hydrogen ions, strong acids are good conductors of electricity. The 6 common strong acids are: HCl HBr HIH 2 SO 4 HNO 3 HClO 4

Section 18-2 Strengths of Acids (cont.) Acids that only partially ionize in dilute aqueous solutions are called weak acids.weak acids “learn the strong, the rest are weak”

Strong does not mean concentrated. HCl is a strong acid, so it will always be completely ionized. H+H+ Cl - H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ dilute concentrated

Weak does not mean dilute. HF is a weak acid, so it will only be partially ionized. H+H+ HF H+H+ F-F- H+H+ F-F- F-F- dilute concentrated

Section 18-2 Strengths of Acids (cont.) The equilibrium constant, K eq, provides a quantitative measure of the degree of ionization of an acid. The acid ionization constant is the value of the equilibrium constant expression for the ionization of a weak acid, K a.acid ionization constant HBr  H + + Br - K a = [H + ][Br - ] [HBr]

Section 18-2 Strengths of Acids (cont.) For weak acids, the products tend to be small compared to the un-ionized molecules (reactant). Weaker acids have a smaller K a.

Section 18-2 Strengths of Bases A base that dissociates completely into metal ions and hydroxide ions is known as a strong base. strong base The strong bases are the soluble hydroxides: G1 hydroxides plus Ca(OH) 2 Sr(OH) 2 and Ba(OH) 2

Section 18-2 Strengths of Bases (cont.) The base ionization constant, K b, is the value of the equilibrium constant expression for the ionization of a base.base ionization constant A weak base ionizes only partially in dilute aqueous solution.weak base

Section 18-3 pH and pOH Concentrations of H + ions are often small numbers expressed in exponential notation. pH is the negative logarithm of the hydrogen ion concentration of a solution. pH = –log [H + ]pH

Section 18-3 pH and pOH (cont.) pOH of a solution is the negative logarithm of the hydroxide ion concentration.pOH pOH = –log [OH – ] The sum of pH and pOH equals 14.