Chapter 20 Acids and Bases Describing Acids and Bases Hydrogen Ions and Acidity Acid-Base Theories Strengths of Acids and Bases

List as many properties of acids and bases as you can remember:

Properties of Acids

Properties of Bases

Determine if the following are acids or bases:

Lime

Vitamin C

DO NOT MIX

Ch 20.1 Describing Acids and Bases

Properties of Acids and Bases Names and Formulas of Acids and Bases

Properties of Acids Corrosive ('burns' your skin) Sour taste (e.g. lemons, vinegar) Contains hydrogen ions (H+) when

dissolved in water Has a pH less than 7 Turns blue litmus paper to a red color Reacts with bases to form salt and water Reacts with metals to form hydrogen gas Reacts with carbonates to form carbon

dioxide, water and a salt

Hydrofluoric Acid Burns

Properties of Bases Corrosive ('burns' your skin) Soapy feel Has a pH more than 7 Turns red litmus paper to a blue color Many alkalis (soluble bases) contain

hydroxyl ions (OH-) Reacts with acids to form salt and water

Sodium Hydroxide Burn

Names and Formulas of Acids

Anion Ending

Example Acid Name Example

-ide Cl- Hydro-(stem)-ic acid Hydrochloric Acid

-ite SO32- (stem) – ous acid Sulfurous Acid

-ate NO3- (stem) –ic acid Nitric Acid

Names and Formulas of Bases No Change Name the cation then the anion NaOH Sodium Hydroxide

Ch 20.2 Hydrogen Ions and Acidity Hydrogen Ions From Water The pH Concept Calculating pH Values Measuring pH

Hydrogen Ions From Water During the collisions of water molecules,

occasionally a hydrogen ion from one molecule is transferred to another

H2O + H2O H3O+ + HO-

This forms a hyrdronium ion and a hydroxide ion. Self Ionization

Hydrogen Ions Names:

Protons Hydrogen Ions Hydronium Ions Solvated Protons

H+ or H3O+

Neutral Solution The [ H+ ] equals [ OH- ]

Ion Product Constant for Water (Kw)

Kw = [ H+ ] [ OH- ] = 1.0x10-14 M2

Types of Solution Acidic Solution - [ H+ ] greater [ OH- ] Basic Solution - [ H+ ] less [ OH- ]

Alkaline Solutions

The pH Concept pH is a simpler way of writing [ H+ ]

pH = -log [ H+ ]

pH + pOH = 14

Arrhenius Acids and Bases 1887 Svante Arrhenius Acids – hydrogen containing compounds

that ionize to yield hydrogen ions in aqueous solutions

Bases - hydroxide containing compounds that ionize to yield hydroxide ions in aqueous solutions

Arrhenius Acids and Bases Monoprotic Acids – contain one ionizable

hydrogen HNO3

Diprotic Acids - contain two ionizable hydrogens H2SO4

Triprotic Acids - contain three ionizable hydrogens H3PO4

Arrhenius Acids and Bases Not all hydrogen's form ions Only those in very polar bonds

HCl CH4

Bronsted-Lowry Acids and Bases

1923 Johannes Bronsted and Thomas Lowry (independent of each other)

Acid – Hydrogen ion donor (proton donor) Base – Hydrogen ion acceptor (proton

acceptor)

Conjugate’s Conjugate Acid - Particle formed when a

base gains a hydrogen ion Conjugate Base - Particle formed when an

acid has donated a hydrogen ion HCl + H2O = H3O+ + Cl-

Acid Base Conjugate Acid Conjugate Base

Lewis Acids and Bases Gilbert Lewis (1875-1946) Lewis Acid – Substance that can accept a

pair of electrons to form a covalent bond Lewis Base - Substance that can donate a

pair of electrons to form a covalent bond

Strengths of Acids and Bases Strong and Weak Acids and Bases Calculating Dissociation Constants

Strong and Weak Acids and Bases

Strong Acid – completely ionized in aqueous solutions

Weak Acid – ionize only slightly in aqueous solutions

Acid Dissociation Constant Ka

The ratio of the concentration of the dissociated form of an acid to the concentration of the undissociated form

CH3COOH(aq) + H2O(l) = H3O+ (aq) + CH3COO-

(aq)

Ka = [H+] [CH3COO-]

[CH3COOH]

Acid Dissociation Constant Ka

Small Ka = weak acid 1.8 x 10-5

Large Ka = strong acid 4.4 x 10-4

Acid Dissociation Constant Ka

Diprotic and Triprotic acids lose their hydrogens one at a time, resulting in more than one Ka

H3PO4 7.5 x 10 –3

6.2 x 10 –8

4.8 x 10 –13

Bases Strong Base – dissociate completely into

metal ions and hydroxide ions in aqueous solutions

Weak Base – form the hydroxide ion and the conjugate acid of the base NH3(aq) + H2O(l) = NH4

+(aq) + OH-

(aq)

Kb = [NH4+] [OH-]

[NH3]

Base Dissociation Constant Kb

Kb = [conjugate acid] [OH-]

[conjugate base]

Small Kb = weak base

Large Kb = strong base