Brønsted-Lowry definition of an acid: An acid is a proton donor. 721

Brønsted-Lowry definition of an acid: An acid is a proton donor. Brønsted-Lowry definition of a base: A base is a proton acceptor. 722

Brønsted-Lowry definition of an acid: An acid is a proton donor. Brønsted-Lowry definition of a base: A base is a proton acceptor. H + (aq) + OH - (aq) H 2 O (l) acid base 723

Brønsted-Lowry definition of an acid: An acid is a proton donor. Brønsted-Lowry definition of a base: A base is a proton acceptor. H + (aq) + OH - (aq) H 2 O (l) acid base HCl (g) + NH 3(g) NH 4 Cl (s) acid base 724

Brønsted-Lowry definition of an acid: An acid is a proton donor. Brønsted-Lowry definition of a base: A base is a proton acceptor. H + (aq) + OH - (aq) H 2 O (l) acid base HCl (g) + NH 3(g) NH 4 Cl (s) acid base Note in this latter example, there is no water present. 725

Strong and Weak Acids: 726

Strong and Weak Acids: HBr (g) + H 2 O (l) H 3 O + (aq) + Br - (aq) 727

Strong and Weak Acids: HBr (g) + H 2 O (l) H 3 O + (aq) + Br - (aq) 728

Strong and Weak Acids: HBr (g) + H 2 O (l) H 3 O + (aq) + Br - (aq) K c is large – the concentration of HBr at equilibrium is very small. 729

Strong and Weak Acids: HBr (g) + H 2 O (l) H 3 O + (aq) + Br - (aq) K c is large – the concentration of HBr at equilibrium is very small. The size of K c can be used to indicate the strength of an acid, but there is a more convenient way to represent data on acid strengths, which will be treated shortly. 730

HF (g) + H 2 O (l) H 3 O + (aq) + F - (aq) 731

HF (g) + H 2 O (l) H 3 O + (aq) + F - (aq) 732

HF (g) + H 2 O (l) H 3 O + (aq) + F - (aq) K c for this acid is small. This means the concentration of H 3 O + at equilibrium is small. 733

HF (g) + H 2 O (l) H 3 O + (aq) + F - (aq) K c for this acid is small. This means the concentration of H 3 O + at equilibrium is small. HF (aq) is a weak acid. 734

HF (g) + H 2 O (l) H 3 O + (aq) + F - (aq) K c for this acid is small. This means the concentration of H 3 O + at equilibrium is small. HF (aq) is a weak acid. Note that a weak acid can be corrosive. HF (aq) is a very corrosive acid – it attacks glass. 735

Strong and weak bases. NH H 2 O (l) NH 3(aq) + OH - (aq) 736

Strong and weak bases. NH H 2 O (l) NH 3(aq) + OH - (aq) amide ion 737

Strong and weak bases. NH H 2 O (l) NH 3(aq) + OH - (aq) amide ion K c for this reaction is large, indicating the amide ion is a strong base. 738

Strong and weak bases. NH H 2 O (l) NH 3(aq) + OH - (aq) amide ion K c for this reaction is large, indicating the amide ion is a strong base. NH 3(g) + H 2 O (l) NH 4 + (aq) + OH - (aq) 739

Strong and weak bases. NH H 2 O (l) NH 3(aq) + OH - (aq) amide ion K c for this reaction is large, indicating the amide ion is a strong base. NH 3(g) + H 2 O (l) NH 4 + (aq) + OH - (aq) K c for this reaction is small, indicating that NH 3 is a weak base. 740

Amphoteric compounds: Compounds that can function as either acids or bases, depending on the other substances present. 741

Amphoteric compounds: Compounds that can function as either acids or bases, depending on the other substances present. Example: HCO

Amphoteric compounds: Compounds that can function as either acids or bases, depending on the other substances present. Example: HCO 3 - HCO 3 - (aq) + H 3 O + (aq) H 2 CO 3(aq) + H 2 O 743

Amphoteric compounds: Compounds that can function as either acids or bases, depending on the other substances present. Example: HCO 3 - HCO 3 - (aq) + H 3 O + (aq) H 2 CO 3(aq) + H 2 O base in this reaction 744

Amphoteric compounds: Compounds that can function as either acids or bases, depending on the other substances present. Example: HCO 3 - HCO 3 - (aq) + H 3 O + (aq) H 2 CO 3(aq) + H 2 O base in this reaction HCO 3 - (aq) + OH - (aq) CO 3 2- (aq) + H 2 O 745

Amphoteric compounds: Compounds that can function as either acids or bases, depending on the other substances present. Example: HCO 3 - HCO 3 - (aq) + H 3 O + (aq) H 2 CO 3(aq) + H 2 O base in this reaction HCO 3 - (aq) + OH - (aq) CO 3 2- (aq) + H 2 O acid in this reaction 746

Amphiprotic: A substance that can function as an acid or a base. 747

Conjugate acid-base relationships 748

Conjugate acid-base relationships Consider the equilibrium: HCN (aq) + H 2 O H 3 O + (aq) + CN - (aq) 749

Conjugate acid-base relationships Consider the equilibrium: HCN (aq) + H 2 O H 3 O + (aq) + CN - (aq) conjugate acid-base pair 750

Conjugate acid-base relationships Consider the equilibrium: conjugate acid-base pair HCN (aq) + H 2 O H 3 O + (aq) + CN - (aq) conjugate acid-base pair 751

Conjugate acid-base relationships Consider the equilibrium: conjugate acid-base pair HCN (aq) + H 2 O H 3 O + (aq) + CN - (aq) conjugate acid-base pair The formulas of any conjugate acid-base pair differ only by one H +. CN - is a base, because of the reaction: 752

H 3 O + (aq) + CN - (aq) HCN (aq) + H 2 O 753

H 3 O + (aq) + CN - (aq) HCN (aq) + H 2 O stronger stronger weaker weaker acid base acid base 754

H 3 O + (aq) + CN - (aq) HCN (aq) + H 2 O stronger stronger weaker weaker acid base acid base The conjugate acid-base relationship can be written in generic format as: 755

H 3 O + (aq) + CN - (aq) HCN (aq) + H 2 O stronger stronger weaker weaker acid base acid base The conjugate acid-base relationship can be written in generic format as: acid 1 + base 2 acid 2 + base 1 756

H 3 O + (aq) + CN - (aq) HCN (aq) + H 2 O stronger stronger weaker weaker acid base acid base The conjugate acid-base relationship can be written in generic format as: acid 1 + base 2 acid 2 + base 1 757

H 3 O + (aq) + CN - (aq) HCN (aq) + H 2 O stronger stronger weaker weaker acid base acid base The conjugate acid-base relationship can be written in generic format as: acid 1 + base 2 acid 2 + base 1 758

759

Self-Dissociation of Water 760

Self-Dissociation of Water Water dissociates to give very low concentrations of hydronium and hydroxide ions: 761

Self-Dissociation of Water Water dissociates to give very low concentrations of hydronium and hydroxide ions: H 2 O + H 2 O H 3 O + (aq) + OH - (aq) 762

Self-Dissociation of Water Water dissociates to give very low concentrations of hydronium and hydroxide ions: H 2 O + H 2 O H 3 O + (aq) + OH - (aq) The position of this equilibrium lies strongly on the left (at 25 o C): 763

Self-Dissociation of Water Water dissociates to give very low concentrations of hydronium and hydroxide ions: H 2 O + H 2 O H 3 O + (aq) + OH - (aq) The position of this equilibrium lies strongly on the left (at 25 o C): 764

At equilibrium and at 25 o C, the concentrations are [H 3 O + ] = [OH - ] = 1.00 x M, and [H 2 O] = 55.5 M. 765

At equilibrium and at 25 o C, the concentrations are [H 3 O + ] = [OH - ] = 1.00 x M, and [H 2 O] = 55.5 M. Because the concentration of H 3 O + is so small, the concentration of H 2 O is essentially constant. That is, it is almost a pure liquid. The preceding expression for K c can be simplified. We can write: 766

At equilibrium and at 25 o C, the concentrations are [H 3 O + ] = [OH - ] = 1.00 x M, and [H 2 O] = 55.5 M. Because the concentration of H 3 O + is so small, the concentration of H 2 O is essentially constant. That is, it is almost a pure liquid. The preceding expression for K c can be simplified. We can write: 767

At equilibrium and at 25 o C, the concentrations are [H 3 O + ] = [OH - ] = 1.00 x M, and [H 2 O] = 55.5 M. Because the concentration of H 3 O + is so small, the concentration of H 2 O is essentially constant. That is, it is almost a pure liquid. The preceding expression for K c can be simplified. We can write: Now set K w =, so that at 25 o C 768

At equilibrium and at 25 o C, the concentrations are [H 3 O + ] = [OH - ] = 1.00 x M, and [H 2 O] = 55.5 M. Because the concentration of H 3 O + is so small, the concentration of H 2 O is essentially constant. That is, it is almost a pure liquid. The preceding expression for K c can be simplified. We can write: Now set K w =, so that at 25 o C 769

At equilibrium and at 25 o C, the concentrations are [H 3 O + ] = [OH - ] = 1.00 x M, and [H 2 O] = 55.5 M. Because the concentration of H 3 O + is so small, the concentration of H 2 O is essentially constant. That is, it is almost a pure liquid. The preceding expression for K c can be simplified. We can write: Now set K w =, so that at 25 o C The w subscript refers to water. 770

Criteria for Acidic, Basic, and neutral solutions 771

Criteria for Acidic, Basic, and neutral solutions Neutral solution: [H 3 O + ] = [OH - ] 772

Criteria for Acidic, Basic, and neutral solutions Neutral solution: [H 3 O + ] = [OH - ] Acidic solution: [H 3 O + ] > [OH - ] 773

Criteria for Acidic, Basic, and neutral solutions Neutral solution: [H 3 O + ] = [OH - ] Acidic solution: [H 3 O + ] > [OH - ] Basic solution: [H 3 O + ] < [OH - ] 774

The pH concept 775

The pH concept To avoid awkward numbers such as 9.2 x when dealing with H 3 O + concentrations, the following concept is employed: 776

The pH concept To avoid awkward numbers such as 9.2 x when dealing with H 3 O + concentrations, the following concept is employed: pH = - log[H + ] 777

The pH concept To avoid awkward numbers such as 9.2 x when dealing with H 3 O + concentrations, the following concept is employed: pH = - log[H + ] This is actually shorthand for pH = - log([H + ]/M) 778

The exact definition of pH is The exact definition of pH is: 779

The exact definition of pH is The exact definition of pH is: is called the activity of the hydrogen ion. 780